Microwave coagulation applicator and system

Abstract

To provide a microwave ablation treatment that ensures that damage to surrounding normal tissue during treatment is minimized. A microwave applicator for insertion into biological tissue includes a microwave transmission line extending between an attachment end of the applicator and an antenna toward the insertion end of the applicator, with an outer conductive sleeve forming an enclosed fluid space around the transmission line. Circulation of a cooling fluid is guided within the fluid space by a guide sleeve. A sensor senses the approximate temperature of the cooling fluid. A portion of the fluid can be injected into tissue surrounding the applicator to moisten tissue that is not being treated.

Description

[Technical Field]

[0001] The present invention relates to electromagnetic radiation (EMR) therapy, and more particularly to an applicator and system for applying electromagnetic energy to a treatment site in a living body to heat tissue requiring treatment at the treatment site. The present invention is useful for treatments having a microwave coagulation or ablation nature. [Background technology]

[0002] The use of electromagnetic (EM) energy to heat tissue for the treatment of disease is known. When using microwave energy to heat tissue, an applicator having a microwave-emitting antenna is positioned relative to the tissue to be treated (heated) so that the microwave energy emitted from the antenna penetrates and heats the tissue. Many microwave applicators are known in the art. Death, or necrosis, of biological tissue cells occurs at elevated temperatures above normal cell temperatures for a sufficient period of time. The sufficient period generally depends on the temperature to which the cells are heated. Above a threshold temperature of approximately 41.5°C, substantial thermal damage occurs in most malignant cells. At temperatures above approximately 45°C, thermal damage occurs in most cells. During treatment, it is desirable to generate elevated temperatures within the target tissue for a sufficient period of time to produce the desired cell damage, while maintaining a safe, low temperature in surrounding healthy tissue. For this reason, when treatments involving tissue heating are used, it is important to ensure both sufficient tumor heating throughout the tumor up to the tumor border and lower temperatures in critical normal tissue.

[0003] Heat therapy is sometimes combined with other treatments, such as surgery, ionizing radiation, or chemotherapy. For example, when heating is combined with radiation, it is desirable to maintain the temperature within the diseased tissue within a range of approximately 42°C to 45°C. When multimodality therapy is used, high temperatures are usually undesirable because they can lead to the collapse of small blood vessels, creating resistance to radiation therapy and reducing the amount of systemic chemotherapy that reaches the tumor if there is damage to the small blood vessels. Low temperatures are undesirable because they may not provide sufficient therapeutic effect. Therefore, for multimodality therapy, it is important to control the temperature within the desired range and not allow tissue within or around the tumor to heat above 45°C, as this could worsen such tissue damage from other treatments. Treatment within this controlled temperature range is usually referred to as hyperthermia.

[0004] Forms of thermal therapy that kill tissue by heating alone are commonly referred to as coagulation or ablation. To successfully eradicate a cancerous tumor through the application of heat alone, it is necessary to ensure sufficient heating is achieved throughout the tumor. In the case of malignant tumors, if residual tumor cells are left behind, the tumor will rapidly grow back, leaving the patient with the original problem. In what is commonly referred to as microwave coagulation or microwave ablation, diseased tissue is heated to at least above about 55°C, and generally above about 60°C, for an exposure time sufficient to kill the cells, typically greater than about one minute. Microwave coagulation and ablation treatments result in a volume reduction in areas with temperatures ranging from elevated temperatures in the treated tissue to the normal tissue temperature of 37°C outside the treated tissue. The outer edges of the overall heat distribution within the treated tissue volume can, in turn, cause damage to normal tissue if such tissue is overheated. Therefore, prolonged coagulation or ablation treatments, in which the coagulation or ablation volume is maintained at very high temperatures, carry a high risk of damage to surrounding normal tissue. For proper treatment of a targeted cancerous tumor volume, or other tissue volume being treated, it is crucial to properly deliver a precise heat distribution for a sufficient time to eradicate the tumor tissue while minimizing damage to critical surrounding normal tissue. Fortunately, there are tumor locations within normal tissue, such as liver tissue, that can be destroyed by heating in a limited area without affecting the patient's health. In such situations, coagulation can be applied in an aggressive manner to include a safety margin for destruction of the limited surrounding normal tissue to ensure that all of the cancerous tumor is destroyed.

[0005] Rapid heating to high temperatures, common in coagulation and ablation treatments, can use fairly short exposure times. The resulting temperature distribution is primarily a result of the power absorption distribution within the tissue. However, if such treatments continue for many minutes, blood flow and heat conduction in the tumor and surrounding tissue alter the temperature distribution, resulting in a less predictable heat distribution because changes in blood flow in the heated area may not be predictable. It is important to optimize the uniformity of the absorbed tissue heating power, leading to a more predictable temperature distribution that better corresponds to the treatment prescription. Pretreatment planning, both before and possibly during treatment, to calculate the power and temperature distribution resulting from the power parameters and the relative phase of the power applied to the tissue can be important not only for coagulation and ablation but also for hyperthermia treatments. When high temperatures are used during treatment, this can increase patient discomfort and pain, and therefore, it can be useful to avoid excessive temperatures to reduce the need for patient sedation.

[0006] Invasive microwave energy applicators can be inserted into biological tissue to position a heating source within or proximal to a diseased tissue region. Invasive applicators are useful when the target tissue area is located beneath the skin (e.g., the prostate) because they overcome some of the difficulties encountered with surface applicators. Invasive applicators must be properly positioned to localize heating near the desired treatment area. However, even when properly positioned, it has been difficult to ensure sufficient heat is generated in the diseased tissue without overheating the surrounding healthy tissue. Furthermore, in applicators operating at higher power levels to generate the high temperatures necessary for coagulation and ablation, the coaxial cable tends to become undesirably hot in the portion of the applicator where it runs from outside the body to the location of the applicator's radiating antenna, which can cause thermal damage to the normal tissue through which the applicator passes to reach the diseased tissue to be treated. Therefore, various methods of cooling applicators have been used in the prior art.

[0007] In prior art radio frequency (RF) applications, a primary electrode is invasively inserted into the body, while a secondary electrode, for example, in a bipolar RF applicator or separately at another location, is either invasively inserted into the body or placed on the skin outside the body, and a radio frequency heating current is transmitted from the primary electrode to the secondary electrode. In this process, the tissue surrounding the primary electrode tends to dry out and char. When the tissue around the primary electrode, through which the RF heating current must flow to the secondary electrode, dries, the dry tissue around the electrode creates high electrical resistance and inhibits the flow of the heating current. This tissue desiccation, in turn, restricts the current from the primary electrode from flowing beyond the dried or charred tissue, thereby limiting the tissue coagulation zone to that achieved prior to the formation of dried or charred tissue around the electrode. Techniques have been developed to inject a fluid, such as saline, through the tip of such a primary RF electrode, allowing it to heat and replace tissue fluid in this region, thereby maintaining the wettability and conductivity of the tissue near the electrode and reducing the resistance to current flow. This allows the desired current to continue to flow from the primary electrode, producing the desired tissue heating and coagulation. Examples of this are shown in U.S. Patent Nos. 6,066,134, 6,112,123, and 6,131,577. It is also known in the art that fluids, such as saline solutions, can be used with microwave antennas where injection of a fluid, such as saline, is introduced into the primary heating zone to help maintain the antenna's radiation impedance by displacing tissue fluid within the primary radiation and heating region. Examples of this are shown in published U.S. Patent Applications Nos. 2006 / 0122593 and 2009 / 0248006. Other methods for improving impedance matching during microwave coagulation of tissue can also be used, such as fine tuning by frequency variation (U.S. Patent No. 7,594,913) and altering the exposed radiating antenna tip (U.S. Patent Application Publication No. 2009 / 0131926).

[0008] It is also known that in microwave energy applicators, particularly certain applicators operating at 915 MHz, the emitted energy forms a teardrop-shaped heating pattern with tails extending along the applicator shaft from the desired tissue heating zone back toward the proximal end of the applicator into normal tissue along the applicator insertion path. In some cases, the extent of the treating tail varies with the positioning of the applicator, for example, with the applicator's insertion path. This formation of heated tails and the variation in the coagulation zone as a function of varying insertion depth is an undesirable result because, at various reasonable insertion depths, the coagulation zone should be constant and the heating zone produced by the applicator should desirably have a more spherical shape to produce a more spherical ablation zone.

[0009] It has also been found that the frequency of microwaves applied to tissue is a factor in the shape of the heating and ablation zones produced. Microwave frequencies of 915 MHz and 2450 MHz have been approved for medical hyperthermia and ablation applications. The 915 MHz microwaves are longer than the 2450 MHz microwaves. Generally, the longer 913 MHz microwaves penetrate deeper into tissue and have less attenuation as they penetrate into tissue, so they have been found to produce larger heating patterns at a given power level than the higher 2450 MHz microwaves. However, while the longer 913 MHz microwaves produce larger heating patterns, the heating patterns produced by currently available 913 MHz microwave applicators tend to be elliptical in shape, elongating along the applicator from the antenna back outward. The radial diameter of the heating or ablation zone of a single 915 MHz microwave antenna can be as small as half the length of the heating or ablation zone along the applicator. Currently available 2450 MHz frequency microwave applicators also produce slightly elliptical heating patterns, but the heating patterns produced by 2450 MHz frequency microwave applicators tend to be less elliptical and more spherical than those produced by 915 MHz frequency applicators. Thus, 915 MHz provides deeper penetration and longer coagulation pattern lengths, while 2450 MHz provides shallower penetration and shorter coagulation pattern lengths.See, for example, Sun et al., "Comparison of Ablation Zone Between 915- and 2,450-MHz Cooled-Shaft Microwave Antenna: Results in In Vivo Porcine Livers," DOI: 10.2214 / AJR.07.3828 and AJR 2009;192:511-514, and Liu et al., "Comparison of percutaneous 915 MHz microwave ablation and 2450 MHz microwave ablation in large hepatocellular carcinoma," Int. J. Hyperthermia, 2010, 1-8, Early Online. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 6,066,134 [Patent Document 2] U.S. Patent No. 6,112,123 [Patent Document 3] U.S. Patent No. 6,131,577 [Patent Document 4] U.S. Patent Application Publication No. 2006 / 0122593 [Patent Document 5] U.S. Patent Application Publication No. 2009 / 0248006 [Patent Document 6] U.S. Patent No. 7,594,913 [Patent Document 7] U.S. Patent Application Publication No. 2009 / 0131926 [Non-patent literature]

[0011] [Non-Patent Document 1] Sun et al., "Comparison of Ablation Zone Between 915- and 2,450-MHz Cooled-Shaft Microwave Antenna: Results in In Vivo Porcine Livers," DOI:10.2214 / AJR.07.3828 and AJR 2009;192:511-514 [Non-patent document 2] Liu et al., Comparison of percutaneous 915MHz microwave ablation and 2450MHz microwave ablation in large hepatocellular carcinoma

[0012] In tests and simulations conducted by the applicant, the applicant found that using 2450 MHz in single-antenna applicator applications provides shorter ablation and heating lengths along the shaft than using a single-antenna applicator at 915 MHz. This results in a more spherical ablation zone at 2450 MHz than at 915 MHz in single-applicator ablation. Because the cancerous tumors being treated are often substantially spherical in shape, the use of 2450 MHz appears advantageous when a smaller, more spherical ablation pattern is desired, particularly when using a single applicator. However, when multiple applicators are used in a phased array configuration, the 915 MHz frequency can produce a larger, more spherical ablation and heating pattern than an array of multiple antennas operating at 2450 MHz, or single-applicator ablation at either 915 MHz or 2450 MHz. This suggests that the use of 2450 MHz may be advantageous in some situations and 915 MHz in other situations, depending on the size and shape of the mass of diseased tissue being treated. 2450 MHz and 915 MHz microwave tissue treatment systems are currently commercially available as separate systems.

[0013] While many microwave applicators and systems are known in the art for applying microwave energy to tissue to provide heating to the tissue, there is a need for better applicators that are easy to use, have more consistent and predictable heating and ablation patterns, have effective cooling of the applicator shaft, and can provide pathway coagulation or ablation if necessary. Summary of the Invention [Means for solving the problem]

[0014] In accordance with the present invention, a microwave applicator for use in microwave coagulation and ablation therapy includes an insertion (distal) end for insertion into a tissue tract of a living body and an attachment (proximal) end for attachment to a microwave energy source. An antenna is disposed toward the insertion end of the elongated applicator body for radiating microwave energy into the tissue to be treated to generate a desired heating and ablation pattern within the tissue. A coaxial microwave energy transmission line is disposed within the applicator body for conducting microwave energy from the attachment end of the applicator to the antenna. An outer conductive sleeve forms the exterior of a portion of the applicator body and is concentrically spaced around the microwave energy transmission line to form a cooling fluid space between the inner surface of the outer conductive sleeve and the outer surface of the microwave energy transmission line. A guide sleeve is concentrically positioned within this cooling fluid space and is spaced inwardly from the outer conductive sleeve and outwardly around the exterior of the microwave energy transmission line. The guide sleeve directs the flow of circulating cooling fluid along the outer surface of the microwave energy transmission line and the inner surface of the outer conductive sleeve to cool the microwave energy transmission line and the outer conductive sleeve, maintaining the portion of the applicator extending between the outside of the living body and the tissue to be treated within the living body below a temperature that would damage healthy tissue. A temperature sensor is positioned to measure the approximate temperature of the circulating cooling fluid, thereby indicating that cooling fluid is actively circulating within the cooling fluid space and actively cooling the microwave energy transmission line and the outer conductive sleeve during microwave coagulation or ablation treatment. Monitoring the approximate temperature of the cooling fluid can better control tissue heating along the applicator's insertion path into the diseased tissue within the living body, ensuring minimal damage to surrounding normal tissue during treatment. The cooling fluid space extends from the proximal end of the applicator to near the proximal end of the desired heating and ablation zone. Because cooling is not typically required in the tissue to be treated during coagulation and ablation treatment, no cooling is provided in the region of the applicator's radiating antenna where tissue heating is desired.

[0015] In one embodiment of the present invention, a microwave applicator for thermal treatment of diseased tissue in a living body includes a handle for grasping and manipulating the applicator for insertion into the living body. An elongated applicator body having an insertion end for insertion into a tissue tract of the living body typically extends from the handle, forming the attachment end of the applicator. An antenna is located toward the insertion end of the applicator body. Microwave energy is conducted from the handle to the antenna via a microwave energy transmission line in the form of a coaxial cable located within the applicator body. The coaxial cable includes an inner conductor and an outer conductor separated by a dielectric material therebetween. An outer conductive sleeve extends from the handle to its insertion end, which is separated from the conductive tip by a gap typically filled with a dielectric material. To form a substantially smooth, elongated applicator body for insertion into the living body, the outer diameters of the insertion tip, the outer conductive sleeve, and the dielectric material filling the gap therebetween are all approximately equal. The elongated applicator body, or at least the portion thereof that is inserted into the living body, may be coated with a stick-resistant dielectric material, such as Teflon. This may at least partially reduce adhesion of coagulated tissue to the applicator's exterior surface, particularly in the area of ​​tissue coagulation and ablation, facilitating removal of the applicator after treatment. However, in one applicator embodiment, a portion of the dielectric material separating the conductive tip and the outer conductive sleeve remains exposed for direct contact with heated tissue. The dielectric material is a material, such as PEEK (polyetheretherketone), to which heated tissue adheres. Although this is a relatively small area along the applicator, tissue adheres to this dielectric material upon heating, and such adhesion stabilizes the applicator and keeps it in place during tissue treatment. When removal of the applicator is desired, the applicator may be rotated, for example, by a 30° to 45° rotation, to release the tissue and allow removal of the applicator.

[0016] In the illustrated representative embodiment, the elongated applicator body extending from the handle is substantially rigid. The outer conductive sleeve may be made of a material such as stainless steel. The conductive insertion tip of the applicator may also be metal, such as brass or stainless steel, and may be sufficiently sharpened so that the applicator can be inserted directly into the tissue to be treated. However, even when sharpened, the applicator is not inserted directly through the hard tissue of the skin; rather, an incision or opening, typically made by, for example, a hypodermic needle inserted through the skin, must first be made and the applicator then inserted through such incision or opening. Furthermore, in the illustrated representative embodiment, a conductive metal shunt is positioned at the insertion end of the outer conductive sleeve so as to extend toward the insertion tip. The shunt is also electrically coupled to the outer conductor of the microwave energy transmission line, thereby electrically coupling the outer conductor of the microwave energy transmission line to the outer conductive sleeve. The insertion tip is secured to but separated from the insertion end of the shunt by a substantially rigid dielectric spacer, which provides structural rigidity to prevent flexing of the junction between the shunt and tip and electrically insulates the tip, which is electrically coupled to the microwave energy transmission line inner conductor, from the shunt, which is electrically coupled to the microwave energy transmission line outer conductor. The substantially rigid dielectric spacer is bonded to the shunt and applicator tip, for example, by an epoxy adhesive. In another illustrative representative embodiment, no shunt is used and a dielectric material connects the conductive tip to the outer conductive sleeve. In this representative embodiment, the outer conductive sleeve is electrically insulated from both the outer conductive tip and the microwave energy transmission line outer conductor.

[0017] The non-conductive guide sleeve extends from the handle and is concentrically positioned within the elongated applicator, spaced inwardly inside the outer conductive sleeve and spaced outwardly around the outer periphery of the microwave energy transmission line (i.e., outwardly from its outer conductor). The guide sleeve guides a flow of circulating cooling fluid from the handle along the outer surface of the coaxial microwave transmission line to the end of the guide sleeve toward the insertion end of the applicator, and from around the end of the guide sleeve along the inner surface of the outer conductive sleeve to the handle. A reverse flow of cooling fluid may also be used. Circulation of the cooling fluid cools the coaxial microwave transmission line and the conductive sleeve, maintaining the portion of the applicator extending between the outside of the living body and the treated tissue within the living body below temperatures that would damage healthy tissue. A temperature sensor is positioned, for example, in the handle, to measure the approximate temperature of the cooling fluid circulating within the applicator. The temperature of the cooling fluid within the applicator is an indicator of whether the fluid system is operating and whether it is providing sufficient cooling.

[0018] Typically, cooling fluid supply and return connections to a pressurized cooling fluid source through flexible hoses are provided within the handle. Connections to a microwave power source, for example, by flexible coaxial cables, are also provided within the handle. The handle serves as an interface between the more flexible coaxial cables extending from the microwave generator and the more flexible fluid hoses from the cooling fluid source and the substantially rigid, elongated applicator. In one exemplary embodiment, a sheath is provided to enclose and hold together the hoses and flexible coaxial cables extending from the handle, making the applicator easier to handle. An example sheath material is a plastic braided material that tightens around the enclosed hoses and coaxial cables when stretched.

[0019] The temperature sensor used in the applicator may be a thermistor. The resistance of the thermistor changes with the temperature of the thermistor. The temperature measurement taken by the thermistor is obtained by an external circuit that measures temperature by passing a constant direct current through the thermistor. The resistance of the thermistor in turn generates a direct current voltage that is indicative of the temperature of the thermistor. The temperature sensor in the handle, or a temperature sensor positioned along the applicator, may be connected to a flexible coaxial cable that runs from the microwave generator through a coupling network, such as a resistive and capacitive coupling network. The resistive and capacitive coupling network allows direct current to flow from the coaxial cable conductors to the thermistor and from the thermistor to the coaxial cable conductors while isolating the thermistor from the microwave power signal, and allows the microwave power signal to flow to the antenna while isolating the antenna from the direct current. Similarly, a combining network may be used at the opposite end of the flexible coaxial cable, e.g., a power splitting and multiplexing circuit, to separate the DC temperature signals from the flexible coaxial cable conductors and direct them to temperature sensing circuitry in the system controller while isolating the temperature sensing circuitry from the microwave power signal, and to pass the microwave power signal from the system microwave generator while isolating the system microwave generator from the DC temperature signal. Using a computer in the system controller to sense forward power, reflected power, measure thermistor temperature, and possibly monitor other variables, such as monitoring tissue temperature with one or more separately inserted temperature sensors, provides control and feedback for the applied microwave power and proper safety and operation of the microwave coagulation or ablation procedure.

[0020] In addition to a temperature sensor for measuring the approximate temperature of the cooling fluid lines within the applicator, one or more temperature sensors may be positioned along the elongated applicator body to measure the temperature of the tissue of the living body along the applicator. When such additional temperature sensors are provided, it is typically advantageous to position one such temperature sensor at a location near the expected outer edge of the desired or acceptable heating zone of the living tissue that will be heated by the antenna during operation of the applicator. This can be used to provide a warning if the tissue to be protected outside the edge of the treated zone is approaching an undesirably high temperature. This can also be used to estimate the location of the outer edge of the effective heating volume during treatment.

[0021] The use of a phased array can also reduce microwave heating along the applicator shaft due to cross-coupling of energy between antennas driven in phase and separated by a distance, which provides partial power cancellation along the exterior of the inserted applicator and increased tissue heating between these inserted applicators. This partial power cancellation is achieved when the distance between the antennas inserted nearly parallel is approximately half a wavelength, so that the cross-coupled energy is slightly out of phase with the antennas due to their own radiated energy. For example, at a wavelength of 915 MHz, the wavelength in typical tissues with high water content, such as muscle and tumor tissue, is 4.3 to 4.7 cm. This means that for an insertion distance of 2.1 to 2.4 cm, this distance is approximately adequate for this 180° relationship. Cross-coupling phase cancellation also exists at significant phase differences other than 180°; for example, a phase difference of 135° or 225° still provides partial phase cancellation due to cross-coupling of the microwave coupling fields, partially canceling microwave energy along the exterior of the inserted applicator. This corresponds to an applicator spacing of approximately 1.6-3.0 cm in the 915 MHz example. Partial cancellation of microwave power around the inserted shaft results in reduced heating along the inserted shaft during active microwave tissue heating. This also reduces the localized power field locally around the radiating antenna and external shaft, reducing tissue adhesion to the antenna and shaft.

[0022] Control of heating may also include the systematic use of applicators in a phased array with optimization computer guidance in the form of pre-treatment planning to provide an array of applicators with an ideal insertion pattern and power and phase application to generate and control improved homogeneity of power deposition, temperature, and / or coagulation throughout the tumor volume, and particularly in tissue at the tumor margins. Treatment is thus optimized and controlled with the aid of quantitative calculations of either the planned insertion pattern and number of antennas, or the actual pattern shown and achieved by various non-invasive imaging processes, such as computed tomography (CT), ultrasound, or magnetic resonance imaging (MRI). It may also be feasible to use such planning information to adjust the power amplitude and phase of each inserted applicator as directed by a computer-controlled system using predicted power patterns from a computer-based quantitative model.

[0023] In a phased array embodiment of the present invention, a single microwave generator is used to provide microwave power to all applicators. The generator typically operates at 915 MHz, a commonly approved radiation frequency for medical applications. The single generator is connected to a passive, non-switching microwave impedance-matching power splitter (distributor) used to simultaneously direct power to multiple ports connected to one or more microwave dipole antennas, as described with respect to the applicators above. This configuration simultaneously provides approximately equal power to each output connection port. This configuration also provides equal-phase output microwave energy at each output port. Thus, when multiple antennas are connected to the ports of the power splitter, they have equal power and equal phase, and are thus truly referred to as phased array antennas. The cables leading to the radiation points of each antenna are maintained at the same electrical length, so that the radiated energy from the antennas is phase-synchronized and phase-coherent. Phase-synchronized means that there is a fixed phase relationship between the radiation phases of all antennas, and phase-coherent means that the relative radiated phases from each antenna are approximately the same. The use of the described phased array increases heating of the space between the antennas, providing higher power absorption than when using channel switching and other non-phase-synchronous and non-simultaneous channel operation methods, thereby providing improved uniformity of coagulation of the target tissue.

[0024] When using a phased array of applicators, the applicator antennas are inserted in an approximate pattern corresponding to equal spacing along the perimeter of the insertion circle around the tissue to be treated. This provides approximately equal spacing between the antennas along the perimeter of the insertion pattern. Thus, two antennas in a pattern are inserted at a separation that represents the diameter of the insertion circle. Three antennas form a triangular pattern because they are approximately equally spaced around the perimeter of the circular insertion pattern. Four antennas form a square pattern. The antennas should be inserted approximately parallel, with the center points of radiation from each antenna inserted to approximately the same depth relative to the tissue to be treated, and with radiation feed points that are approximately aligned side-by-side.

[0025] As shown, the applicators of the present invention can be used as a single applicator inserted into diseased tissue, or as an array of two or more applicators positioned in or around diseased tissue. To provide the most efficient transfer of microwave energy from the microwave generator to the tissue being treated, the microwave energy transmission path from the microwave generator to the applicator antenna should be impedance-matched and tuned for the number of applicators used. This may require different systems with different power splitters when a single applicator is used, or when multiple applicators are used to form an array. The present invention may provide special power splitter circuits so that a single system can be used for a single applicator or multiple applicators. The present invention provides at least one power splitter circuit for connecting a microwave energy generator to at least one coaxial microwave energy supply cable for supplying microwave energy from the microwave generator to the microwave applicators. At least one power splitter circuit has a microwave power input connected to a microwave generator and a plurality of output ports, one of the plurality of output ports being a single connection output port for use when only a single coaxial microwave energy supply cable and microwave applicator are connected to the power splitter circuit, and the remaining output ports of the plurality of output ports being multi-connection output ports for use when two or more coaxial microwave energy supply cables and microwave applicators are connected to two or more multi-connection output ports of the power splitter circuit. The single connection output port is impedance matched and tuned to provide efficient energy transfer when using a single applicator, and the multi-connection output ports are impedance matched and tuned to provide efficient energy transfer when using a number of applicators between two and the total number of multi-connection output ports provided. In this way, when a single applicator is used, it is connected to the single connection output port.When multiple applicators are used, each of the multiple applicators is connected to a different multi-connection output port, and not to a single output port.

[0026] Means may be provided for detecting whether an antenna is connected to a particular microwave power output port and whether the antenna is connected to the correct port. This may be done when a thermistor or other resistive temperature sensor is used in the applicator, as described above, and a substantially DC temperature sensor signal is transmitted to the system controller through the coaxial power supply cable. In such a case, the system controller may detect which output port an applicator is attached to by detecting whether a temperature sensor signal is present at such output port. By detecting the number of applicators attached to the output ports of the power splitter circuit and which output port they are attached to, the system controller can determine whether a single applicator is connected and, if so, whether it is properly connected to the single-connection output port, or whether two or more applicators are connected and, if so, whether they are all properly connected to the multi-connection output port. The system controller may provide a warning signal if one of multiple applicators is attached to a single-connection output port or if a single applicator is attached to one of multiple applicator output ports.

[0027] Furthermore, when using an arrangement of multiple fluid cooling applicators in which cooling fluid circulates through the applicators, it is necessary to provide a cooling fluid source and return line for the cooling fluid for each applicator. To quickly and easily establish connections for various numbers of applicators, the present invention provides a cooling fluid circulation system adapted to connect to and provide cooling fluid circulation for from a single applicator to multiple applicators, up to a preset number. Such a fluid circulation system of the present invention includes a plurality of cooling fluid supply connectors, each adapted to connect to a separate applicator cooling fluid inlet, and an equal number of cooling fluid return connectors, each adapted to connect to a separate applicator cooling fluid outlet. Each of the plurality of cooling fluid supply connectors includes a normally closed shut-off valve that opens when connected to the applicator cooling fluid inlet. The shut-off valve prevents fluid flow from the cooling fluid supply connector except when connected to the cooling fluid inlet. Each of the plurality of cooling fluid return connectors includes a one-way valve that allows fluid flow only into the cooling fluid return connector. This prevents fluid from flowing out of the system through the cooling fluid return connector, but allows return fluid to flow into the system through such connector when connected to the applicator cooling fluid outlet.

[0028] In this cooling fluid circulation system, when only a single applicator is used, one of the multiple cooling fluid supply connectors is connected to the cooling fluid inlet of the single applicator, and one of the multiple cooling fluid return connectors is connected to the cooling fluid outlet of the single applicator. This provides cooling fluid flow through the single applicator. Cooling fluid does not flow through either the cooling fluid supply connector or the cooling fluid return connector that is not connected to the applicator. When multiple applicators are used, one of the multiple cooling fluid supply connectors is connected to the cooling fluid inlet of one of the multiple applicators, and one of the multiple cooling fluid return connectors is connected to the cooling fluid outlet of one of the multiple applicators. This provides a cooling fluid supply connector connected to each applicator cooling fluid inlet and a cooling fluid return connector connected to each applicator cooling fluid outlet, thereby providing cooling fluid flow through each of the multiple applicators attached to the system. Any number of applicators, up to the number of cooling fluid supply connectors in the fluid supply system, can be connected to the fluid supply system. Additionally, cooling fluid does not flow to either the cooling fluid supply connector or the cooling fluid return connector that is not connected to an applicator.

[0029] An embodiment of the cooling fluid circulation system may also include a cooling fluid reservoir, a pump connected to pump cooling fluid from the cooling fluid reservoir to the plurality of cooling fluid supply connectors, and a fluid conduit connecting the plurality of cooling fluid return connectors to the cooling fluid reservoir to enable fluid flow from the cooling fluid return connectors to the fluid reservoir. The fluid reservoir may conveniently take the form of a standard IV bag filled with sterile saline.

[0030] The narrow separation design between the conductive applicator insertion tip and the insertion end of the outer conductive sleeve provides a zone of high microwave intensity in this space, which can be used to coagulate tissue along the insertion path when microwave power is applied as the microwave antenna is withdrawn from the treatment tissue. This provides coagulation of tissue and vessels that may be present along the insertion path, as well as diseased tissue that may be present along the path, as the applicator is removed from the tissue. By providing regularly spaced depth markings on the elongated applicator and withdrawing the applicator from the tissue in time with a regularly rhythmic sound, a substantially constant rate of removal of the applicator from the tissue can be achieved for effective path ablation. In addition to regularly spaced depth markings, it has also been found advantageous to provide visible warning markings on the exterior of the elongated applicator, located a known distance toward the attachment end of the applicator from the portion of the applicator that will cause tissue ablation (heating zone or ablation zone). As the applicator is withdrawn from the treatment tissue, this warning marking appears to indicate when the zone of pathway ablation or coagulation is approaching the external skin surface, thereby allowing withdrawal of the applicator to be stopped at a desired location short of the skin area to avoid damaging or coagulating tissue within the skin area.

[0031] As shown, a limitation found in current microwave antennas used for microwave coagulation and ablation, particularly applicators operating at 915 MHz, is that the energy distribution pattern generally extends from the proximal end of the desired coagulation and ablation zone around the microwave energy-emitting portion of the applicator toward the proximal end of the applicator and back along the applicator. This undesirably extends the coagulation and ablation zone along the applicator toward the proximal end of the applicator and beyond the tissue desired to be coagulated or ablated. This results in an elliptical or teardrop-shaped heating pattern shape, whereas the desired shape of the energy distribution pattern and coagulation and ablation zone is generally more spherical.

[0032] The inventors theorize that the tail of the heating zone generated by the microwave antenna, caused by microwave energy extending along the applicator from the proximal end of the desired heating zone toward the proximal end of the applicator, and the often continuous extension of this tail along the applicator during application of microwave energy, is caused by tissue drying, initially in the desired heating and ablation zone around the microwave antenna, and then along the body of the applicator from the desired heating zone toward the proximal end of the applicator. The theory is that as the tissue dries around the desired heating zone, the dielectric constant of the tissue decreases, and the wavelength of the microwave energy within the tissue increases. As the wavelength of the microwave energy within the tissue increases, the area heated by the energy increases along the applicator toward the proximal end, causing the longer wavelengths to heat the tissue in this new area. This heating dries the tissue, further extending the wavelength of the microwaves in this region, which further extends the heating region along the applicator shaft and therefore heats more of the tissue along the applicator shaft toward the proximal end of the shaft along the applicator's insertion path. Additionally, or alternatively, as tissue dries and its permittivity value decreases, there is a higher radiated electric field concentrated within the dry tissue surrounding the proximal outer portion of the applicator (this outer portion is typically formed by the metal outer shaft). This is due to the fact that the distribution of the electric field, which is perpendicular to the metal of the metal shaft and inversely proportional to the corresponding tissue permittivity value, changes with the boundary between wet and dry tissue. This means that the electric field lines passing perpendicularly through the dry tissue layer to the perpendicular metal shaft change in their distribution relative to the tissue. For example, a ten-fold decrease in the dielectric constant value of the tissue surrounding the shaft (as may occur due to carbonization) results in a ten-fold increase in electric field strength in this dry, carbonized area, which does not decay as rapidly as it would in non-dried tissue as it propagates along the outer metal body of the applicator toward the proximal end, which may further increase the length of the tapered tail of the tissue heating or ablation zone along the proximal body portion of the applicator.

[0033] The inventors have discovered that by supplying a fluid, such as saline solution, to tissue along the applicator shaft extending from approximately the proximal end of the desired heating zone toward the proximal end of the applicator to displace fluid in such tissue and prevent such tissue from drying out, the tail of the heating zone is limited and does not increase with increasing heating time, but remains substantially constant. Thus, by injecting fluid into tissue along the applicator shaft extending from near the proximal end of the desired heating zone toward the proximal end of the applicator, the tissue in this region maintains its wetness or moisture content, limiting the distance the tail extends along the applicator and substantially preventing continued elongation of the tail during heating. As a result, the heating and ablation zone tends to be less teardrop-shaped and more spherical. This occurs despite not requiring the injection of fluid into the desired heating zone, which would otherwise cause the tissue in the desired heating zone to dry out during heating. By injecting fluid into the tissue outside the desired heating zone and in the region shown proximally, the applicator can be designed and adjusted to produce a substantially consistent heating and ablation zone. Fluid can be delivered to the tissue in a variety of ways. If the applicator includes an applicator fluid cooling system, the fluid injected into the tissue can be a portion of the cooling fluid from the applicator cooling system that is directed from the cooling system to the tissue, or fluid can be provided directly to the tissue specifically to keep it moist, with or without a fluid cooling system.

[0034] For example, as described with respect to illustrated embodiments of the present invention, when using an applicator having a cooling system that circulates a cooling fluid through the applicator, if fluid infusion into tissue is desired, the outer conductive sleeve and / or shunt may include one or more openings therethrough to allow a portion of the cooling fluid to flow from the applicator as it circulates within the applicator into the tissue surrounding the applicator adjacent to the proximal end of the desired heating and ablation zone created by the applicator and extending a fixed distance from the desired heating and ablation zone toward the proximal end of the applicator. The one or more openings may be sized and positioned to allow a substantially predetermined amount of fluid to flow into the tissue while the fluid circulates within the applicator to maintain moisture within the tissue during operation of the applicator.

[0035] Furthermore, as indicated, depending on the size and shape of the mass of diseased tissue being treated, the use of 2450 MHz may be advantageous in some situations and 915 MHz in other situations. In a further embodiment of the present invention, a microwave ablation system includes both a 915 MHz microwave generator and a 2450 MHz microwave generator with a common power source and a common control system to provide output connections for an applicator adapted to apply microwaves at the 2450 MHz frequency to the tissue being treated and / or one or more applicators adapted to apply microwaves at the 915 MHz frequency to the tissue being treated. The system may, for example, provide one or the other frequency selected for a particular treatment procedure, or may be adapted to provide output at both frequencies simultaneously, or may be multiplexed to provide both frequencies substantially simultaneously or timed so that one frequency is provided for a predetermined time interval and the other frequency is provided for a subsequent predetermined time interval. Such a system can provide for the use of either 915 MHz microwaves or 2450 MHz microwaves during different treatment procedures, or can provide both 915 MHz microwaves and 2450 MHz microwaves during the same treatment procedure, all under common control from a single operating system.

[0036] Other features of the present invention will be more readily understood from the following detailed description taken in conjunction with the drawings, which illustrate the best mode presently contemplated for carrying out the invention. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 2 is a side view of an applicator according to an embodiment of the present invention. [Figure 2] 2 is a vertical cross-sectional view of a portion of the applicator of FIG. 1; [Figure 3] FIG. 3 is a perspective, partially cut-away view of a portion of the applicator of FIG. 2; [Figure 4] 2 is a vertical cross-sectional view of the handle portion of the applicator of FIG. 1. [Figure 5] 5 is a schematic diagram of the electrical connections within the handle portion of the applicator shown in FIG. 4. [Figure 6] FIG. 10 is a partially cutaway perspective view of another embodiment of the handle of the applicator of the present invention. [Figure 7] 1 is a block diagram of a system for microwave therapy using the applicator of the present invention. [Figure 8] FIG. 10 is a block diagram of a power splitter and multiplexer for use in the system of the present invention when using an arrangement of multiple applicators. [Figure 9] FIG. 2 is a side view of the applicator shown in FIG. 1 showing additional depth markings along the applicator. [Figure 10] 3 is a vertical cross-sectional view similar to that of FIG. 2 of a different embodiment of the applicator of the present invention; [Figure 11] 1 is a schematic diagram of a cooling fluid circulation system of the present invention. [Figure 12] 1 is a computer-generated representation of the heating pattern produced by an applicator of the present invention, where the tissue along the proximal end of the applicator is desiccated and charred. [Figure 13]A computer-generated representation, similar to that of Fig. 12, of the heating pattern produced by the same applicator of the present invention as used in Fig. 12, with fluid being injected into the tissue along the proximal end of the applicator to limit desiccation and charring of the tissue. [Figure 14] 11 is a vertical cross-sectional view similar to that of FIG. 10 of a different embodiment of an applicator of the present invention having a fluid injection port. [Figure 15] 3 is a vertical cross-sectional view similar to that of FIG. 2 of a different embodiment of an applicator of the present invention having a fluid injection port. [Figure 16] 15 is a vertical cross-sectional view similar to that of FIGS. 10 and 14 of a different embodiment of an applicator of the present invention having a fluid injection port and no cooling fluid return path. [Figure 17] 16 is a vertical cross-sectional view similar to that of FIGS. 2 and 15 of a different embodiment of an applicator of the present invention having a fluid injection port and no cooling fluid return path. [Figure 18] 19 is a schematic diagram of a cooling fluid circulation system of the present invention similar to FIG. 11 but without the fluid return line and connector and usable with the applicator of FIGS. 17 and 18. [Figure 19] 19 is a schematic diagram of a cooling fluid circulation system of the present invention that does not have a fluid return line, fluid return connector, and fluid pump, and that can be used with the applicator of FIGS. 17 and 18. FIG. [Figure 20] 1 is a block diagram illustrating an embodiment of a dual frequency ablation system of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] Reference will now be made to and specific terminology will be used herein to describe the exemplary embodiments illustrated in the drawings. It will be understood, however, that no limitation of the scope of the invention is intended thereby. Alterations and further modifications of the features of the invention exemplified herein, and additional applications of the principles of the invention exemplified herein, which occur to those skilled in the art and possessor of this disclosure, are deemed to be within the scope of the invention.

[0039] One embodiment of a microwave applicator of the present invention for microwave coagulation and ablation treatment of diseased tissue within a living body is illustrated in Figure 1. The applicator, generally designated 10, includes a handle 12 from which extends a substantially rigid, elongated applicator body 14, with an insertion tip 16 forming the insertion end of the applicator for insertion into a tissue tract of a living body. The substantially rigid, elongated applicator body 14 includes an outer conductive sleeve 18 extending from the handle 12, a conductive shunt 20, the conductive insertion tip 16, and a dielectric collar 22 positioned between the insertion tip 16 and the shunt 20. As shown in the figure, the dielectric collar 22 joins the conductive insertion tip 16 to the shunt 20 and, through the shunt 20, to the outer conductive sleeve 18. The outer diameters of the outer conductive sleeve 18, the conductive shunt 20, the dielectric collar 22, and the exposed portion of the insertion tip 16 (which may be sharpened at its insertion end 17) are all approximately equal to form a smooth, continuous, elongated applicator body for insertion into biological tissue. The elongated applicator body may be coated with a stick-resistant dielectric material such as Teflon (not shown). A pistol grip 24 allows for easy grasping of the handle for operation of the applicator.

[0040] The applicator has a microwave antenna portion 25 toward the insertion tip of the elongated applicator body 14, which radiates microwave energy from the antenna portion to the biological tissue. Microwave energy is transmitted from the handle 12, through the elongated applicator, and to the antenna portion by a coaxial microwave transmission line 26 (FIGS. 2-4) within the elongated applicator body and having an inner conductor 29 and an outer conductor 27 separated by a dielectric material 28 positioned therebetween. Although not required, the coaxial transmission line 26 can be a semi-rigid coaxial cable having copper inner and outer conductors and Teflon or Teflon and air dielectric materials. No outer dielectric insulating material is used. Such coaxial cables typically have an impedance of approximately 50 Ω, which provides a good impedance match to the microwave generator and typical biological tissue characteristics.

[0041] The outer diameter of the coaxial transmission line (and the outer diameter of the coaxial transmission line's outer conductor 27) is smaller than the inner diameter of the outer conductive sleeve 18, thereby providing a space 82 between the transmission line and the outer conductive sleeve. This space is referred to as the cooling fluid space. The conductive shunt 20 is positioned around and in electrical contact with both the insertion end 83 of the transmission line outer conductor 27 and the outer conductive sleeve 18. The shunt 20 includes a smaller outer diameter end 84 toward the handle end of the applicator that is sized to fit into the space 82 between the outer surface of the outer conductor 27 of the coaxial transmission line 26 and the inner surface of the outer conductive sleeve 18. The shunt 20 may be soldered to both the outer conductor 27 and the outer sleeve 18 to ensure a good electrical connection. The soldering also secures the shunt 20 to the outer sleeve 18 for a strong connection between the shunt 20 and the sleeve 18. However, the shunt 20 may be secured to the sleeve 18, and optionally to the outer conductor 27, with a bonding agent such as an epoxy adhesive material. If the bonding agent is conductive, this may replace soldering. With this connection, the shunt 20 closes or blocks the cooling fluid space 82 toward the insertion end 85 of the outer conductive sleeve 18.

[0042] The shunt 20 extends beyond the actual end 86 of the outer conductor to form a larger inner diameter shunt portion 87. The insertion end of the larger diameter shunt portion 87 can receive a smaller outer diameter mounting end 88 of the applicator tip 16, which has a dielectric collar 22 thereon. The dielectric collar 22 fits over the smaller outer diameter mounting portion 88 of the applicator tip 16, and itself has a smaller outer diameter insertion portion 89 that fits within the larger inner diameter shunt portion 87. This interfitting configuration creates a strong connection of the tip to the rest of the applicator, with the dielectric collar 22 being bonded to the tip and shunt by an adhesive material such as epoxy.

[0043] A dielectric collar 22 positioned between the shunt 20 and the tip 16 electrically insulates the tip 16 from the shunt 20 and from the outer conductive sleeve 18. The shunt 20 is electrically connected to the outer conductor 27 of the coaxial transmission line 26, such that the shunt 20 is an extension of the outer conductor 27, and the insertion end 90 of the conductive shunt 20 is the effective insertion end of the outer conductor 27. The inner conductor 29 of the coaxial transmission line extends toward the insertion end of the applicator, beyond the insertion end 91 of the coaxial transmission line dielectric material 28, to an inner conductor insertion end 92. However, both the insertion end 91 of the coaxial transmission dielectric material and the insertion end 92 of the coaxial transmission inner conductor are within the larger inner diameter shunt portion 87 of the shunt 20 and do not extend beyond the insertion end 90 of the shunt 20.

[0044] The smaller radius mounting end 88 of the applicator tip 16 also includes a tip tab 93 that extends therefrom toward the handle end of the applicator and toward the insertion end 91 of the coaxial transmission line dielectric 28. The tip tab 93 is positioned so that the extension of the coaxial transmission line inner conductor 29 beyond the end 91 of the coaxial transmission line dielectric 28 abuts the tip tab 93 and can be secured in electrical contact by soldering. In this configuration, the inner conductor 29 does not extend into the tip 16 but is merely abutted and electrically connected to the tip tab 93.

[0045] In construction, the outer conductive sleeve 18 may be made of a metallic material such as stainless steel, the conductive tip and shunt may be formed of a metallic material such as brass or stainless steel, and the dielectric insulating collar may be formed of a substantially rigid plastic material. All such parts may be bonded using an epoxy resin. Furthermore, while the configuration described with respect to this illustrated embodiment provides an embodiment of a microwave antenna facing toward the applicator insertion end, various other applicator configurations may be used to form the microwave antenna facing toward the applicator insertion end. For example, FIG. 10 illustrates another embodiment of an applicator insert in which a shunt is not used. As shown in FIG. 10, the conductive applicator insertion tip 16 is directly connected to the outer conductive sleeve 18 by a dielectric collar 22, which electrically insulates the conductive applicator insertion tip from the outer conductive sleeve 18. The end of the dielectric collar 22 toward the mounting end of the applicator extends into the space 82 between the outer conductive sleeve 18 and the outer conductor 27 of the coaxial microwave transmission line 26, electrically insulating the outer conductive sleeve 18 from the outer conductor 27. In this embodiment, the outer conductive sleeve 18 is not electrically connected to the outer conductor 27. The dielectric collar 22 also defines the end of the cooling fluid space 82 toward the insertion end of the applicator. Similar to the configuration shown in FIG. 2, the insertion tip 16 includes a tip tab 93 that is coupled to the inner conductor 29. The antenna and insertion end configuration of the applicator has also been found to work well for use in the present invention.

[0046] As shown in FIG. 1 , an elongated applicator body 14 extends from the handle 12. As shown in FIG. 4 , an outer conductive sleeve 18 is secured within the forward portion 13 of the handle body 15 and within the forward end of a cooling fluid reservoir 38, which is mounted within the handle body 15. The cooling fluid reservoir 38 includes two reservoir chambers 34 and 36 separated by a guide sleeve 40 that extends from its connection with the reservoir bulkhead 35 to and within the outer conductive sleeve 18 toward the insertion end of the applicator. The guide sleeve 40 may be a thin-walled plastic sleeve made of a polyimide plastic such as Kapton. Attachment of the outer conductive sleeve 18 to the handle body 15 and fluid reservoir 38, and of the guide sleeve 40 to the reservoir bulkhead 35, may be by adhesive, epoxy, or other bonding agent. The coaxial transmission line 26 extends through the cooling fluid reservoir 38 and into the guide sleeve 40. The coaxial transmission line 26 extends the entire length of the guide sleeve 40, past the guide sleeve insertion end 41 (FIG. 2), and into the shunt 20.

[0047] 2 and 4, the guide sleeve 40 extends into a cooling fluid space 82 between the outside of the coaxial transmission line 26 and the inside of the outer conductive sleeve 18. The guide sleeve 40 divides the cooling fluid space 82 along the length of the guide sleeve 40 within space 82 into an inner cooling fluid space 42 and an outer cooling fluid space 43. The inner cooling fluid space 42 is formed between the outer surface of the coaxial transmission line 26 and the inner surface of the guide sleeve 40, and the outer cooling fluid space 43 is formed between the outer surface of the guide sleeve 40 and the inner surface of the outer conductive sleeve 18. The reservoir chamber 34 communicates with the inner cooling fluid space 42, and the reservoir chamber 36 communicates with the outer cooling fluid space 43.

[0048] While either reservoir 34 or 36 can be a cooling fluid inlet or a cooling fluid outlet, it has been found that for ease of temperature sensor placement, as described with respect to the location of temperature sensor 60, reservoir chamber 34 can be a cooling fluid inlet reservoir and reservoir 36 can be a cooling fluid outlet reservoir. In such a case, cooling fluid to the applicator flows from a cooling fluid source (not shown) through tubing 30 to reservoir chamber 34. From reservoir chamber 34, cooling fluid flows through interior cooling fluid space 42 and along the outer surface of coaxial transmission line 26, cooling the outer surface of coaxial transmission line 26. As previously shown with respect to FIG. 2 , cooling fluid space 82, into which guide sleeve 40 extends, is blocked at the insertion end of outer conductive sleeve 18 by smaller diameter portion 84 of shunt 20, which fits within and blocks the insertion end of space 82. 2, the insertion end 41 of the guide sleeve 40 terminates short of the end of the space 82 formed by the shunt 20, leaving an undivided fluid space portion connecting the inner cooling fluid space 42 and the outer cooling fluid space 43. Thus, when cooling fluid flowing in the inner cooling fluid space 42 toward the insertion end of the applicator reaches the insertion end 41 of the guide sleeve 40, it flows into the undivided space 82 around the insertion end 41 of the guide sleeve 40, into the outer cooling fluid space 43, along the inner surface of the outer conductive sleeve 18, back into the reservoir chamber 36, and out the fluid outlet tube 32, where it can flow either back to the fluid source for cooling and recirculation or to a fluid drain tube.

[0049] As shown in FIG. 4 , microwave energy is provided from a microwave generator (not shown) to the applicator by a coaxial microwave energy supply cable 46, which provides a path for microwave energy from the generator to the applicator. The coaxial microwave energy supply cable 46 is typically a flexible 50 Ω coaxial cable including an inner or center conductor 48, an outer conductor 49, and a dielectric spacer 50 therebetween. In the illustrated embodiment, the connection between the flexible coaxial microwave energy supply cable 46 and the semi-rigid coaxial transmission line 26 is provided through coupling circuitry on a printed circuit card 58 that supports small chip capacitors and resistors (a schematic diagram of the circuit in FIG. 4 ; see also FIG. 5 ). The coaxial microwave energy supply cable center conductor 48 is connected by a conductive metal trace 51 on the circuit board 58 to a capacitor 52, which is connected to the inner conductor 29 of the coaxial transmission line 26. The coaxial microwave energy supply cable outer conductor 49 is connected by a conductive element or wire 47 to a conductive metal path 53 on the circuit card 58, which is connected to the outer conductor 27 of the coaxial transmission line 26. This provides a direct path for microwave current to flow between the outer conductors. The circuit diagram of Figure 5 shows a capacitor 55 connected between the two outer conductors 49 and 27; although this is not necessary and is not shown in Figure 4, it may be advantageous to include it to provide further isolation of the microwave antenna from the DC current in the flexible coaxial microwave energy supply cable 46.

[0050] A temperature sensor in the form of a thermistor 60 is disposed on and coupled to the outer conductive sleeve 18, so that it is at approximately the same temperature as the outer conductive sleeve 18. When positioned in the position shown in FIG. 4, the thermistor 60 measures the temperature of the outer conductive sleeve 18 around its handle end, which is approximately the temperature of the cooling fluid after it has flowed through the elongated applicator body 14. The thermistor 60 can be positioned in other locations that allow it to indicate the approximate temperature of the cooling fluid after or during its flow through the applicator. When positioned as shown, the thermistor 60 measures the approximate temperature of the cooling fluid between the guide sleeve 40 and the outer conductive sleeve 18 as the cooling fluid returns to the cooling fluid discharge reservoir chamber 36 after flowing through the inner cooling fluid space 42 and the outer cooling fluid space 43. At this position, the cooling fluid has reached approximately its maximum temperature. The thermistor 60 can be positioned within the cooling fluid itself, such as in the cooling fluid discharge reservoir chamber 36, if desired. The function of this thermistor 60 is to provide an indication that cooling fluid is actually flowing through the applicator each time microwave power is applied. During application of microwave energy, the microwave energy causes self-heating of the coaxial transmission line 26 within the applicator. This increases the temperature of the coaxial transmission line 26, thereby heating the surrounding area between the thermistor 60 and the coaxial transmission line 26. Without circulation of cooling fluid, the applicator outer conductive sleeve 18 could reach temperatures that could damage normal tissue. The flow of cooling fluid within the applicator, along the coaxial transmission line 26 and the outer conductive sleeve 18, removes much of this generated heat, thereby keeping the thermistor 60 cooler when cooling fluid is flowing than when fluid flow is absent. When fluid flow is stopped or restricted, the fluid heats up to a higher temperature than when proper flow is present. When proper flow is present, the applicator outer conductive sleeve 18 remains below a temperature that would damage tissue.

[0051] A thermistor is a resistive electrical device that changes resistance depending on its temperature. Two wires 62a and 62b from the thermistor 60 are connected through a capacitor 56. Wire 62a connects to the capacitor 56 and also directly to the outer conductor 49 of the flexible coaxial cable 46. Wire 62b is attached to the other side of the capacitor 56 and to one side of the resistor 54 through a conductive metal path 57. The other side of the resistor 54 is connected to the conductive metal path 51 through a wire or conductive metal path 59. Thus, the thermistor 60 is electrically connected between the inner conductor 48 and the outer conductor 49 of the flexible coaxial cable 46. This allows the resistance of the thermistor 60 to be monitored by a direct current that flows from the center conductor 48 through the conductive metal traces 51 and 59 to the resistor 54, through the conductive metal traces 57 and wire 62b to the thermistor 60, and back to the outer conductor 49 of the flexible coaxial cable 46 via wire 62a and wire 47. Capacitor 52 prevents DC current from flowing in the inner conductor 29 of coaxial transmission line 26, thereby preventing DC current from flowing through the applicator antenna and the tissue into which the applicator is inserted. If capacitor 55 is provided in the circuit, it prevents DC current from flowing in the outer conductor 27 of coaxial transmission line 26, further ensuring that DC current does not flow through the antenna and the tissue into which the applicator is inserted. The described circuit allows the flexible coaxial microwave energy delivery cable to serve a dual purpose. DC current for monitoring the resistance of the thermistor 60 flows through the flexible coaxial microwave energy delivery cable 46 along with the microwave energy flowing through the flexible coaxial microwave energy delivery cable 46 from the microwave energy generator to the applicator. In the described configuration, a temperature-indicative signal is transmitted between the thermistor and the system controller through the same two coaxial cable conductors 48 and 49 that transmit microwave power from the microwave generator to the applicator. This eliminates the need for a separate additional wire from the handle to transmit the temperature signal from the thermistor to the system controller.

[0052] As shown, the signal from thermistor 60 provides the system controller with an indication of the temperature of the cooling fluid circulating within the outer conductive sleeve and applicator. Upon application of microwave power to the applicator, which causes heating of the coaxial transmission line 26, the temperature of thermistor 60 remains low as long as the cooling fluid is properly flowing within the applicator. If, for any reason, the cooling fluid stops flowing or is restricted within the applicator, the coaxial transmission line 26 will begin to heat up, and the temperature of the outer conductive sleeve 18 and any non-flowing or slowly flowing fluid within the applicator will also increase. This will increase the temperature of thermistor 60. This increase in the measured temperature of thermistor 60 provides an indication that the cooling fluid is not properly flowing, and the system controller can activate an alarm or other corrective action.

[0053] Figure 6 shows a partially cutaway perspective view of a handle similar to that of Figure 4, but with a slightly differently configured body 45 and a different arrangement of the inlet and outlet tubes 30 and 32 from the reservoir chambers 34 and 36. However, the configuration of the handle components is substantially the same, and the components are numbered the same as in Figure 4. The wires from the thermistor 40 are not shown. Figure 6 provides a better illustration of the actual configuration of the applicator handle.

[0054] As can be seen from the above description, in addition to providing a way for the applicator to be grasped and manipulated for insertion into a living body, the handle 12 also serves as an interface between the substantially rigid applicator body 14 and the flexible coaxial microwave energy supply cable extending from the microwave generator to the applicator, provides for the insertion of a temperature signal into the flexible coaxial microwave energy supply cable, and serves as an interface between the flexible fluid hose from or to the cooling fluid source and the cooling fluid reservoir. Various configurations of the handle can be used. While the flexible coaxial microwave energy supply cable and flexible fluid hose are shown as extending from the end of the handle grip (and may be enclosed within a sheath, if desired), connectors may be provided directly on the handle, whereby the flexible coaxial microwave energy supply cable, and consequently the flexible fluid hose, are also detachable from the handle. In the embodiment shown in FIG. 4 , the flexible coaxial microwave energy delivery cable 46 and flexible fluid hoses 30 and 32 are shown coming together in a side-by-side relationship in the handle 12 and entering a sheath 154 that extends outward from the end of the pistol grip 24 to keep the cables and hoses together for a distance extending from the handle. This allows for easier manipulation of the applicator during use. The hoses 30 and 32 and the cable 46 extend from the end 156 of the sheath 150, with the hoses terminating in hose connectors 158 and 160 adapted for connection to cooling fluid supply and return hose connectors. The coaxial cable 46 terminates in a cable connector 162 adapted to connect to an additional microwave energy delivery cable. A variety of materials can be used for the sheath 154. A plastic braided material, which acts like the old "Chinese handcuffs" that tighten around the enclosed cable and hose, has been found to work well because it provides a good outer covering that improves handling and storage of the applicator, and also because it easily transfers heat generated by the coaxial cable.

[0055] FIG. 7 is a functional block diagram of the basic system of the present invention described above, using a single applicator, for patient treatment. An operator interface 61, e.g., a computer screen and keyboard or a simple touch screen, is provided for system control and display and monitoring of the treatment procedure. The user interface is connected by cable 63 to a system controller 64, e.g., a computer processor. The controller provides control and monitoring of a microwave generator 68 through cable 66. The generator 68 includes a microwave oscillator, and the power amplitude, including measurements of both forward and reflected power, at the output of the generator 68 can be controlled and monitored by the controller 64. The generated microwave power is then directed by a transmission line cable 70, e.g., a coaxial cable, to a multiplexer and power splitter circuit 74. The microwave path within the multiplexer and power splitter circuit 74 includes an impedance-matched microwave path that directs microwave power to the applicator 10, which has an elongated applicator body 14, via a flexible coaxial microwave energy supply cable 72. As described, within the applicator 10, there is a DC path that flows through a temperature-sensing thermistor, which also allows DC to flow through the coaxial microwave energy delivery cable 72. The DC used to measure the temperature within the elongated body 14 of the applicator is separated from the microwave power signal in the multiplexer portion of the multiplexer and power splitter circuit 74 and transmitted along a DC circuit path 76 directed to a temperature monitoring circuit 78. The temperature monitoring circuit 78 then returns a temperature signal over cable 80 to the controller 64, allowing the controller to monitor and control the microwave power level generated by the microwave generator 68 and to limit the microwave power delivered to the applicator if an excessive temperature is measured at the applicator 10. The temperature monitoring circuit 78 may be part of the controller 64.

[0056] In many cases, it is desirable to provide patient treatment using a phased array of applicators rather than a single applicator. When using a phased array, multiple applicators are inserted into the patient in a generally parallel arrangement in a generally evenly spaced pattern along the periphery of an insertion circle around the tissue to be treated. Each applicator should be inserted so that its radiating antennas are positioned at approximately the same depth relative to the tissue to be treated in order to have radiation delivery points that are generally aligned side-by-side. The use of multiple applicators in a phased array generally allows for better control of the applicators, producing more uniform power deposition, temperature, and / or tissue coagulation than when using a single applicator, throughout the tumor volume to be treated, and particularly at the tumor border. The use of a phased array can also reduce microwave heating along the applicator shaft due to cross-coupling of energy between antennas driven in phase and separated by a distance, which provides partial power cancellation along the exterior of the inserted applicators and increased tissue heating between these inserted applicators. With a phased array, pre-treatment planning can be used to provide an array of applicators with ideal insertion patterns and power and phase application to generate and control the desired heating. Treatment can then be optimized and controlled with the aid of quantitative calculations of either the planned insertion pattern and number of antennas, or the actual pattern achieved as shown by various non-invasive imaging processes, such as computed tomography (CT), ultrasound, or magnetic resonance imaging (MRI). The power amplitude and phase of each inserted applicator can be adjusted under the direction of a computer-controlled system using the power pattern predicted from the computer's quantitative model. Additionally, actual temperature measurements can be taken and compared to the predicted power pattern and predicted temperature, allowing the system to compensate for errors.

[0057] In a phased array embodiment of the present invention, a single microwave generator is used to provide microwave power to all applicators. The generator typically operates at 915 MHz, a commonly approved radiation frequency for medical applications. The single generator is connected to a passive, non-switching microwave impedance-matching power splitter (distributor) used to simultaneously direct power to multiple ports connected to one or more microwave dipole antennas, as described with respect to the applicators above. This configuration simultaneously provides approximately equal power to each output connection port. This configuration also provides equal-phase output microwave energy at each output port. Thus, when multiple antennas are connected to the ports of the power splitter, they have equal power and equal phase, and are thus truly referred to as phased array antennas. The cables leading to the radiation points of each antenna are maintained at the same electrical length, so that the radiated energy from the antennas is phase-synchronized and phase-coherent. Phase-synchronized means that there is a fixed phase relationship between the radiation phases of all antennas, and phase-coherent means that the relative radiated phases from each antenna are approximately the same. Because different array patterns are desirable for different optimized treatments, and the desired treatments may use a single applicator or a different number of multiple applicators, it is desirable to have a system that can drive and monitor either a single applicator or multiple applicators. However, current systems are typically designed to optimize power delivery to either a single applicator or a fixed number of multiple applicators. This does not provide the flexibility desired for configuring different arrays using a single delivery system. In an array power system, it is desirable to have an indication as to whether there is an antenna connected to a particular microwave power output port, and whether the antenna is connected correctly.

[0058] FIG. 8 shows an embodiment of a multiplexer and power splitter circuit according to the present invention, which provides for the isolation of temperature signals from microwave power signals for multiple applicators and may provide for optimization of single, two, or three applicator installations. The microwave power signal from a microwave generator (not shown) is supplied to the multiplexer and power splitter through a coaxial cable 100, typically 50 Ω impedance. The multiplexer and power splitter circuit is typically on a printed circuit card made from a low-loss dielectric material, such as a Teflon-based material, with a ground plane on one side and the circuit shown in FIG. 8 representing the conductive paths forming the various transmission lines on the other side. The input microwave power signal connects to an input in the form of a conductive patch 102, which provides the power-splitting section. This directs the microwave power into four paths: one path indicated by path 104 and three identical paths indicated by path 114. Along path 104 is a chip capacitor 106, which conducts microwave current but blocks DC, preventing it from reaching the power splitter patch 102. Input microwaves flow through capacitor 106 and along transmission line 108 to circuit output port 110. Transmission lines 104 and 108 are 50 Ω transmission lines, both of which have a 180° electrical length delay at the microwave operating frequency. Capacitor 106 has a low impedance, typically less than 2 ohms reactive impedance, to avoid transmission line mismatch. It then directs microwave power from input transmission line 100 to circuit output port 110. Output port 110 forms an output port for connection of a single applicator antenna through a 50 Ω impedance coaxial microwave energy delivery cable attached to output port 110. This output port 110 is used only when a single antenna is connected to the multiplexer and power splitter circuit and is sometimes referred to herein as the single-connection output port.

[0059] The power splitter conductive patch 102 is also connected to three other identical transmission lines, each having a microwave input section 114 with a series chip capacitor 112 along its path, and a microwave output section 116. Like capacitor 106, each capacitor 112 in the microwave input section has a low impedance, typically less than 2 Ω of reactive impedance, allowing microwave current to flow but blocking the flow of DC, preventing DC from reaching the power splitter patch 102. The entire length of the microwave input section of the transmission line from the power splitter conductive patch 102 through the capacitors 112 along path 114 is approximately 90° lag at microwave frequencies. Additionally, the characteristic impedance of the microwave input section of the transmission line 114 with capacitors 112, from the power splitter conductive patch 102 to the end of path 114, typically 70-90 Ω, is used to provide an impedance matching section for the input when two or three applicators are connected to multiple connector output ports 118. The microwave output sections 116 are 50 Ω sections that connect the lines 114 to the multi-connection output ports 118, and are long enough to delay the microwave signal by approximately 90°. The 50 Ω impedance of the microwave output sections 116 provides an impedance match for the flexible coaxial microwave energy delivery cable and applicator connected to the output ports 118.

[0060] The described power splitter circuit forms an impedance-matched microwave power splitter that is solely connected to the single-connection output to port 110 when a single applicator is used. In this case, the other three output ports (respectively, multi-connection output ports 118) are not connected to an applicator. The path length from the power splitter conductive path 102 to each of these multi-connection output ports 118 is 180°. Microwave power propagating to these multi-connection output ports 118 would be completely reflected back if no connection existed at the port, and this reflected power would be reflected at the same phase angle as the power entering these ports because this is an open line termination. This means that the overall phase delay of the power traveling from the power splitter conductive patch 102 to the multi-connection output port 118 and back to the power splitter conductive patch 102 is 360°. This inherent phase delay, in turn, presents the power splitter with an open circuit. The open ports 118 therefore make these paths tuned paths, which do not reflect power reaching the input line 100 and direct all power only to the single connection output port 110, the single applicator connected to output port 110, for efficient power transfer to the single applicator.

[0061] When two or three applicators are connected to the corresponding multi-connection output port 118, no applicator is connected to port 110. The path delay between the power splitter conductive patch 102 and the output port 110 is also 180°. The delay to the output port 110 and back to the conductive patch 102 is 360°. If no applicator is attached to the single-connection output port 110, it still becomes a tuned path for microwave energy. As a result, the microwave multiplexer and power splitter circuit is an impedance-matching splitter that automatically directs power to one, two, or three applicators. Attaching only a single applicator to one of the multi-connection output ports 118 is not permitted because doing so would create an impedance mismatch and result in unacceptable reflected power back to the input line 100. Also, if no applicators are connected to any of the power splitter's ports, the entire transmission path is open-circuited. This allows multiple power splitter circuits to be used to provide more than four applicators if needed. For example, if two power splitter circuits are used, anywhere from one to six applicators can be connected to the system.

[0062] The multiplexer and power splitter circuit also includes inductive coils or chokes 120, 122, 124, and 128 connected to transmission lines 104 and 114, respectively. Each of these inductive coils, designated 128, 130, 132, and 134, is connected via capacitance to grounded chassis. These capacitors and inductive coils filter microwave signals from passing to temperature sensing ports 136, 138, 140, and 142, but pass DC signals from transmission lines 108 and 114 to these temperature sensing ports. These temperature sensing ports are connected to a temperature monitoring circuit, and ultimately to a system computer or controller, which detects the measured resistance of thermistors connected to the applicators' two-wire coaxial microwave energy supply connectors. These DC temperature sensing signals from the applicators to the temperature sensing ports provide the system controller with measurements of the temperatures measured by the temperature sensors within each applicator.

[0063] These DC temperature sensing signals from the applicators to the temperature sensing ports also provide the system controller with a measurement as to whether an applicator is connected to a particular output port of the multiplexer and power splitter circuit. If an applicator is connected to a particular multiplexer and power splitter circuit output port, such as output port 110, a temperature signal will be present on temperature sensing port 136. The system controller then knows that an applicator is connected to output port 110. Similarly, if temperature signals are present on temperature sensing ports 138 and 142, the system controller knows that two applicators are connected to two of multi-connection output ports 118 and can identify which two output ports have applicators connected to them. If the system controller senses temperature signals at temperature sensing ports 136 and 138, the system controller knows that two applicators are connected to the multiplexer and power splitter circuit, but the applicators are not properly connected; one of the two applicators is improperly connected to single-connection output port 110, while the other of the two applicators is properly connected to one of the multi-connection output ports 118. The system controller can then provide a warning signal to the system user indicating that the applicators are improperly connected and that the applicator connected to single-connection output port 110 should be removed and connected to one of the multi-connection output ports 118. The use of this special multiplexer and power splitter circuit, in addition to providing an indication that the appropriate number of applicators are connected to the correct output ports for efficient and desired microwave power delivery to the connected applicators, also allows for measurement of applicator cooling temperatures to determine proper fluid flow within each connected applicator to protect normal tissue.

[0064] If temperature sensing is not required, but sensing the attachment of a microwave applicator to the power splitter circuit is desired, a thermistor or other temperature sensor providing a DC temperature signal can be replaced with a conventional resistor, which will provide a DC signal in substantially the same manner as a thermistor to indicate that a microwave applicator is attached to a power splitter output port and to which port the applicator is attached. This use of a resistor is considered equivalent to a thermistor or other temperature sensor providing a DC temperature sensor signal for purposes of applicator detection.

[0065] Another consideration when using an arrangement of multiple fluid cooling applicators, in which cooling fluid circulates through the applicators, is the need to provide a cooling fluid source and return line for the cooling fluid for each applicator. To quickly and easily establish connection for various numbers of applicators, the present invention provides a cooling fluid circulation system adapted to connect and provide cooling fluid circulation to anywhere from a single applicator to a pre-defined number of applicators. Referring to FIG. 11 , the cooling fluid circulation system of the present invention includes a plurality of cooling fluid supply connectors 166 (shown here as three connectors), e.g., cooling fluid inlet connector 158 ( FIG. 4 ), each connected to an applicator cooling fluid inlet. An identical plurality (here, three) of cooling fluid return connectors 168 are provided, each adapted to connect to a cooling fluid outlet, e.g., cooling fluid outlet connector 160 ( FIG. 4 ). Each of the plurality of cooling fluid supply connectors 166 includes a normally closed shut-off valve that opens when connected to an applicator cooling fluid inlet. The shut-off valve prevents fluid flow from the cooling fluid supply connector except when connected to the cooling fluid inlet. Each of the multiple cooling fluid return connectors 168 includes a one-way valve that only allows fluid flow into the cooling fluid return connector. This prevents fluid from flowing out of the system through the cooling fluid return connector 168, but allows return fluid to flow into the system through such connector when connected to the applicator cooling fluid outlet 160. The cooling fluid supply connector 166 is configured to connect to the cooling fluid inlet connector 158 but not to the cooling fluid outlet connector 160. Similarly, the cooling fluid return connector 168 is configured to connect to the cooling fluid outlet connector 160 but not to the cooling fluid inlet connector 158. In this way, a user cannot improperly connect a cooling fluid connection.

[0066] 11 , a cooling fluid pump 170 draws cooling fluid from a cooling fluid reservoir 174 through line 172 and pumps it through line 176 and line splitter 178 into line 180 to a plurality of cooling fluid supply connectors 166. Each cooling fluid return connector 168 connects to a line 182 that connects to a line combiner 184 that is connected to the cooling fluid reservoir 174 through line 186. Thus, cooling fluid is pumped from the reservoir to the plurality of cooling fluid supply connectors 166. Cooling fluid from the applicator flows from the cooling fluid return connector 168 back to the fluid reservoir 174. The fluid reservoir 174 can conveniently take the form of a standard IV bag filled with sterile saline, which provides the sterile saline as the cooling fluid.

[0067] In the illustrated cooling fluid circulation system of the present invention, when only a single applicator is used, one of the multiple cooling fluid supply connectors 166 is connected to the cooling fluid inlet 158 ​​of the single applicator, and one of the multiple cooling fluid return connectors 168 is connected to the cooling fluid outlet 160 of the single applicator. This provides for the flow of cooling fluid through the single applicator. Cooling fluid does not flow through either the cooling fluid supply connector or the cooling fluid return connector that is not connected to the applicator. When multiple applicators are used, a separate one of the multiple cooling fluid supply connectors 166 is connected to the cooling fluid inlet 158 ​​of each of the multiple applicators, and a separate one of the multiple cooling fluid return connectors 168 is connected to the cooling fluid outlet 160 of each of the multiple applicators. This provides for a cooling fluid supply connector 166 connected to each applicator cooling fluid inlet 158 ​​and a cooling fluid return connector 168 connected to each applicator cooling fluid outlet 160, thereby providing for the flow of cooling fluid through each of the multiple applicators attached to the system. Any number of applicators can be connected to the fluid supply system, up to the number of cooling fluid supply connectors (three are shown here). Cooling fluid does not flow through any cooling fluid supply connector or cooling fluid return connector that is not connected to an applicator. This makes the fluid supply system very simple and easy to use clinically. The operator simply connects the mating fittings of the antenna to the appropriate connector type on the cooling fluid circulation system. The inlets and outlets have different types of connector fittings to avoid mistakes. The operator only needs to connect the number of antennas to be used; other unused fittings remain blocked to prevent cooling fluid from leaking. The operator does not need to remove and discard any components or add components; they only need to connect the components together. This design also allows for the storage and sterilization of cooling fluid circulation systems tailored to all these applications, greatly simplifying clinical use. The IV bag forming the fluid reservoir is available already filled with sterile saline.For use in surgical and non-invasive procedures, all cooling fluid circulation systems and fluid reservoirs are provided sterile.

[0068] In many cases, it is desirable to maintain microwave current in the applicator as it is withdrawn from the treatment site within the body once treatment of the diseased tissue is complete. This is because, in some cases, diseased tissue from the treatment site may be left behind along the insertion and withdrawal path, which can lead to the growth of additional diseased tissue. Furthermore, in many body locations, removal of the applicator leaves an open wound along the insertion path, which can bleed. The application of heat as the applicator is withdrawn provides coagulation of tissue and blood vessels, which may prevent bleeding along the insertion path while the applicator is withdrawn from the treatment site. As shown in FIG. 9 , the narrow separation distance 22 between the conductive applicator insertion tip 16 and the active insertion end of the outer conductive sleeve 18, which is the insertion end of the shunt 20, provides a zone of high microwave intensity in this distance, which can be effectively used to coagulate tissue along the insertion path when microwave power is applied as the microwave antenna is withdrawn from the treatment tissue. While methods of stepwise path ablation are known in which the applicator is withdrawn in steps, with microwave ablative heating occurring at each step, and while it is known that path ablation can be performed with continuous withdrawal of the applicator, effective continuous path ablation requires a substantially controlled, constant, and preset applicator withdrawal rate, which is difficult to obtain during applicator withdrawal.

[0069] As shown in FIG. 9 , applicators of the present invention may include depth markings 150 visible on the exterior of the elongated applicator body at regular intervals along the elongated applicator body. The purpose of these markings is to provide an indication of the applicator's penetration depth into the body, and such markings are regularly spaced, e.g., every 1 cm, along a portion of the length of the elongated applicator body that can be used to indicate penetration depth. It has been discovered that these regularly spaced depth markings along the inserted shaft can be used to guide the applicator's withdrawal speed to provide effective coagulation of the insertion path. In this process, the system includes a sound generator that can generate a regular rhythmic sound. The sound generator can be, for example, part of the controller. By coordinating the rhythmic sound with the amount of applicator withdrawal indicated by the depth markings that appear as the applicator is withdrawn, an appropriate and consistent rate of applicator withdrawal can be achieved, ensuring uniform coagulation of tissue along the insertion path. A typical desired rate of withdrawal for an applicator of the present invention is approximately 5 mm per second at a power level of 60 watts. Thus, for example, if depth markings are spaced 1 cm apart along the inserted shaft and have a rhythm that provides an audible signal, such as a beep, every second, the rhythmic sound provides withdrawal guidance at a 5 mm rate for each audible beep. This provides a 1 cm rate every 2 seconds (every two beeps), ensuring uniform coagulation of tissue during withdrawal to reduce bleeding along the insertion path. This means that the applicator is withdrawn so that a depth mark is revealed every two beeps.

[0070] In addition to regularly spaced depth markings, it has also been found advantageous to provide warning markings 152, such as red or other color markings, visible on the exterior of the elongated applicator, located a known distance toward the attachment end of the applicator from the portion of the applicator that will cause tissue ablation (the heating or ablation zone). This distance may be, for example, approximately 2-3 cm from the attachment end of the heating zone (in the applicator shown, this is approximately 5 cm from the insertion end of the applicator). As the applicator is withdrawn from the treatment tissue, these warning markings appear to indicate that the zone of pathway ablation or coagulation is approaching the external skin surface (approximately 2 or 3 cm), thereby allowing withdrawal of the applicator to be stopped at a desired location short of the skin area to avoid damaging or coagulating tissue within the skin area. A physician withdrawing the applicator to perform pathway ablation is thus alerted to the proximity of the skin surface and can either stop pathway ablation at this point or continue pathway ablation a short additional distance, either providing adequate coagulation while also protecting the skin surface, according to the physician's best judgment.

[0071] While it is generally considered important to avoid or minimize, to the greatest extent possible, adhesion of tissue, such as heated, coagulated, or cauterized tissue, to the applicator, it has been discovered that some adhesion can be advantageous for securing the position of the applicator within the treated tissue during the treatment period. In an embodiment of the present invention, the dielectric collar 22, such as that shown in FIGS. 1, 2, 9, and 10, is not coated with a material such as a Teflon coating (which otherwise covers the dielectric collar 22 to reduce tissue adhesion), but rather the dielectric material is a material such as PEEK (polyetheretherketone) to which heated tissue adheres. Although this is a relatively small area along the applicator, upon heating, the tissue adheres to this dielectric material. This has the beneficial effect of securing the applicator to the tissue throughout the ablation procedure. This adhesion occurs within approximately the first minute of the treatment period and helps provide fixed positioning of the antenna relative to the target tissue, allowing the antenna to remain in its intended position for the remainder of the treatment period, which can typically be nine minutes or more. The PEEK material has advanced high-temperature thermoplasticity and excellent chemical resistance. It has excellent mechanical properties, with high flexural strength, impact resistance, tensile strength, is substantially rigid, and bonds well to epoxy resins. When removal of the applicator is desired (the adhesion resists pulling the applicator directly straight off the treatment tissue, and such straight removal is not recommended), the applicator can be rotated, for example, by a 30-45° rotation, which easily releases the adhesive tissue and allows removal of the applicator.

[0072] A limitation found in current microwave applicators used for microwave coagulation and ablation is that the energy distribution pattern typically extends from the proximal end of the desired coagulation and ablation zone around the microwave energy-emitting portion of the applicator, back along the applicator toward the proximal end of the applicator. This undesirably extends the coagulation and ablation zone along the applicator toward the proximal end of the applicator, beyond the tissue desired to be coagulated or ablated, forming what is referred to as a tail. This results in an elliptical or teardrop-shaped energy distribution and heating pattern shape, and similarly shaped coagulation and ablation zones, although the generally desired shape of the energy distribution pattern and coagulation and ablation zones is generally more spherical. The inventors theorize that this tail or extension of the heating pattern along the proximal portion of the applicator may be due, at least in part, to tissue desiccation surrounding this proximal portion of the applicator as a result of tissue heating, and that if tissue desiccation could be reduced, the heated tail that forms would also be reduced. As tissue heats, the heat draws moisture from the tissue, causing it to dry out. As the tissue dries, its dielectric constant decreases, and heating the tissue further dries it and ultimately carbonizes it. This heating and carbonization of tissue is not a problem in the desired ablation zone, as it only ablates the tissue where ablation is desired, but it becomes problematic when it extends the ablation zone into tissue where ablation is not desired. An example of this extension of the heating zone, creating a heated tail, is shown in FIG. 12. FIG. 12 is a numerical model, generated by a COMSOL computer modeling program, of the predicted heating pattern produced by a microwave applicator represented by a cylinder 200, with the microwave radiation and desired heating zone 25 at the distal portion of the applicator 202. Region 204 represents a dielectric collar, such as collar 22 in FIGS. 1, 2, and 10, and region 206 represents the conductive insertion tip 16 in FIGS. 1, 2, and 10.The illustrated heating pattern assumes heating and desiccation to the point of charring tissue along the entire insertion length of the applicator, represented by a cylinder 210 surrounding the applicator 200. The tissue permittivity is a constant assumed for liver tissue values ​​under normal conditions of ε=46.7 and σ=0.86 S / m, and the surrounding cylinder 210 represents dry, charred tissue with charred tissue values ​​of ε=5.2 and σ=0.13 S / m. The proximal end of the applicator is at the top of Figure 12, which shows the extension of the heating zone extending toward the proximal end of the applicator, indicating the teardrop shape of the heating zone.

[0073] 13 is a numerical model, generated by a COMSOL computer modeling program, of the predicted heating pattern produced by the same microwave applicator, represented by cylinder 200, with the microwave radiation and desired heating zone 25 at the distal portion of applicator 202. This heating pattern assumes heating and desiccation to the point of charring only the tissue along the desired heating zone, represented by cylinder 212 (modeled at a length of 4 cm), at the distal portion 202 of the applicator, extending slightly beyond each end of microwave radiation zone 25. This represents a situation in which the tissue extending from the proximal end 214 of the desired heating zone 212 toward the proximal end of the applicator at the top of FIG. 13 (sometimes referred to herein as the proximal tissue) remains moist and does not dry out. Again, the tissue permittivity is a constant assumed for liver tissue values ​​under normal conditions of ε=46.7 and σ=0.86 S / m, and the surrounding cylinder 212 represents dry, charred tissue with ε=5.2 and σ=0.13 S / m for charred tissue.

[0074] A comparison of Figures 12 and 13 shows that the heating pattern in Figure 13, where the proximal tissue remains moist, is shorter, more spherical, and has much less of a tail toward the proximal end of the applicator than the heating pattern in Figure 12, where the proximal tissue is dry. In these models, isotherm 216, representing a calculated model temperature of approximately 340° Kelvin in Figure 12, is 6.6 cm compared to 6.1 cm in Figure 13, and isotherm 218, representing a calculated model temperature of approximately 328° Kelvin in Figure 12, is 8.1 cm compared to 6.8 cm in Figure 13. These figures support the inventors' theory that the elongation of the heating pattern is due, in part, to the heating and drying of the proximal tissue. Therefore, when the proximal tissue is maintained moist during treatment, the heating pattern produced is more desirable and spherical than the heating pattern produced when the tissue is not maintained moist.

[0075] 14 is a vertical cross-sectional view of the applicator of FIG. 10 , further including one or more small openings, holes, or slots 190 extending through the outer conductive sleeve 18, which allow a portion of the fluid circulating within the cooling fluid space 82 of the applicator 14 to flow through the outer conductive sleeve 18 of the applicator 14 in the region of the openings 190 and be injected into the tissue surrounding the outer conductive sleeve. The openings 190 are positioned to inject cooling fluid into the tissue in a region of the tissue beginning around the proximal end of the desired heating region 25 (from the end of the desired heating region or primary energy emission zone toward the attachment or proximal end of the applicator) and extending a distance to the attachment or proximal end of the applicator, represented by the handle in FIG. 1 . The distance along the applicator that the fluid injection extends from the proximal end of the desired heating zone 25 toward the proximal end of the applicator, and the number and configuration of the openings around the outer conductive sleeve 18, are determined to be effective to reduce or limit tissue desiccation and to reduce or limit the degree of elongation of the heating pattern to a desired degree compared to the elongation of the heating pattern produced by a particular applicator under similar operating conditions without fluid injection. This moistened tissue is referred to as the proximal tissue adjacent to the desired heating zone. The purpose of injecting a portion of the cooling fluid circulating within the applicator into the tissue is not to directly cool the proximal tissue adjacent to the desired heating zone with the fluid, but to moisten or wet the proximal tissue adjacent to the desired heating zone so that it does not dry out. This wetting of the proximal tissue mitigates tissue desiccation that would otherwise occur and tends to maintain the normal dielectric constant of the proximal tissue. This reduces the amount of microwave energy propagating through the proximal portion of the applicator, which reduces the amount of microwave energy that transfers from the desired heating zone to the outer conductive sleeve 18 (FIG. 14).

[0076] 15 is a vertical cross-sectional view of the applicator of FIG. 2 , including the conductive shunt 20 between the dielectric collar 22 and the outer conductive sleeve 18, and additionally including one or more small openings, holes, or slots 190 extending through the outer conductive sleeve 18, as shown in FIG. 14 , which allow a portion of the fluid circulating within the cooling fluid space 82 of the applicator 14 to flow through the outer conductive sleeve 18 of the applicator 14 and be injected into the proximal tissue adjacent the desired heating zone. The configuration of the openings extending through the outer conductive sleeve 18 is spaced a short distance from the immediate proximal end of the desired heating zone 25, but for purposes of this specification, this is still considered to be approximately the proximal end of the desired heating zone. Furthermore, typically, the fluid injected into the tissue will extend somewhat from the openings toward the immediate proximal end of the desired heating zone 25. The small distance shown from just proximal to the proximal end of the desired heating zone 25 may cause the heating zone to extend a small distance toward the proximal end of the applicator, but this small distance is generally insignificant. If desired, the smaller outer diameter end 84 of the shunt 20 may be shortened so that the opening through the outer conductive sleeve 18 is positioned closer to the proximal end of the desired heating zone 25, or a pathway may be provided within the smaller outer diameter end 84 of the shunt 20 that leads to the opening through the outer conductive sleeve 18 closer to the proximal end of the desired heating zone 25.

[0077] The embodiments of Figures 14 and 15 maintain circulation of cooling fluid into and out of the applicator and through the applicator cooling fluid space 82, but the fluid flowing from the applicator through the fluid return path is less than that supplied to the applicator. A fluid circulation system such as that shown in Figure 11 may be used to supply cooling fluid to the applicator and receive the return flow of cooling fluid from the applicator. In such cases, the fluid pump 170 typically provides sufficient hydraulic pressure to propel a small amount of fluid through the opening 190 in the outer conductive sleeve 18 and into the tissue to maintain the proximal tissue adjacent the desired heating zone wet. Typical flow rates of cooling fluid within the cooling fluid space within the illustrated applicator body are in the range of 20 to 40 mL / min. The flow rate required to infuse fluid into the tissue at the proximal insertion portion of the applicator is generally less than 10 mL / min, typically in the range of 1 to 6 mL / min. 11 may generally be selected to provide sufficient flow for the number of applicators connected to the fluid circulation system to maintain cooling circulation through the applicators while still allowing a small amount of flow into the tissue. If desired or necessary, particularly if a large or varying number of applicators may be attached to the fluid circulation system, for example, more than three as is possible in the illustrated system, pressure and / or flow sensors and pump controllers may be provided to measure and maintain a pressure and / or flow rate of fluid supplied to the connected applicators that is sufficient to ensure the desired fluid infusion through the connected applicators to the proximal tissue adjacent the desired heating zone when multiple applicators are connected to the fluid circulation system, but that does not provide excessive pressure and fluid infusion when one or a few applicators are connected to the fluid circulation system.

[0078] In a further applicator embodiment, infusion of fluid from the fluid flow space within the applicator into the proximal tissue adjacent the desired heating zone can be provided by eliminating the fluid flow return path from the applicator, either by blocking the fluid return path or by eliminating the fluid return path within the applicator body, and providing a lower flow rate of cooling fluid to the applicator, for example, by providing a lower flow rate fluid pump or by providing a fluid gravity drip line typical of intravenous (IV) fluid applications. Figure 16 is a vertical cross-section similar to that of Figure 10, but without the cooling fluid outlet, without the guide sleeve 40, and additionally including one or more small openings, holes, or slots 190 extending through the outer conductive sleeve 18, as shown in Figure 14. However, in this applicator embodiment, the flow of cooling fluid into and through the cooling fluid space 82 is limited to fluid flowing through the openings 190 and into the proximal tissue adjacent the proximal end of the desired heating zone. Again, the purpose of injecting fluid into the proximal tissue adjacent to the desired heating zone is to moisten or wet the tissue adjacent to the desired heating zone and prevent it from drying out. This moistening of the proximal tissue mitigates the tissue's drying and tends to maintain the normal dielectric constant of the proximal tissue. This reduces the amount of microwave energy propagating through the proximal portion of the applicator, which in turn reduces the amount of microwave energy transmitted from the desired heating zone to the outer conductive sleeve 18 (FIG. 16). In this embodiment, cooling of the applicator by the cooling fluid flowing through the cooling fluid space 82, along the outside of the coaxial transmission line 26, and within the outer conductive sleeve 18 is much less than that provided in the embodiments of FIGS. 10 and 14 due to the much lower cooling fluid flow. As shown, typical flow rates within the applicator bodies of FIGS. 10 and 14, with their fluid inlets and outlets, are in the range of 20-40 mL / min. The flow rate required to inject fluid into the proximal tissue adjacent to the desired heating zone is less than 10 mL / min, and typically only in the range of 1-6 mL / min. Thus, only a much smaller flow of cooling fluid, in the range of less than 1-10 mL / min, flows through cooling fluid space 82.However, in many uses of the applicator, this is all that is needed during treatment.

[0079] FIG. 17 is a vertical cross-sectional view similar to that of FIG. 2 , but without the cooling fluid outlet, without the guide sleeve 40, and additionally including one or more small openings, holes, or slots 190 extending through the outer conductive sleeve 18, as shown in FIG. 15 . Again, similar to the embodiment of FIG. 16 , in this applicator embodiment, the flow of cooling fluid into and through the cooling fluid space 82 is limited to fluid flowing through the openings 190 and into the proximal tissue adjacent the proximal end of the desired heating zone 25. Similar to the embodiment of FIG. 15 , if desired, the smaller outer diameter end 84 of the shunt 20 can be shortened so that the openings through the outer conductive sleeve 18 are positioned closer to the proximal end of the desired heating zone 25, or a pathway can be provided within the smaller outer diameter end 84 of the shunt 20 that leads to the openings through the outer conductive sleeve 18 that are closer to the proximal end of the desired heating zone 25.

[0080] Because the fluid flow rate to the applicators of Figures 16 and 17 is reduced to only that required for wetting of the proximal tissue adjacent to the desired heating zone (i.e., in the range of less than 1-10 mL / min), the fluid delivery system used to supply fluid to such applicators need only provide fluid at a lower flow rate and does not require provisions for receiving return fluid from the applicator. Figure 18 is a schematic diagram illustrating a fluid delivery system similar to that of Figure 11, but without the cooling fluid return line 186 and cooling fluid return connector 168. The fluid pump 170 is typically selected to supply cooling fluid at a lower flow rate, less than about 1-10 mL / min, rather than the 20-40 mL / min provided by the pump of Figure 11. Furthermore, because control of the infused fluid may be more important in cases having only fluid infusion than in cases having fluid flow back to the fluid reservoir through cooling fluid space 82 (e.g., when a large and varying number of applicators may be attached to the fluid circulation system, more than the three possible in the illustrated system), pressure and / or flow sensors and a pump controller may be provided to measure and maintain a pressure and / or flow rate of the fluid supplied to the connected applicators that is sufficient to ensure the desired fluid infusion through the connected applicators to the proximal tissue adjacent the desired heating zone when multiple applicators are connected to the fluid circulation system, and that does not provide excessive pressure and fluid infusion when one or a few applicators are connected to the fluid circulation system. It should be noted that because the fluid supply system of FIG. 11 includes a cooling fluid return connector 168 that includes a one-way valve and is therefore shut off when the cooling fluid exhaust connector is not connected thereto, such a system of FIG. 11 operates similarly to that of FIG. 18 and can be used as a substitute for the applicators of FIG. 16 and FIG. 17, simply by adjusting the fluid output pressure and / or flow rate as needed.

[0081] FIG. 19 is a schematic diagram illustrating a fluid delivery system without a pump or a cooling fluid return line and connector. The fluid delivery system of FIG. 19 uses a fluid gravity drip line typical of intravenous (IV) fluid applications. In such cases, the fluid flow rate from the gravity drip line can be set to a predetermined flow rate, typically in the range of 1-6 mL / min, to provide a desired flow rate to each applicator attached to the fluid delivery system. This flow rate from the fluid reservoir (IV bag) is adjusted whenever the number of applicators attached to the system is changed.

[0082] In some cases, it may be desirable to provide a microwave ablation system that includes both a 915 MHz microwave generator and a 2450 MHz microwave generator with a common power source and a common control system to provide output connections for an applicator adapted to apply microwaves at a 2450 MHz frequency to the tissue to be treated and / or one or more applicators adapted to apply microwaves at a 915 MHz frequency to the tissue to be treated. The system may, for example, provide one or the other frequency selected for a particular treatment procedure, or may be adapted to provide output at both frequencies simultaneously, or may be multiplexed to provide both frequencies substantially simultaneously or timed, such that one frequency is provided for a predetermined time interval and the other frequency is subsequently provided for a predetermined time interval. Such a system may provide for the use of either 915 MHz microwaves or 2450 MHz microwaves during different treatment procedures, or may provide both 915 MHz microwaves and 2450 MHz microwaves during the same treatment procedure, under common control from a single operating system. Typically, there may be multiple tumors, some large and some small. A combined frequency system allows the patient to be prepared for the treatment of multiple tumors or even larger extended portions of a tumor using both frequencies simultaneously, with timed switching between the two frequencies, or continuously in the same patient treatment setting and system. Furthermore, the system can provide independent automatic control and treatment of different target tumor zones, automatically controlled by a common treatment controller, typically a digital computer, using a common interface to provide the operator with much easier and more practical treatment planning, setup, and delivery. Having a fully integrated system with the same power supply, computer controller, computer interface display, computer control software, and fan to provide cooling airflow to a single power supply all result in significant cost and space savings compared to having separate systems for each frequency.Additionally, the system may provide the advantages of common tissue temperature monitoring and control, maintenance of treatment data records, and faster treatment delivery resulting in reduced patient sedation time. Any applicator adapted for use at 2450 MHz may be connected to the 2450 MHz power output connector, and any applicator adapted for use at 915 MHz may be connected to the 915 MHz power output connector. The 915 MHz applicators described above are suitable for use in this system, and the following description of the dual frequency system is directed to the use of the applicators described in this invention with this 915 MHz application.

[0083] FIG. 20 is a block diagram illustrating an exemplary embodiment of a dual-frequency system of the present invention. Such a system includes a 915 MHz signal generator 300 and a 2450 MHz signal generator 302. Each of the 915 MHz signal generator and the 2450 MHz signal generator may be a separate narrow-band tunable microwave generator, which may provide a relatively high input-to-output efficiency, typically between 50% and 70%. Variable-frequency generators, such as tunable broadband generators that can be tuned over a frequency range including 915 MHz and 2450 MHz, typically operate at much lower efficiencies, typically between about 6% and possibly 20%. Therefore, a separate narrow-band tunable microwave generator provides a much higher power efficiency for the system. The low efficiency of variable-frequency microwave power generators requires much higher input power, which means that the power supply providing input power to such a variable-frequency signal generator must be more than three times larger and more expensive than a power supply providing a single narrow-band generator, and also must be rated much higher than a power supply capable of simultaneously powering two narrow-band generators. The larger the power source, the more heat is generated, which requires more airflow cooling and fan noise to remove the extra heat generated internally, and more heat is exhausted into the treatment room. The higher system efficiency provided by a more efficient narrowband tuned microwave generator allows for a smaller device package, lower cooling noise, and less heat exhausted into the treatment environment.

[0084] The system provides for simultaneous operation of both the 915 MHz signal generator and the 2450 MHz signal generator, so that, if desired, both 915 MHz and 2450 MHz microwaves can be supplied simultaneously to both the 915 MHz applicator and the 2450 MHz microwave applicator. This requires the power supply to have sufficient power output to simultaneously drive both generators at their maximum power requirements. However, with the ability to quickly switch between single generators, substantially the same results may be achieved by operating only one microwave signal generator at a time, thereby reducing the power output requirements for the power supply and the overall system. Because tissue heating is the result of average power absorption in the tissue, the applied power can be pulsed, a periodic sequence, or a continuous wave, as long as the average power is the same and the time period cannot exceed approximately 20 seconds. In such a configuration, a physician can insert both the 915 MHz and 2450 MHz applicators during an applicator positioning period and prepare the system to apply treatment through the 915 MHz antenna array and through the 2450 MHz antenna, either continuously or periodically. This can be provided by timed switching between the two signal generators, or by manually controlled switching when the physician is ready to switch to the other antenna and frequency. This can be done by moving from one treatment field to another, possibly adjacent field, with rapid switching allowing the ablation zone of the first treatment to maintain its temperature while the other is applied, or if timed switching is done during the same treatment, the entire area remains at the ablation temperature provided by time-gated switching between the two frequency modes, providing a larger, more tailored ablation pattern than what the 915 MHz phased array achieves alone. This also allows the system to time-switch its operation between the two frequency operating modes, providing simultaneous heating of smaller tumors at 2450 MHz while larger tumors are treated at 915 MHz.This switching is probably only possible by providing two separate generators to which appropriate applicators can be connected through separate connections, and if both generators are controlled by a common control system.

[0085] As noted above in the Background section, it has been found that with currently available microwave applicators, when a single 2450 MHz applicator is used to treat tissue, a small, nearly spherical heating pattern is formed in the tissue surrounding the applicator. When a single 915 MHz applicator is used, the heating pattern is larger but elliptical in shape. Furthermore, Applicant has found that when multiple applicators are used in a phased array configuration using 915 MHz, a larger, nearly spherical ablation and heating pattern can be produced than with an array of multiple antennas operating at 2450 MHz, or with single applicator ablation at either 915 MHz or 2450 MHz. Because the cancerous tumors being treated are often substantially spherical in shape, the use of 2450 MHz appears advantageous when a small, more spherical ablation pattern is desired. However, when multiple 915 MHz applicators are used in a phased array configuration, a larger, more spherical ablation pattern can be produced than with an array of multiple antennas operating at 2450 MHz, or with single applicator ablation at either 915 MHz or 2450 MHz. Therefore, to enable the provision of a wide range of ablation patterns, it has been determined that it would be advantageous to provide a microwave therapy system that can provide single applicator 2450 MHz ablation, single applicator 915 MHz ablation, and multiple applicator 915 MHz phased array ablation.

[0086] As shown in FIG. 20 , the output of the 2450 MHz signal generator 302 is connected by cable 304, e.g., a coaxial cable, to a 2450 MHz microwave output port 306, e.g., a coaxial cable connector, to which a flexible coaxial cable (not shown) is connected to connect the 2450 MHz signal generator 302 to a single 2450 MHz applicator (not shown). The output of the 915 MHz signal generator 300 can be connected directly to a 915 MHz microwave output port, to which a flexible coaxial cable is connected to connect the output of the 915 MHz signal generator 300 directly to a single 915 MHz applicator. However, this only allows the use of a single 915 MHz applicator. In many treatment situations, it has been found advantageous to provide an array of multiple 915 MHz applicators, and therefore it has been found advantageous to connect the output of the 915 MHz signal generator 300 to a 915 MHz power splitter 308. This can be done by cable 310, e.g., a coaxial cable. The 915 MHz power splitter 308 is described in detail above and is shown in FIG. 8. Such a power splitter may provide microwave power output ports 312, 314, 316, and 318. As noted above, up to three 915 MHz applicators may be connected to selected 915 MHz microwave power output ports 312, 314, 316, and 318 via coaxial cables (not shown), thereby connecting up to three 915 MHz applicators to the 915 MHz power splitter via cables and power output ports if it is desired to apply 915 MHz microwaves to tissue through a single applicator or through an arrangement of two or three applicators. One of the four 915 MHz output ports (here, output port 312) is provided as the single-connection output port 110 of FIG. 8 for use when a single 915 MHz microwave applicator is used. A single 915 MHz applicator is connected to the 915 MHz microwave power output port 312 by a flexible coaxial cable (not shown).Three of the four 915 MHz output ports (here, output ports 314, 316, and 318) correspond to the three multi-connection output ports 118 in FIG. 8 and are provided as multi-connection output ports for connecting 915 MHz applicators to either two or three of the multi-connection output ports 314, 316, and 318. The power splitter is an impedance-matched splitter circuit, as described in connection with FIG. 8, that automatically directs power to one, two, or three applicator connections while maintaining impedance matching between the 915 MHz signal generator 300 and the one, two, or three applicators connected to the 915 MHz output ports, providing efficient power transfer from the generator to the applicators. If more than four applicators are desired for the arrangement, additional power splitters can be included in the system. For example, if two power splitter circuits are used, anywhere from one to six 915 MHz applicators can be connected to the system. As described with respect to the power splitter of FIG. 8, the temperature sensor signal from a temperature sensor in an applicator connected to the power splitter can be separated from the power signal and used in the system for monitoring, control, and warning purposes.

[0087] The signal generators are controlled by a system computer controller 320, which is connected to the 2450 MHz generator 302 by an interface control and monitoring cable 322 and to the 915 MHz generator 300 by an interface control and monitoring cable 324. Signals from the computer controller 320 to each generator control the operation of the generator, for example, whether a particular generator is connected or disconnected and, if connected, the power level of the output signal generated by the generator. The generators provide signals back to the computer controller to indicate such things as the forward power level (i.e., the power level of the output signal generated by the generator) and the reflected power level (i.e., the level of any power reflected back to the generator). A control interface 326, such as a display screen and keyboard or touch screen, is connected to the computer controller, such as by cable 328, and provides information from the computer controller to a system operator, and information and instructions from the system operator to the computer controller. The computer controller is also connected to the 915 MHz power splitter 308 by an interface cable 330, allowing the computer controller to monitor the connection of the applicator to the power splitter and any sensor signals provided from the applicator to the power splitter through the microwave power line, such as signals from an applicator temperature sensor when using the above-described applicator of the present invention. If other 915 MHz applicators are used, various other signals may be provided by such applicators. Additionally, other sensors may be used in the system, such as a temperature sensor inserted into the tissue to be heated. Such a temperature sensor indicates the tissue temperature at the sensor's location, and the measured temperature may be used as a feedback control signal for the system, for example, to control the amount of power applied to the tissue, to control the temperature of the heated tissue, or to provide a warning or shut down the system if the temperature exceeds a preset maximum.If such a temperature sensor is positioned in tissue at or near the outer edge of the tissue desired to be heated, it may indicate when the normal tissue to be protected is approaching overheating and therefore the need to take protective action, such as reducing applied power or shutting down the system. If a sensor is used that provides a signal through a wire separate from the microwave power cable, such a sensor wire may be connected through connector 332 to sensor module 334, which interprets such sensor signals and provides the information to a computer controller through interface cable 336, or such signals may be connected directly to the computer controller. If one or more of the applicators used in the system are cooled, for example, by circulating a cooling fluid through the applicators, such as those described herein, the system includes a cooling system 340. The various connections between the cooling system and the applicators are not shown in FIG. 20. The system also includes a power supply 342, which provides power to each of the system components requiring power, such as the signal generator, computer controller, control interface, and cooling system, if included in the system. Power is provided to the system components by wire connections between the power supply and certain embodiments, but such connections are not shown in Figure 20. Additionally, the power supply connects to an external power source, such as a common 110 volt electrical plug.

[0088] When referring to a particular frequency, such as the 915 MHz frequency, this frequency may include frequencies within the range of frequencies approved for use. Thus, the 915 MHz frequency includes 915 MHz plus or minus 13 MHz.

[0089] While the invention is illustrated and described herein with reference to embodiments thereof presently contemplated as the best modes for carrying out the invention in actual practice, it will be understood that various modifications can be made in adapting the invention to different embodiments without departing from the broader inventive concept disclosed herein and encompassed by the following claims.

Claims

1. 1. A microwave applicator for insertion into biological tissue for heat treatment of diseased tissue within the biological tissue, the microwave applicator comprising: an elongate applicator body having an insertion end for insertion into the tissue area and an attachment end for attachment to a microwave energy source; an antenna disposed at the insertion end of the elongated applicator body for radiating microwave energy; a microwave energy transmission line disposed within the elongated applicator body for conducting microwave energy from the mounting end of the applicator to the antenna, the microwave energy transmission line having an inner conductor and an outer conductor; an outer conductive sleeve extending around and spaced from the outer conductor of the microwave energy transmission line to form an exterior of a portion of the elongated applicator body and providing a cooling fluid space between the outer conductor of the microwave energy transmission line and an inner surface of the outer conductive sleeve; a guide sleeve positioned concentrically with the microwave energy transmission line and spaced apart from the outer conductor of the microwave energy transmission line and the inner surface of the outer conductive sleeve, the guide sleeve dividing at least a portion of the cooling fluid space into an inner cooling fluid space along the outer conductor of the microwave energy transmission line and an outer cooling fluid space along the inner surface of the outer conductive sleeve, the inner cooling fluid space being spaced apart from the outer cooling fluid space a guide sleeve in communication with the cooling fluid space, whereby the guide sleeve is adapted to guide a flow of cooling fluid within the cooling fluid space to cool the microwave energy transmission line and the outer conductive sleeve; a temperature sensor positioned to measure a temperature of the cooling fluid when the cooling fluid is present in the cooling fluid space during operation of the applicator; a conductive applicator tip forming the insertion end of the applicator body and electrically coupled to the inner conductor of the transmission line; a dielectric material positioned between the conductive sleeve and the conductive applicator tip to secure the conductive sleeve away from the conductive applicator tip and to electrically insulate the conductive applicator tip from the conductive sleeve, the dielectric material having an uncoated outer surface in contact with biological tissue when heated; a microwave applicator including:

2. 2. The microwave applicator for insertion into biological tissue according to claim 1, wherein the cooling fluid space extends along the length of the microwave energy transmission line toward the insertion end and terminates just before reaching the antenna.

3. 10. The microwave applicator for insertion into living tissue of claim 1, further comprising a handle from which extend said outer conductive sleeve, said microwave energy transmission line, and said guide sleeve.

4. 4. A microwave applicator for insertion into biological tissue as described in claim 3, wherein the handle includes a cooling fluid inlet for connection to a cooling fluid source and an outlet for the flow of the cooling fluid, and when the cooling fluid is supplied through the cooling fluid inlet, the cooling fluid flows from the handle to the cooling fluid space in the elongated applicator body and from the cooling fluid space in the elongated applicator body back to the handle.

5. 5. The microwave applicator for insertion into biological tissue of claim 4, wherein when the cooling fluid is supplied from the cooling fluid inlet, the cooling fluid flows from the handle into the internal cooling fluid space, through the external cooling fluid space, and back into the handle.

6. 5. The microwave applicator for insertion into biological tissue of claim 4, wherein when the cooling fluid is supplied from the cooling fluid inlet, the cooling fluid flows from the handle to the external cooling fluid space, through the internal cooling fluid space, and back to the handle.

7. 5. The microwave applicator for insertion into biological tissue according to claim 4, wherein the guide sleeve extending from the handle along a longitudinal direction of the microwave energy transmission line terminates within the cooling fluid space towards the insertion end of the applicator before terminating in the cooling fluid space in a direction along the longitudinal direction of the microwave energy transmission line towards the insertion end of the applicator, thereby forming an undivided cooling fluid space along the longitudinal direction of the microwave energy transmission line between a termination of the guide sleeve and a termination of the cooling fluid space, and the inner cooling fluid space and the outer cooling fluid space communicate through the undivided cooling fluid space.

8. 8. The microwave applicator for insertion into biological tissue according to claim 7, wherein the temperature sensor is positioned in the handle to measure the temperature of the cooling fluid returning to the handle as the cooling fluid is supplied from the cooling fluid inlet.

9. 9. The microwave applicator for insertion into biological tissue of claim 8, wherein the temperature sensor is positioned against the outside of the outer conductive sleeve and measures the temperature of the outer conductive sleeve at the location of the temperature sensor, the temperature of the outer conductive sleeve approximating the temperature of the cooling fluid adjacent to the inner surface of the outer conductive sleeve when cooling fluid is supplied from the cooling fluid inlet.

10. 9. The microwave applicator for insertion into living tissue according to claim 8, wherein said guide sleeve is formed from a non-conductive plastic material.

11. 9. The microwave applicator for insertion into biological tissue of claim 8, further comprising a coaxial microwave energy supply cable coupled to the microwave energy transmission line in the handle for connecting the microwave energy transmission line to the microwave energy source.

12. 12. The microwave applicator for insertion into biological tissue of claim 11, wherein the coaxial microwave energy delivery cable is coupled to a microwave energy transmission line via an applicator microwave coupling circuit, the applicator microwave coupling circuit further coupling a temperature sensor to the coaxial microwave energy delivery cable, whereby a temperature sensor signal is transmitted along the coaxial microwave energy delivery cable along with the microwave energy.

13. 13. The microwave applicator for insertion into living tissue according to claim 12, wherein the temperature sensor is a thermistor and the temperature sensor signal is a DC signal.

14. a conductive shunt disposed along the length of the elongated applicator body between the outer conductive sleeve and the dielectric material, coupling the dielectric material and the conductive applicator tip to the outer conductive sleeve; 13. The microwave applicator for insertion into biological tissue of claim 12, wherein the outer conductive sleeve and the conductive shunt are connected to define a portion of the cooling fluid space toward an insertion end of the applicator, and the conductive shunt electrically couples the outer conductive sleeve to the outer conductor of the microwave energy transmission line.

15. 10. The microwave applicator for insertion into biological tissue according to claim 1, further comprising a coaxial microwave energy supply cable coupled to said microwave energy transmission line for connecting said microwave energy transmission line to said microwave energy source.

16. 16. The microwave applicator for insertion into biological tissue of claim 15, wherein the coaxial microwave energy delivery cable is coupled to the microwave energy transmission line via an applicator microwave coupling circuit, the applicator microwave coupling circuit further coupling the temperature sensor to the coaxial microwave energy delivery cable, whereby a temperature sensor signal is transmitted along the coaxial microwave energy delivery cable along with microwave energy.

17. 17. The microwave applicator for insertion into living tissue according to claim 16, wherein the temperature sensor is a thermistor and the temperature sensor signal is a DC signal.

18. 2. The microwave applicator for insertion into living tissue according to claim 1, wherein said guide sleeve is formed from a non-conductive plastic material.

19. 2. The microwave applicator for insertion into biological tissue of claim 1, further comprising a conductive shunt disposed along the length of the elongated applicator body between the outer conductive sleeve and the dielectric material and joining the dielectric material and the conductive applicator tip to the outer conductive sleeve, the connection between the outer conductive sleeve and the conductive shunt defining a portion of a cooling fluid space toward the insertion end of the applicator, and the conductive shunt electrically coupling the outer conductive sleeve to the outer conductor of the microwave energy transmission line.

Images