Vapor ablation systems and methods

Abstract

To provide a prostate treatment system capable of applying condensable vapor energy to tissue such as the prostate to shrink, damage, and denature the prostate.SOLUTION: A prostate treatment system includes an introducer shaft, a vapor generator configured to generate a condensable vapor, a vapor delivery needle in communication with the vapor generator and movably disposed within the introducer shaft, a wire configured to provide an electrical current to move the vapor delivery needle, a sensor configured to measure a characteristic of the electrical current flowing through at least a portion of the wire, and a controller configured to determine a state of the vapor delivery needle based on data from the sensor.SELECTED DRAWING: Figure 1C

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit of the filing dates of U.S. Provisional Patent Application No. 62,269,776, filed Dec. 18, 2015, and No. 62,357,742, filed Jul. 1, 2016, both of which are hereby incorporated by reference in their entirety.

[0002] [Incorporation by Reference] All documents, including patents and patent applications, referred to herein are hereby incorporated by reference in their entirety to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference.

[0003] The present invention relates to devices and related methods for the treatment of benign prostatic hyperplasia using minimally invasive techniques.

Background Art

[0004] Benign prostatic hyperplasia (BPH) is a common disease among middle - aged and elderly men, and the number of patients increases with age. By age 50, more than half of men have symptomatic BPH, and by age 70, nearly 90% of men have microscopic evidence of prostate enlargement. The severity of symptoms also increases with age, with 27% of patients in the 60 - 70 age group having moderate to severe symptoms and 37% of patients in their 70s having moderate to severe symptoms.

[0005] The prostate in early life is the size and shape of a walnut and weighs approximately 20 g before the hypertrophy resulting from BPH. Prostate enlargement appears to be a normal process. With age, the prostate gradually increases in size to twice or more its normal size. The fibromuscular tissue of the outer prostatic capsule restricts expansion after the gland reaches a certain size. Due to such restriction of expansion, the tissue within the capsule compresses and constricts the prostatic urethra, thus causing resistance to urine flow.

[0006] In the male urogenital anatomy, the prostate is located below the bladder and bladder neck. The walls of the bladder can expand and contract to cause a flow of urine through the urethra that extends from the bladder through the prostate and penis. The portion of the urethra surrounded by the prostate is called the prostatic urethra. The prostate also surrounds the ejaculatory ducts that have their opening ends within the prostatic urethra. During sexual stimulation, sperm are transported from the testes by the vas deferens to the prostate, which provides a fluid that combines with the sperm to form semen during ejaculation. On either side of the prostate, the vas deferens and seminal vesicles join to form a single duct called the ejaculatory duct. That is, each ejaculatory duct transports seminal vesicle secretions and sperm into the prostatic urethra.

[0007] The prostatic glandular structure can be classified into three zones: the peripheral zone, the transitional zone, and the central zone. The peripheral zone PZ comprises approximately 70% of the volume of the prostate in young men. This subcapsular portion on the posterior surface of the prostate surrounds the distal urethra, and 70 - 80% of cancers arise in the peripheral zone tissue. The central zone CZ surrounds the ejaculatory ducts and encloses approximately 20 - 25% of the prostate volume. The central zone is often the site of inflammatory processes. The transitional zone TZ is the site where prostatic hyperplasia grows and encloses approximately 5 - 10% of the volume of the glandular elements within the normal prostate, but can constitute up to 80% of such volume in the case of BPH. The transitional zone is composed of two outer prostatic lobes and the periurethral glandular region. There is a natural barrier around the transitional zone, namely, the prostatic urethra, the anterior fibromuscular stroma, and the fibrous plane between the transitional zone and the peripheral zone. The anterior fibromuscular stroma or fibromuscular band is mainly fibromuscular tissue.

[0008] BPH is typically diagnosed when a patient seeks medical treatment complaining of troublesome urinary difficulties. The main symptoms of BPH are an increase in the frequency of urination and urgency, and a significant decrease in the flow rate during urination. BPH can also cause urinary retention in the bladder, which can, in turn, lead to lower urinary tract infections (LUTIs). In many cases, LUTIs can, in turn, ascend into the kidneys and cause chronic pyelonephritis, ultimately leading to renal failure. BPH can also lead to sexual dysfunction associated with sleep disorders or psychological distress caused by severe urinary difficulties. That is, BPH can significantly change the quality of life as men age.

[0009] BPH is the result of an imbalance between the continuous production and natural death (apoptosis) of prostatic gland cells. Such overproduction of cells most significantly leads to an increase in prostate size in the transitional zone that crosses the prostatic urethra.

[0010] In the early stages of BPH, drug therapy can reduce some of the symptoms. For example, alpha blockers treat BPH by relaxing the smooth muscle tissue found in the prostate and bladder neck, which can enable urine to flow more easily from the bladder. Such drugs can prove effective until the glandular elements cause overwhelming cell proliferation within the prostate.

[0011] However, more advanced stages of BPH can only be treated by surgical or minimally invasive thermal ablation device intervention. Several methods have been developed using electro-surgical or mechanical extraction of tissue and thermal or cryoablation of the intra-capsular prostatic tissue. In many cases, such interventions only provide temporary relief, and these treatments often cause significant peri-operative discomfort and mortality. Summary of the Invention Problems to be Solved by the Invention

[0012] In one thermal ablation method, RF energy is delivered to prostatic tissue through an elongated RF needle that penetrates multiple locations within the median lobe of the prostate. The elongated RF needle is typically about 20 mm in length with an insulator that penetrates into the lobules. The resulting RF treatment thus excises tissue away from the prostatic urethra and does not target tissue close to or parallel to the prostatic urethra. The application of RF energy is typically applied for 1 to 3 minutes or longer, which allows for thermal diffusion of the RF energy to the periprostatic capsule that excises the tissue. Such an RF energy delivery method may not produce a permanent effect because smooth muscle tissue and alpha adrenergic receptors are not uniformly excised around the prostatic urethra or within the transition zone. As a result, the tissue within the median lobe of the prostate may grow and continue to impinge on the urethra, thus limiting the long-term effectiveness of the treatment.

Means for Solving the Problem

[0013] A introducer shaft sized and configured for transurethral access into a patient, a handle coupled to the introducer shaft, a vapor generator disposed on the handle and configured to generate condensable vapor, a vapor delivery needle slidably disposed within the introducer shaft in communication with the vapor generator, a magnet attached to the needle, and a solenoid actuator disposed around the magnet, the solenoid actuator including a push winding coupled to an RF current source and a pull winding coupled to the RF current source, the push winding configured to apply a first magnetic field to the magnet, the pull winding configured to apply a second magnetic field to the magnet, the first and second magnetic fields moving a distal tip of the vapor delivery needle between a retracted position inside the introducer shaft and an extended position at least partially outside the introducer shaft. A prostate treatment device is provided.

[0014] In one embodiment, the first magnetic field shares a polarity with the magnet. In another embodiment, the second magnetic field has a polarity opposite to the polarity of the magnet.

[0015] In some embodiments, the combination of the first and second magnetic fields eliminates lateral movement of the magnet as the vapor delivery needle moves between the retracted and extended positions.

[0016] In another embodiment, the combination of the first and second magnetic fields causes the force exerted on the magnet by the push coil and the pull coil to be approximately twice that exerted by a single coil.

[0017] In some embodiments, the solenoid actuator is configured to penetrate the distal tip of the vapor delivery needle into the prostate tissue as it moves from the retracted position toward the extended position.

[0018] In one embodiment, the vapor delivery needle is sized and configured to extend into the prostate tissue when the introducer shaft is positioned within the patient's urethra.

[0019] In some embodiments, the handle enables manual control of the solenoid actuator to move the vapor delivery needle between the retracted and extended positions.

[0020] In another embodiment, the device includes a vapor actuator configured to initiate a flow of condensable vapor through the vapor delivery needle.

[0021] In other embodiments, the magnet includes a neodymium-iron-boron magnet.

[0022] In yet another embodiment, the device includes a magnetic field sensor disposed near the solenoid actuator, the magnetic field sensor being configured to provide a voltage output proportional to the magnetic field generated by the magnet to determine the position of the vapor delivery needle. In some embodiments, vapor delivery is blocked if the voltage output of the magnetic field sensor indicates that the vapor delivery needle is not deployed.

[0023] In other embodiments, the device includes a current sensor coupled to both the push coil and the pull coil, and the current sensor is configured to detect a back electromotive force when the push coil or the pull coil is excited by a current source. In some embodiments, the back electromotive force appears as a decrease in the current flowing through the current sensor. In other embodiments, the back electromotive force indicates that the vapor delivery needle has been properly deployed into the extended position.

[0024] Provided is a method of treating prostate tissue, including the steps of transurethrally inserting the shaft of a prostate treatment device until the distal end of the shaft is proximate to the prostate tissue, activating a solenoid assembly to advance a vapor delivery needle from the shaft into the prostate tissue, and delivering condensable vapor from the vapor delivery needle into the prostate tissue.

[0025] In some embodiments, the condensable vapor provides a thermal effect within the prostate tissue.

[0026] In one embodiment, the push coil of the solenoid assembly applies a first magnetic field to a magnet attached to the vapor delivery needle to advance the vapor delivery needle.

[0027] In another embodiment, the pull coil of the solenoid assembly applies a second magnetic field to the magnet to advance the vapor delivery needle.

[0028] Provided is an induction vapor generator including a fluid source, an inner coil of a tube coupled to the fluid source, the inner coil including Inconel, an outer coil of conductive wire surrounding the inner coil of the tube, and an RF generator coupled to the outer coil and configured to apply an RF current to the outer coil to inductively heat the inner coil to generate vapor.

[0029] In some embodiments, the individual windings of the inner coil are soldered or welded to each other to ensure electrical contact between adjacent windings.

[0030] In one embodiment, the generator produces a calorie delivery efficiency higher than 75%.

[0031] In another embodiment, the inner coil includes an inner diameter ranging from 0.75 mm to 0.95 mm.

[0032] A vapor delivery device having a handle, a shaft coupled to the handle, a vapor delivery needle partially disposed within the shaft, a hook feature disposed within the shaft, and a solenoid actuator configured to move a distal tip of the vapor delivery needle between a retracted position inside the shaft and an extended position at least partially outside the shaft; a tray sized and configured to receive the vapor delivery device when the vapor delivery needle extends distally beyond the shaft, the tray including an opening that is aligned with the hook feature when the vapor delivery device is inserted into the tray; and a kit including a pin inserted into the opening of the tray and configured to engage the hook feature of the vapor delivery device to lock the vapor delivery needle in a predetermined position.

[0033] To better understand the present invention and to see how it can actually be implemented, some preferred embodiments will now be described by way of non-limiting examples only, with reference to the accompanying drawings which show corresponding features consistently throughout similar embodiments within the attached drawings, where like reference numerals refer to like elements.

Brief Description of the Drawings

[0034]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 1E

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8A

Figure 8B

Figure 8C

Figure 8D

Embodiments for Carrying Out the Invention

[0035] Generally, one way to treat BPH involves the step of invasively introducing heated vapor into the interior of the prostate, and the vapor controllably ablates the prostate tissue. This method can utilize vapor for applied heating energy between 50 calories and 300 calories per individual vapor treatment in an office-based procedure (assuming multiple treatments for each prostate median lobe). This method can cause local ablation of the prostate tissue, and more specifically, the applied heating energy from the vapor can be localized to ablate the tissue adjacent to the urethra without damaging the prostate tissue not adjacent to the urethra.

[0036] The disclosure of the present invention relates to the treatment of BPH, particularly to a treatment for ablating the transitional zone prostate tissue without ablating the central or peripheral zone prostate tissue. In one embodiment, the disclosure of the present invention relates to the treatment of the prostate using convective heating in the region adjacent to the prostatic urethra. This method of ablation treatment is configured to target smooth muscle tissue, alpha-adrenergic receptors, sympathetic nerve structures, and the vasculature parallel to the prostatic urethra between the bladder neck region and the seminal colliculus region to a depth of less than 2 cm.

[0037] The system can include a vapor delivery mechanism that delivers a vapor medium containing water vapor. The system can utilize a vapor source configured to provide vapor having a temperature of at least 60 - 140°C. In another embodiment, the system further includes a computer controller configured to deliver vapor at intervals ranging from 1 second to 30 seconds.

[0038] In some embodiments, the system further includes a source for drugs or other chemical substances or compounds to be delivered with the vapor. These agents include, but are not limited to, anesthetics, antibiotics, or toxic substances such as Botox®, or chemical substances capable of treating cancer tissue cells. The agent can also be a sealant, adhesive, paste, or instant adhesive, etc.

[0039] In one embodiment, a prostate treatment device can be provided that includes an introducer shaft sized and configured for transurethral access into a patient, a vapor generator configured to generate condensable vapor, a vapor delivery needle slidably disposed within the introducer shaft in communication with the vapor generator, and a solenoid actuator configured to generate a magnetic field on the vapor delivery needle to move the vapor delivery needle between a retracted position inside the introducer shaft and an extended position at least partially outside the introducer shaft.

[0040] FIG. 1A shows one embodiment of a vapor delivery system. The vapor delivery system 100 can have an elongate shaft 102 configured to be inserted into a patient's urethra and a handle portion 104 for gripping by a human hand. The vapor system 100 can include a vapor delivery needle 106 disposed on the shaft and configured to extend from a distal portion of the elongate shaft 102.

[0041] The handle can be an ergonomic rearwardly extending handle that allows a user to easily rotate the delivery device left and right to deliver vapor to the right and left of the prostate. The vapor delivery needle can extend substantially perpendicular or transverse to the shaft and can include one or more vapor delivery ports configured to deliver a flow of vapor medium into the prostate tissue from the needle.

[0042] The vapor delivery system 100 can further include one or more triggers, buttons, levers, or activation mechanisms configured to activate various functions of the system. As shown in FIG. 1A, the system can include an RF treatment trigger 107, a needle advancement trigger 109, a wash trigger 111, a needle retraction button 113, and an emergency needle release ring 115. The needle advancement trigger can be configured to extend / retract the vapor delivery needle, the RF treatment trigger can be configured to start / stop the flow of vapor, and the wash trigger can be configured to start a cooling and / or wash fluid such as saline.

[0043] In some embodiments, the trigger or activation mechanism can be operated to control the steam and / or cleaning at various levels or flow rates. For example, a single press or depression of one of the triggers can provide a standard cleaning stream of water, while a quick double press or depression of the trigger can provide a "turbo" cleaning stream of water where the flow rate of the cleaning is increased over the standard cleaning flow rate. This feature can be useful, for example, when a physician encounters an obstruction and requires additional cooling, or when there is a loss of visibility in the urethra and / or prostate due to the accumulation of blood or other body fluids.

[0044] The steam delivery system 100 can be connected to a steam source 10, a suction source 20, a fluid cooling or cleaning source 30, a light source 40, and / or an electronic controller 50 configured to control the generation of steam and the delivery of the steam from the steam source through the lumen of the shaft, through the steam delivery needle, and into the tissue. In some embodiments, the electronic controller can be disposed on or within the steam delivery system, and in other embodiments, the electronic controller can be disposed separately from the system.

[0045] Figure 1B shows an enlarged view of the distal portion of the shaft of a steam system 100 that includes a steam delivery needle 106 that extends beyond the shaft to expose a steam delivery port 108. The steam delivery ports 108 can be arranged in a pattern that optimizes the delivery of steam to tissue in a given application. For example, in a system designed for the treatment of BPH, the delivery ports 108 include three rows of four steam delivery ports, with the rows of ports spaced 120 degrees apart around the circumference of the needle, and one row of delivery ports facing distally from the leading edge of the needle to ensure resection of tissue adjacent to the prostatic urethra. Generally, the steam delivery ports can each have a unique diameter. In one embodiment, all of the steam delivery ports have the same diameter. The system 100 further includes a lumen sized to receive an endoscope or camera and can provide the physician with additional visualization and feedback. This endoscope or camera can provide a view of the distal end of the shaft that includes the view of the steam delivery needle when deployed.

[0046] Figure 1C is a cutaway internal view of a steam delivery system 100 showing a solenoid needle driver 110 and a steam generator 112. The solenoid needle drive 110 can be configured to advance and retract the steam delivery needle of the steam delivery system, as will be described in more detail below. The steam generator 112 is configured to generate high-quality steam for delivery through the steam delivery needle to the target tissue.

[0047] Figures 1D - 1E show the specific dimensions and angles of the handle assembly of a steam delivery system according to one particular embodiment. Earlier versions of the device incorporated a rotation mechanism that allowed a physician to hold the device vertically while treating either of the lateral lobes. The usefulness of this device was not affected by the working space between the patient's knees, but it increased the complexity of the procedure due to the multiple degrees of freedom within the system. The illustrated version of the device eliminates this mechanism to simplify the procedure (and simplify its manufacture and reduce costs). The elimination of the rotation function requires the physician to rotate the entire unit to access the lateral lobes, but it also allows for a reduction in size and provides easier operation of the device during use.

[0048] Based on available anthropometric data, a 5th percentile male in a typical lithotomy position within the stirrups has approximately 14 inches of space between his knees. During use of the vapor delivery device, the location of the device between the patient's upper legs is primarily based on the length of the device's shaft. This drove the device to a design that includes the step of positioning the device in the upper leg region, which provides an approximately 109° scoop angle of the handle between the handle and the shaft. This feature enables a comfortable angle of the wrist and easier trigger pull both during the in-rotation and supine positions. The incorporation of the scoop angle allows a slightly longer handle to accommodate physicians with larger hands, while also enabling that portion of the device to be directed away from the patient's upper leg during a 90° rotation of the unit to the left or right. It provides a handle length of approximately 5.8 inches (Figure 1D) that results in a swing diameter of approximately 11 inches (Figure 1E), provides an additional 27° extraction of the tubing set and cables to provide more clearance for the patient's upper leg, and enables the provision of a distal location of the retraction button, a symmetric design, and electrical activation. Previous versions of the device that utilized a lever on the back of the device that required more than 10 lbf to activate often resulted in an unstable device during this step. Due to its symmetry, the new design can be easily activated with either the index finger of the right or left hand with a force of approximately 1 / 2 lbf, leaving the device completely stable during its use.

[0049] Figures 2 to 5 illustrate the features and functionality of the solenoid needle driver of the vapor delivery device. Figure 2 is a schematic cross-sectional view showing the functionality of the solenoid needle driver 110. The solenoid needle driver includes a vapor delivery needle 106, a pull coil 116, a push coil 118, a magnet 120, a needle holder 122, a needle tube 124, a flexible tube 126, and a magnetic field sensor 128. In Figure 2, the solenoid needle driver is shown in its fully advanced position. The vapor delivery needle 106 can be rigidly attached to the magnet 120 through the needle holder 122. The magnet can then be moved laterally by generating a magnetic field within the push coil and pull coils 116 and 118, as will be described in more detail below. The magnetic field sensor 128 senses the strength of the magnetic field generated by the push coil and pull coils.

[0050] Figures 3A to 3C are exploded assembly views of additional features of the solenoid needle driver. Figure 3A shows a solenoid coil holder 130 that holds the push coil and pull coils of Figure 2. The magnet 120 in Figure 3B slides within the solenoid coil holder 130 of Figure 3A in response to the magnetic field generated by the coil windings. The needle holder 122 in Figure 3C attaches the vapor delivery needle to the magnet.

[0051] In one embodiment, the magnet can be made from grade N-48 neodymium-iron-boron having a residual induction of approximately Br ≈ 1.4 tesla. The magnet in Figure 3 has an inner surface shaped to fit over and snap onto the needle holder. Since the magnet is an orientation material with a high coercive force, the entire magnet is magnetized uniformly along its axis. The force applied to the needle driver is thus proportional to the volume of the magnet, and the extra magnet material forming the sides of the inner surface increases the needle driver force. The needle holder can include holes configured to receive an adhesive to rigidly attach the vapor delivery needle to the holder.

[0052] Referring to FIG. 2, the solenoid includes a push winding and a pull winding configured in a push / pull configuration with respect to the magnet and the needle holder. At the fully retracted needle position, the rear end of the magnet 120 is aligned with the rear end of the push winding 118. The front end of the magnet extends into the pull winding 116 at this fully retracted needle position. To advance the needle into the advanced needle position, current is passed in opposite directions through the push winding and the pull winding as shown in FIG. 4. The push winding sets up a magnetic field that repels the magnet of the same polarity out from the winding. Due to the repulsion, the magnet is susceptible to lateral movement that does not result in a stable equilibrium along the push coil axis, increasing the contact between the magnet and its surroundings and increasing the frictional resistance to axial advancement. The pull winding generates a magnetic field that pulls the magnet into the pull winding. The pull winding attracts the magnet to the axis of the coil, thereby removing the instability of the push winding. The combination of the push winding and the pull winding is approximately twice the force exerted by a single winding. The push / pull pair of windings also makes the retraction force the same as the advancement force by simply reversing the direction of the current to the coil pair as seen in FIG. 4.

[0053] In one embodiment, the push winding and the pull winding are each wound with approximately 400 turns of AWG #30 magnet wire, and each coil has a DC resistance of approximately 10 ohms. The current can be supplied to the solenoid coil by a 24 volt DC power source activated for approximately one-half second during advancement or retraction. Since the push winding and the pull winding are electrically connected in parallel, the resistance of the coil pair in this example is 5 ohms, and the solenoid current is approximately 24 / 5 = 4.8 amperes. Since the ON time is very short, the winding temperature does not significantly increase during activation. The needle advances / retracts through its entire range of approximately 11 mm in less than 0.020 seconds.

[0054] The axial force exerted on the magnet by the solenoid winding can be calculated from the formula for the force on a magnetic dipole exposed to a magnetic field gradient. The magnetic field and its gradient from the coil can be calculated from Biot-Savart's law. The force on the point dipole can be integrated over the magnet volume to give the net force acting on the needle driver. This calculation is plotted in Figure 5 for a magnet with an inner diameter of 10 mm, an outer diameter of 15 mm, and a length of 20 mm, and a push / pull winding with 408 turns of #30 copper wire. The full range of magnet movement is shown in the figure. In this range, the force is in the range of 2.5 to 5 pounds and reaches a peak at the midpoint of its movement range. The net force on the needle driver is this force minus the frictional force encountered along its movement. The entire curve in Figure 5 scales up and down in proportion to the solenoid current. Many force application scenarios are possible, including changes in force along the needle trajectory, with the retraction force being different from the advancement force.

[0055] The force on the magnet can be varied by the selective placement of the magnet material along its movement path. For example, a steel ring or washer can be placed at the distal end of the solenoid needle driver to provide a holding force on the magnet after the solenoid current is turned off. The emergency needle release ring shown in Figure 1A can serve the same purpose when it is made of magnetic steel. The initial force exerted by the solenoid winding during retraction needs to be strong enough to overcome the holding force of the washer.

[0056] The solenoid needle drivers of FIGS. 2-5 provide a function of accurately sensing the position of the vapor delivery needle. In one embodiment, the magnetic field sensor 128 can be disposed near the needle driver magnet, which provides a voltage output proportional to the magnetic field generated by the magnet. The magnetic field sensor can be positioned such that the magnetic field has a monotonic relationship with respect to the magnet position (e.g., adjacent to the proximal end of the magnet when in the retracted position as shown in FIG. 2). The magnetic field of the magnet is large compared to the magnetic field of the solenoid winding and other stray magnetic fields, and the position of the magnet and thus the position of the needle can be uniquely determined by the magnetic field sensor at any time before, during, and after needle deployment. Delivery of vapor to an under-deployed needle can thereby be blocked by a controller of the vapor delivery system. The magnet position versus time during needle deployment can also be monitored by the controller. A complete but slow or jerky movement of the magnet may indicate excessive friction within the system or a coupling of the magnet or needle.

[0057] In another embodiment, indication of the magnet / needle position can be provided by the back electromotive force that the magnet exerts on the solenoid winding. When the solenoid is excited by a constant current source, the back electromotive force appears as a voltage drop across the solenoid whenever the magnet moves. The current / voltage / back electromotive force can be measured with a current sensor in the solenoid or alternatively in a generator that provides power to the solenoid. When the solenoid is excited at a constant voltage such as a 24 volt DC power supply, the back electromotive force appears as a decrease in the current flowing through the solenoid circuit. FIG. 6 shows the normal solenoid current 132 (including the current decrease) when the needle driver magnet is deployed normally, and the fault solenoid current 134 (indicating a constant current) when movement of the magnet is blocked. The back current occurs only when the magnet is moving, indicating that the magnet and needle driver are fully deployed in about 10 milliseconds. The current remains ON for one computer sampling cycle or 50 milliseconds.

[0058] To isolate the back electromotive force, the current sensor output can be band-pass filtered to eliminate the DC level associated with non-deployment and to eliminate the high-speed transitions when the current goes ON and OFF. The amplitude of the filtered output results in pulses that may be interpreted as ON bits when sampled by the controller. If no reverse current pulse is measured after the solenoid power is switched ON, the magnet does not move and the operator is alerted. Yet another analysis of the reverse current waveform can provide improved diagnostics of the magnet and needle movement. For example, the duration of the reverse current indicates how long the magnet was moving, which is an indication of how far the magnet has moved. The noise or pulsations of the waveform can indicate points of increased friction along its movement.

[0059] FIG. 7 is a detailed view of the steam generator 112 of the steam delivery system of FIG. 1C. The steam generator 112 can include an inner steam coil 136 and an outer RF coil 138 of conductive wire surrounding the inner steam coil. Sterile water can be introduced into the inner steam coil, and the RF current applied to the lead 140 of the outer RF coil by the RF generator 139 can inductively heat the inner steam coil to generate steam, i.e., vapor. The inner steam coil can be connected to a source of sterile water through a plastic tube extending from the inner coil to the fluid source.

[0060] In a preferred embodiment, the windings of the steam coil can be composed of Inconel, i.e., a nickel / chromium stainless steel metal tube. For example, 18-gauge RF Inconel 625 tubing or 18-gauge thin-wall (TW) Inconel 625 is preferred. Alternatively, the RF frequency current flowing into the outer RF coil of FIG. 7 induces a circumferential current flow in the body of the inner steam coil. It is important to have good electrical contact between the windings of the inner steam coil.

[0061] In this case, the heating element can be modeled as a transformer having an N-turn outer RF coil and a one-turn inner steam coil. The current flowing into the inner coil can be about N times the current flowing into the RF coil. The induced inner coil current generates heat in the inner coil by ohmic (I 2 r) heating that converts the water flowing into the inner coil into steam. As described above, it is advantageous for the individual coil windings of the inner steam coil to be in physical contact, which can be achieved by soldering or welding the individual windings to each other to ensure good electrical contact between the windings. One significant advantage of an Inconel 625 coiled tube is that the oxide layer formed on its surface is thin enough to allow RF current to pass freely between adjacent windings of the inner steam coil without the requirement for soldering.

[0062] Another advantage of Inconel is that it is essentially a non-magnetic material. Permeability can enhance the coupling between the RF coil and the inner coil, but the magnetic properties of stainless steel tubes are not consistent from lot to lot of the tubes. Since the consistency of the calorie output by the device is very important, non-magnetic tubes are preferred for this application. Stainless steel such as 304 can be annealed to eliminate its magnetic properties. Another advantage of Inconel 625 tubes is that their electrical properties are almost independent of temperatures (room temperature to 350 °C) beyond the range affected by the induction heating of the inner coil. Stainless steels such as 304 or 316 not only have a much larger substantial change in electrical properties with temperature, but also due to the multiphase composition of these materials, temperature cycling can produce small but significant history-dependent and unpredictable changes in electrical properties.

[0063] The calorie output of the disclosed vapor delivery device of the present invention is related to the power input of the RF generator during treatment delivery through an efficiency factor. The calorie output will be consistent for each emission when the delivered power is constant, regardless of changes in component values due to the thermal cycle of the device. The calorie output is consistent by the device when the input power is the same for a given treatment and the efficiency factor is consistent by the device. Consistency between devices is achieved by the consistency of device manufacturing. Further, the consistency improves as the power coupling efficiency approaches 100% if the input power is kept constant. In other words, variations in device parameters have a reducing effect on the output as the percentage of a constant input power delivered to the output device approaches 100%.

[0064] In one embodiment, the RF generator is designed to servo the power sent to a setpoint at its output by measuring voltage and current at the output device, calculate the output power, and adjust the output voltage in real time to keep the output power equal to the set power. The percentage of the input power delivered to the steam coil as Joule heating can be calculated by analyzing the equivalent circuit of a vapor delivery system in which current is inductively coupled from the RF coil to the steam coil through a mutual inductance M.

[0065] The elements can be defined as follows:

[0066] V = rf generator voltage amplitude in volts delivered at a frequency f in MHz, I1 = rf current flowing into the delivery device in amperes, I2 = rf current flowing into the vapor delivery coil in amperes, R C and R1 are the ac resistances of the cable and rf coil respectively in ohms, L C and L1 are the inductances of the cable and rf coil respectively in μH, R2 is the circumferential ac resistance of the vapor delivery coil in ohms, L2 is the inductance of the vapor delivery coil in μH units, M is the mutual inductance between the rf coil and the vapor delivery coil in μH units, where M 2 = c√L1L2, 0 < c < 1, c is the transformer coupling coefficient between the rf and vapor coils.

[0067] The power coupling efficiency is defined as the ratio of the ohmic heat generated in the vapor delivery coil to the input power:

[0068] η = <I2 2 R2> / <i1v>, 0 < η < 1

[0069] The brackets <> represent the average over one cycle of a sine wave input at frequency “f”. The design goal is to make the power coupling efficiency η as close as possible to 1 (100%). Using standard mathematical analysis, the circuit equations for Figure 7 can be solved to obtain an expression for η in terms of the other circuit parameters.

[0070] η = xQ2 / (1 + xQ2 + Q2 2 ) where x = 2πfcL1 / (R C + R1) Q2 = 2πfL2 / R2

[0071] Here, x includes the parameters of the input circuit and the coupling coefficient, and Q2 includes solely the parameters of the secondary vapor delivery coil. The efficiency is plotted in Figure 10 as a function of Q2 for a fixed value of x. The efficiency has a peak value when Q2 = 1 for all values of x, and it can be seen that the efficiency increases with increasing x. One way to understand this fact is that when the electrical resistance of the inner coil is too high, the induction of eddy currents becomes small with little heat generation. As a result, when the electrical resistance of the inner coil is too small, the I2 2 R2 ohmic heat becomes small. The peak of the curve is expected.

[0072] In a practical design of the vapor delivery system, the heating element can include a nested solenoid coil, where the inner vapor coil is a single-turn winding. The formulas for the inductance of a solenoid coil and the mutual inductance of a nested solenoid coil can be found in the literature to complete the solution for the efficiency. These formulas require numerical integration. However, for long and thin nested coils, a closed-form solution is available. In this approximation, Q2 is as follows:

[0073] For a single-turn solenoid coil, Q2 = 2πfμ0μ2Dt / (4ρ) Here, μ0 = permeability of free space = 4π x 10 -7 Henry / meter μ2 = relative permeability of the vapor coil D = vapor coil diameter in meters t = the smaller of the vapor coil tube wall thickness in meters or the skin depth at the frequency f ρ = electrical resistance of the inner coil tube in ohm - meters

[0074] The combination of parameters including Q2 is selected, in a preferred embodiment, to enforce Q2 ≈ 1, thereby optimizing the power coupling efficiency. The relative permeability μ2 of the inner coil is equal to 1 for non - magnetic materials such as Inconel and annealed 300 - series stainless steel.

[0075] The operating frequency can be adjusted to set Q2 = 1, but typical medical RF generators have an operating frequency in the range of 400 - 500 kHz. Complexities such as the power radiated from the heating element occur at higher frequencies and the efficiency starts to drop at lower frequencies. The diameter and tube wall thickness can be adjusted within system constraints, and materials with appropriate electrical resistance can be selected to have Q2 as close to 1 as possible. In a preferred embodiment, the outer diameter of the inner coil is 9 mm, the wall thickness is 0.2 mm, the material is Inconel 625 with a resistivity of 1.32 ohm - m, and the operating frequency is 440 kHz which produces a calculated Q2 of 1.2 and a measured Q2 close to 1. The numerical evaluation of the inner coil inductance brings the calculated and measured values of Q2 closer to agreement.

[0076] The parameters regarding the input side of the heating element circuit can be selected to maximize the value of x within practical constraints. For example, in a single-layer RF coil, it is easy to increase L1 by using a large number of turns of thin wire, or by creating a multi-layer coil of wire with a larger diameter. In fact, heating power of 100 watts or higher may be necessary to provide sufficient vapor therapy. An AC current in the range of 5 - 20 amperes may be necessary to deliver sufficient power, and as a result, the wire selected for the RF coil should have a current-carrying capacity in this range. A wire that is too small in diameter for a given RF current will show a large increase in resistance and temperature over time during treatment. From the formula for x, an increase in resistance R1 decreases the value of x.

[0077] For example, in one embodiment, it has been found that a single-layer coil made of AWG #22 litz wire gave a higher calorie output than coils of the same length made from either #20 or #24 litz wire. Multi-layer coils may be somewhat practical. The coupling constant c decreases when the separation between the RF and vapor coils increases. In the example of a long solenoid coil, c is equal to the ratio of the cross-sectional areas of the inner and outer coils, and thus decreases in proportion to the square of the outer coil diameter for a constant vapor coil diameter. Another practical limit is that the impedance of the RF coil circuit increases with the RF coil inductance L1, requiring a higher voltage to generate a given current in the RF coil. High voltages have practical and regulatory limits in medical applications. Cable resistance also has practical limits as high cables made of large diameter copper wire are not acceptable in clinical practice. A functional vapor delivery system with x > 15 and an efficiency of 75% - 90% has been achieved.

[0078] The overall efficiency of the steam delivery system is less than 100% even when the power coupling efficiency approaches 100%. This is due to the heat lost through conduction, convection, and radiation from the heating element, as well as the delivery tube and needle, and the ohmic heating by the current in the RF coil that is partially conducted or radiated away from the inner coil. The thermal design of the delivery device minimizes these losses to about 8% of the heat generated in the steam coil. The overall efficiency of the steam delivery system is defined by an equation.

[0079] Calorie output from the needle x (4.186 joules / calorie) / treatment time = εPin where ε = overall power coupling efficiency Pin = constant power input from the Rezum generator

[0080] The calorie output from the steam delivery needle is easily measured by delivering steam to a known quantity of water with a calorimeter. For the delivery devices used in BPH treatment, the average measured calorie output was 208 calories. The BPH treatment time for these devices was 9 seconds. The delivery devices constructed from the applicant's laboratory obtained a 208 - calorie output with an input power of only 115 watts for an overall efficiency of ε = 84% (calculated from the above equation). The first commercially available delivery device obtained 208 calories with an input power of 132 watts for an overall efficiency of ε = 73%.

[0081] The heat loss from ohmic heating in the RF coil can be minimized by ensuring good thermal contact between the RF and the inner coil. This is obtained by minimizing the thickness of the electrical insulator between the two coils while still meeting the electrical safety requirements. Good results are found with an insulator that is a polyimide (Kapton) tube with a wall thickness of 0.1 mm. Similarly, using a thin - wall hypo - tube for the steam coil allows the heat generated in the rf coil to conduct better to the water in the inner tube. The trade - off here is the mechanical integrity of the hypo - tube and keeping Q2 close to 1.

[0082] The power coupling efficiency is defined as the ratio of the ohmic heating power delivered to the inner steam coil tube divided by the RF generator input power. Another loss of the calorie output from the device occurs due to heat lost by conduction, convection, and radiation along the steam path within the delivery tool handle and through the delivery device probe. These losses appear as condensation of the steam along the steam path. The large latent heat of evaporation is lost from the delivery device output when the steam condenses within the device. The condensed hot water can be delivered to the tissue but is delivered with a much smaller heat content than the steam.

[0083] The heat loss can be minimized by one or more of the following means:

[0084] 1) Insulation around the heating element. Air is a good and inexpensive insulator. In some embodiments, a low-mass baffle can be added to suppress convection.

[0085] 2) Metal reflectors on the inner surface of the handle. The metal reflectors can reflect the heat radiation back to the heating element. These reflectors must avoid eddy current heating in the reflectors (e.g., foils without a continuous current path). In some embodiments, the reflectors can be die-cut into squares to break up the current path.

[0086] 3) Minimize the length and thermal conductivity of the outer tube. The inner coil outlet of the tube connection to the steam delivery needle can be shortened or minimized.

[0087] 4) The gap around the steam delivery needle.

[0088] The above discussion of calorie delivery efficiency assumes a consistent and reliable flow of water to the inner coil for conversion to steam. In reality, the water line tubing is somewhat flexible and it can store a small amount of water when it is stretched under pressure at the beginning of the treatment. Since the sterile water is being pumped at a controlled rate, the stored water is subtracted from the water delivered to the inner coil, reducing the calorie output of the delivery device at the beginning of the treatment. The water stored within the tube flexibility is released at the end of the treatment, but since the RF power is OFF during this release, it does not contribute to the calorie output.

[0089] The length of time the flow is diverted within the tube flexibility depends on the product of the tube flexibility and the water line and inner coil flow resistances. The flow resistance of the inner steam coil is much larger than that of the water line since the water line is sized to conform over the outer diameter of the inner coil, and the flow resistance increases as the inverse fourth power of the tube inner diameter. A slight reduction in the inner coil inner diameter increases the time it takes for the water flow rate within the inner coil to reach its equilibrium value and can reduce the calorie output of the delivery device.

[0090] In fact, it has been found that the water flow to the inner coil and the calorie output of the delivery device are slight when the water line is made of a rigid non-flexible material such as PTFE (Teflon®). Somewhat more flexible materials such as high density polyethylene (HDPE) and low density polyethylene (LDPE) show only a slight calorie reduction, but a more flexible material such as PVC can have a significant reduction in calorie output at the beginning of the treatment unless the tube wall thickness is significantly increased to reduce its flexibility.

[0091] Increasing the inner diameter of the inner steam coil reduces the calorie dependence on water line tube flexibility. In one example, when the inner coil inner diameter increased from 0.84 mm to 0.89 mm, all calories were recovered using a thick PVC water line material. In production, the inner diameter of the inner coil tube must be closely specified to avoid accidental increases in flow resistance due to undersized inner diameters. The plug pull-out tube controls both the inner and outer diameters of the thin-walled hypo tube. In this process, the tube inner diameter is held to a tolerance of ±0.0005 or ±0.0127 mm.

[0092] The flexibility of the tube connecting the inner coil to the steam delivery needle must also be minimized to avoid condensation due to volume expansion within this tube and to prevent vibrations that suppress the outflow of steam from the output needle orifice. Silicon is a preferred material for the connecting tube as it can withstand high steam temperatures. In some embodiments, a fiberglass mesh is placed over the tube outer diameter to prevent its expansion. In another embodiment, a metal braid is co-extruded into the wall of the silicon tube to make it non-flexible. In yet another embodiment, a heating element is placed in the barrel of the delivery device to minimize the length of any tube connecting the heating element to the steam delivery needle.

[0093] Figures 8A - 8D show a shipping pin mechanism that prevents the steam needle of a steam delivery system from moving during shipment of the system. Referring to Figure 8A, a needle holder 122 is adhered to the steam delivery needle 106. The needle holder 122 further includes a hook feature 142 that is adapted to capture a shipping pin as described below.

[0094] Referring to Figure 8B, the steam delivery needle 106 further includes a needle seal 144, which is configured to seal the lumen of the shaft of the device that advances the needle. The needle seal prevents fluid and other debris from entering the lumen.

[0095] Figure 8C shows the vapor delivery system 100 packaged in the shipping package 143. As shown, the vapor delivery needle is advanced beyond the distal tip of the device, and the shipping pin 146 is placed through the opening of the package into the hook feature of the device to lock the position of the needle in place. Figure 8D shows a close-up view of the shipping pin 146, showing how the shipping pin travels downward through the shipping package 143 into the hook feature 142 of the vapor delivery system.

[0096] The shipping pin mechanism includes a pin that can be inserted through the tray retainer of the shipping package into the vapor delivery system. Inside the vapor delivery system, the pin aligns with and captures the hook feature of the needle holder so that the needle holder cannot move during shipping. Since the needle holder is coupled to the needle, this prevents the needle from retracting into the shaft of the device during shipping. This is necessary when the retraction of the needle during distribution is unacceptable due to the fact that the needle has a curved shape set at the emitter end. If the needle were to be retracted, this natural bend is thought to apply force to the needle seal and potentially deform the seal. Deformation of the needle seal can result in leakage during subsequent use and allow fluid or debris into the lumen of the vapor delivery system. Further, if the needle retracts into the lumen, the shape of the needle can change over time.

[0097] Upon opening the device package, the user must remove the tray retainer. Since the shipping pin snaps into the tray retainer, it naturally removes itself from the device during removal of the tray retainer. This is specifically designed to eliminate user interaction with the shipping pin.

[0098] While specific embodiments of the present invention have been described in detail above, it will be understood that this description is for illustrative purposes only and that the above description of the present invention is not exhaustive. Certain features of the present invention are shown in some drawings and not in others, but this is for convenience only, and any features can be combined with each other by the present invention. Some variations and alternatives will be apparent to those skilled in the art. Such alternatives and variations are intended to be included within the scope of the claims. The specific features presented in the dependent claims can, in combination, fall within the scope of the present invention. The present invention also encompasses embodiments in which the dependent claims are written in a multiple dependent claim format, referring to other independent claims instead.

Description of Reference Numerals

[0099] 100 System steam delivery system 110 Solenoid needle driver 112 Steam generator

Claims

**Claim 1** A prostate treatment system, comprising an introducer shaft, a vapor generator configured to generate condensable vapor, a vapor delivery needle in communication with the vapor generator and movably disposed within the introducer shaft, a wire configured to supply a current for moving the vapor delivery needle, a sensor configured to measure a characteristic of the current flowing through at least a portion of the wire, and a controller configured to determine a state of the vapor delivery needle based on data from the sensor. A prostate treatment system comprising the above components. **Claim 2** The system according to claim 1, wherein the sensor is a current sensor and the characteristic is a value of the current. **Claim 3** The system according to claim 2, wherein the controller is configured to determine that the vapor delivery needle is moving based on a decrease in the value of the current. **Claim 4** The system according to claim 3, wherein the vapor delivery needle is coupled to a magnet, and movement of the magnet generates a reverse current. **Claim 5** The system according to claim 3 or claim 4, wherein the duration of the decrease in the value of the current indicates the length of time the vapor delivery needle is moving. **Claim 6** The system according to claim 5, wherein the controller is configured to determine a movement distance of the vapor delivery needle based on the length of time the vapor delivery needle is moving. **Claim 7** The system according to claim 5, further comprising a filter configured to generate a pulse, and the controller is configured to interpret the pulse. **Claim 8** The system according to claim 7, wherein the filter is configured to reduce a high-speed transition characteristic when the current turns on or off. **Claim 9** The system according to any one of claims 2 to 4, wherein the controller is configured to interpret noise in the signal from the current sensor as a point of increased friction along the movement path of the vapor delivery needle. **Claim 10** The system according to any one of claims 1 to 4, wherein the wire includes a solenoid. **Claim 11** The system according to claim 10, wherein the sensor is disposed with the solenoid. **Claim 12** The system according to any one of claims 1 to 4, wherein the controller is configured to determine that the vapor delivery needle has failed to deploy based on data from the sensor.

13. A prostate treatment system comprising: an introducer shaft; a vapor generator configured to generate condensable vapor; a vapor delivery needle in communication with the vapor generator and movably disposed within the introducer shaft; a solenoid configured to move the vapor delivery needle when current flows through the solenoid; a current sensor configured to measure a value of the current flowing through the solenoid; and wherein a decrease in the value of the current indicates movement of the vapor delivery needle.

14. The system according to claim 13, wherein a duration of the decrease in the value of the current indicates a length of time the vapor delivery needle is moving.

15. The system according to claim 13, wherein the current sensor is disposed with the solenoid.

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