X-ray source that forms a three-dimensional beam

Abstract

To control at least one of a beam pattern and a direction of an X-ray beam.SOLUTION: A three dimensional beam forming an X-ray source includes an electron beam generator (EBG) to generate an electron beam. A target element is disposed at a predetermined distance from the EBG and positioned to intercept the electron beam. The target element is responsive to the electron beam to generate an X-ray. A beam former is disposed proximate to the target element and comprised of a material which interacts with X-ray radiation to form an X-ray beam. An EBG control system controls at least one of a beam pattern and a direction of the X-ray beam by selectively varying a location where the electron beam intersects the target element so as to determine an interaction of the X-ray radiation with a beam-former structure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] (Cross - reference to related applications) This application claims the benefit of U.S. Provisional Patent Application No. 62 / 479,455, filed Mar. 31, 2017, which is hereby incorporated by reference in its entirety.

[0002] The technical field of the present disclosure includes sources of X - ray electromagnetic radiation, particularly compact sources of X - ray electromagnetic radiation.

Background Art

[0003] X - rays are widely used for various purposes in the medical field, such as in radiotherapy. Conventional X - ray sources comprise a vacuum tube that includes a cathode and an anode. A very high voltage from 50 kV to 250 kV is applied between the cathode and the anode, and a relatively low voltage is applied to a filament to heat the cathode. The filament generates electrons (by thermionic emission, field emission, or similar means) and is typically formed of tungsten or some other suitable material such as molybdenum, silver, or carbon nanotubes. The high - voltage potential between the cathode and the anode causes electrons to flow at a very high speed from the cathode to the anode through the vacuum. The X - ray source further comprises a target structure that is irradiated by the high - energy electrons. The material comprising the target can vary depending on the type of X - rays desired to be produced. Tungsten and gold are used for this purpose. When the electrons decelerate in the target material of the anode, X - rays are generated.

[0004] Radiotherapy techniques can involve external radiation doses using a technique known as external beam radiation therapy (EBRT). Intraoperative radiotherapy (IORT) is also sometimes used. IORT involves applying therapeutic levels of radiation to the tumor bed while the area is exposed and accessible during resection surgery. The advantage of IORT is that it allows for precise delivery of high doses of radiation to the target area at the desired tissue depth while minimizing exposure to surrounding healthy tissue. The wavelengths of X-ray radiation most commonly used for IORT purposes correspond to a type of X-ray radiation sometimes referred to as fluorescent X-rays, characteristic X-rays, or bremsstrahlung X-rays.

[0005] Miniature X-ray sources have the potential to be effective for IORT. However, very small conventional X-ray sources, sometimes used for this purpose, have been found to have certain drawbacks. One problem is that miniature X-ray sources are very expensive. A second problem is that they have a very limited useful life. This limited useful life usually means that the X-ray source must be replaced after being used to perform IORT on a limited number of patients. This limitation increases the cost associated with IORT procedures. A third problem is that the moderately high voltages available in very small X-ray sources may not be optimal for the desired therapeutic effect. A fourth problem is that their radiographic properties may be difficult to control in the context of IORT, just as they are not well suited to conformal radiotherapy. [Overview of the project]

[0006] This document relates to a method and system for controlling an electron beam. The method includes generating an electron beam and positioning a target element in the path of the electron beam. X-ray emission is generated as a result of the interaction between the electron beam and the target element. The X-ray emission interacts with a beamformer structure positioned in close proximity to the target element to form an X-ray beam. At least one of the beam pattern and direction of the X-ray beam is controlled by selectively changing the position where the electron beam intersects the target element to determine the interaction between the X-ray emission and the beamformer structure.

[0007] The position at which the electron beam intersects the target element can be controlled by maneuvering the electron beam with an electron beam maneuvering unit. In one aspect, the maneuvered electron beam can be guided through an extension of a closed drift tube. The drift tube is maintained under vacuum pressure to minimize electron beam attenuation. After passing through the drift tube, the electron beam can interact with the target element.

[0008] In one aspect, certain operations related to X-ray beam control are facilitated by absorbing a portion of the X-ray emission with a beamformer structure. For example, the position where the electron beam intersects a target element can be varied or controlled to indirectly control the portion of the X-ray beam absorbed by the beamformer. In some scenarios disclosed herein, the beamformer may include at least one shielding wall. The shielding wall may be positioned to at least partially divide the target element into multiple target element segments or sectors. Alternatively, one or more shielding walls may be used to form multiple shielded compartments. Such shielded compartments may be positioned to at least partially restrict the range of directions in which X-ray emission is emitted when the electron beam intersects a target element sector or segment associated with the shielded compartment.

[0009] From the above, it is understood that this method may include controlling the direction and shape of the beam by controlling the electron beam to selectively intersect with the target element in one or more of the target element sectors. The beam pattern can be further controlled by selectively choosing the position in which the electron beam intersects with the target element in one particular of the target element sectors. In a further aspect, this method may include selectively controlling the amount of X-rays transmitted by the X-ray beam in one or more different directions by selectively changing at least one of the voltage of the electron beam generator (EBG) and the electron beam residence time used when the electron beam intersects with one or more target element sectors.

[0010] This document also relates to X-ray sources. An X-ray source comprises an electron beam generator (EBG) configured to produce an electron beam. A target element is positioned at a predetermined distance from the EBG and positioned to obstruct the electron beam. A drift tube is positioned between the EBG and the target element. The EBG is configured to move the electron beam through a closed extension of the drift tube, which is maintained at a vacuum pressure.

[0011] The target element is formed from an electron beam-responsive material to facilitate the generation of X-ray emission when the electron beam captures the target element. The beamformer is positioned in close proximity to the target element and is formed from a material that interacts with the X-ray emission to form the X-ray beam. The EBG control system controls at least one of the beam pattern and direction of the X-ray beam by selectively changing the position where the electron beam intersects the target element. In some scenarios disclosed herein, the EBG control system is configured to selectively change the position where the electron beam captures the target by maneuvering the electron beam with an electron beam maneuvering unit.

[0012] The beamformer includes a high-Z material configured to absorb a portion of the X-ray radiation to facilitate the formation of an X-ray beam. The EBG control system is configured to indirectly control the portion of the X-ray beam absorbed by the beamformer by selectively changing the position where the electron beam intersects the target element.

[0013] According to one aspect, the beamformer comprises at least one shielding wall. One or more shielding walls are arranged to at least partially divide a target element into multiple target element sectors or segments. Thus, one or more shielding walls can define multiple shielded compartments. Each shielded compartment is configured to at least partially restrict the range of directions in which X-ray emission can be emitted when the electron beam intersects with the target element sector associated with a particular shielded compartment.

[0014] Using the X-ray sources described herein, an EBG control system can be configured to determine the direction of the X-ray beam by controlling which of a plurality of target element sectors intersects with the electron beam. The EBG control system can be further configured to control the beam pattern by selectively controlling the position of the electron beam in one or more target element sectors where it intersects with the target elements. In a further aspect, the EBG control system can be further configured to selectively control the amount of X-rays delivered by the X-ray beam in one or more different directions defined by the target element sectors. This result is achieved by selectively changing at least one of the EBG voltage and electron beam residence time applied when the electron beam intersects with one or more target element sectors. [Brief explanation of the drawing]

[0015] This disclosure is supplemented by the following drawings, in which corresponding parts are denoted by the same reference numerals throughout the drawings. [Figure 1]FIG. 1 is a perspective view of an x-ray source having several structures partially cut away for purposes of illustration. [Figure 2] FIG. 2 is an enlarged view of a portion of FIG. 1 showing specific details of an electron beam generator. [Figure 3] FIG. 3 is an enlarged view of a portion of FIG. 2 showing specific details of an electron beam generator. [Figure 4] FIG. 4 is an enlarged perspective view of an x-ray radiation direction control target assembly (DCTA) that is useful for understanding the x-ray source of FIG. 1. [Figure 5] FIG. 5 is an end view of the DCTA in FIG. 4. [Figure 6] FIG. 6 is an enlarged view of the DCTA in FIG. 6 that is useful for understanding the formation operation of an x-ray beam. [Figure 7] FIG. 7 is a drawing that is useful for understanding the formation operation of an x-ray beam in the x-ray source of FIG. 1. [Figure 8] FIG. 8 is a cross-sectional view showing specific details of an x-ray target disclosed herein. [Figure 9] FIGS. 9, 10, and 11 are a series of drawings that are useful for understanding a first alternative x-ray DCTA structure. [Figure 10] FIGS. 9, 10, and 11 are a series of drawings that are useful for understanding a first alternative x-ray DCTA structure. [Figure 11] FIGS. 9, 10, and 11 are a series of drawings that are useful for understanding a first alternative x-ray DCTA structure. [Figure 12] FIG. 12 is a second alternative DCTA structure. [Figure 13] FIG. 13 is a third alternative DCTA structure. [Figure 14] FIG. 14 is a fourth alternative DCTA structure. [Figure 15] FIG. 15 is a fifth alternative DCTA structure. [Figure 16] FIGS. 16A-16B are a series of drawings that are useful for understanding a sixth alternative DCTA structure and an assembly process. [Figure 17]Figures 17A and 17B are a series of drawings useful for understanding a seventh alternative DCTA structure and assembly process. [Figure 18] Figure 18 is a drawing useful for understanding an eighth alternative DCTA structure. [Figure 19] Figure 19 is a drawing useful for understanding a ninth alternative DCTA structure. [Figure 20] Figure 20 is a block diagram useful for understanding the control system of the X-ray source in FIG. 1. [Figure 21] Figures 21A - 21C are a series of drawings useful for understanding how an X-ray beam can be selectively controlled. [Figure 22] Figure 22 is a drawing useful for understanding how the X-ray source described herein can be used in an IORT procedure. [Figure 23] Figure 23 is a cross-sectional view showing a cooling arrangement for the DCTA. [Figure 24] Figure 24 is a cross-sectional view along line 24 - 24 in FIG. 23. [Figure 25] Figures 25A - 25D are a series of drawings useful for understanding techniques for controlling the beam width in a DCTA as described herein. [Figure 26] Figures 26A - 26B show a sixth alternative DCTA structure and related beam steering method. [Figure 27] Figure 27 is useful for understanding how a portion of the drift tube proximal to the DCTA is formed from an X-ray transmissive material.

Best Mode for Carrying Out the Invention

[0016] It will be immediately apparent that the solutions described herein and shown in the accompanying drawings can be reorganized and designed in a wide variety of different configurations. Therefore, as shown in the drawings, the following more detailed description does not limit the scope of this disclosure, but merely represents specific implementations in various different scenarios. While the drawings depict various aspects, they are not necessarily to scale unless otherwise indicated.

[0017] The solutions disclosed herein relate to an X-ray source that can be used for treating surface tissue structures in various radiotherapy procedures, including IORT. Useful diagrams for understanding the X-ray source 100 are provided in Figures 1 to 7. The arrangement shown in Figures 1 to 7 allows for selective directional X-rays to multiple different directions near the outer edge of the beam direction control target assembly (DCTA) 106 containing the X-ray source. Furthermore, the relative X-ray intensity pattern that defines the beam shape can be controlled to facilitate different treatment plans. For example, intensity can be selected over an angular range to vary X-ray beam parameters such as beam width.

[0018] Source 100 comprises an electron beam generator (EBG) 102, a drift tube 104, a DCTA 106, a beam focusing unit 108, and a beam maneuvering unit 110. In some scenarios, a decorative cover or housing 112 can be used to enclose the EBG 102, the beam focusing unit 108, and the beam maneuvering unit 110.

[0019] The DCTA106 facilitates a compact, maneuverable X-ray energy source, particularly suitable for IORT (Integrated Optical Resonance Therapy). Therefore, the dimensions of various components can be selected accordingly. For example, the diameter d of the drift tube 104 and DCTA106 can be advantageously selected to be approximately 30 mm or less. In some scenarios, the diameter of these components can be 10 mm or less. For example, the diameter of these components can be selected in the range of approximately 10 mm to 25 mm. Of course, the drift tube and DCTA106 are not limited in this respect, and other dimensions are also possible.

[0020] Similarly, the drift tube 104 is advantageously configured to have an extension L that extends a certain distance from the EBG 102. The length of the drift tube is advantageously selected to be long enough to extend from the cover or housing 112 into the patient's tumor cavity so that the DCTA can be selectively positioned inside the part of the human body being treated. Thus, exemplary values ​​for the drift tube length L can be in the range of 10 cm to 50 cm, with the range of 18 cm to 30 cm being suitable for most applications. Of course, the dimensions disclosed herein are provided merely as some possible examples and are not intended to limit.

[0021] Since electron beam generators are well known in the art, the structure and operation of the EBG will not be described in detail. However, a brief description of various aspects of the EBG 102 is provided herein to facilitate understanding of the disclosure. The EBG 102 can include several main components, which are best understood with reference to Figures 2 and 3. These components can include a sheath 202 that surrounds the vacuum chamber 210. In some scenarios, the sheath 202 can be made of a glass, ceramic, or metallic material that provides adequate containment of air leaks. Within the vacuum chamber, a vacuum is established and maintained by an exhaust port 216 and a getter 214.

[0022] A high-voltage connector 204 is inserted into the vacuum chamber to supply a high negative voltage to the cathode 306. A suitable high voltage applied to the cathode for the purposes of X-ray generation described herein would be in the range of -50kV to -250kV. The field shaper 206 and repeller 208 are also sealed within the vacuum chamber. The purpose of each of these components is well known in the art of electron beam generators. However, a brief explanation is provided to facilitate understanding of the solution presented herein. When heated, the cathode 306 serves as a source of electrons accelerated by the high voltage potential between the cathode 306 and the anode. In Figure 2, the purpose of the anode is provided by the sheath 202 and the repeller 208, where the sheath 202 is at ground voltage and the repeller is at a small positive potential relative to ground.

[0023] The function of the repeller 208 is to repel any positively charged ions that may be generated in the drift tube 104 or DCTA 106, preventing those ions from entering areas of cathode 306 that could cause damage. The function of the field shaper 206 is to provide a smooth surface that controls the shape and magnitude of the electric field caused by the high voltage. In the scenario of Figure 3, the grid 310 imparts the desired shape to the electric field near cathode 306 and blocks electron emission from cathode 306. Cathode 306 is fixed to the legs of heaters 309a and 309b. The legs of heaters 309a and 309b are typically made from metallic materials that have both high electrical resistance and high resistance to thermal degradation, and the current flowing through the heater legs generates high temperatures that heat cathode 306. Electrical connections to the heater legs 309a and 309b are provided by connector pins 308a and 308b, which connect the heater legs 309a and 309b to the connections in the high-voltage connector 204. The insulating disk 302 is typically made of an insulating material such as glass or ceramic and provides electrical insulation between the connector pins 308a and 308b and also provides resistance to the heat generated by the heater legs 309a and 309b.

[0024] In the scenarios disclosed herein, the drift tube 104 may be made of a material such as stainless steel. In other scenarios, the drift tube may be made of silicon carbide (SiC) in part. Alternatively, the drift tube 104 may be made of a ceramic material such as alumina or aluminum nitride. If the drift tube structure is not formed of a conductive material, a conductive inner lining 114 may be provided. For example, the conductive inner lining may be made of copper, titanium alloy, or other material applied to the inner surface of the drift tube (e.g., by sputtering, vapor deposition, or other well-known means). The hollow interior portion of the drift tube opens to a vacuum chamber 210, and the interior 212 of the drift tube 104 is also maintained at a vacuum pressure. A vacuum pressure suitable for the purpose of the solutions described herein is about 10 -5 Less than Torr or especially around 10 -9 Torr to 10 -7 It could be within the range of Torr.

[0025] Electrons, including those in the electron beam, are accelerated toward the DCTA106 by the EBG102. These electrons have a large momentum when they reach the inlet opening 116 to the drift tube 104. The interior 212 of the drift tube is maintained in vacuum, and at least the inner layer 114 of the tube is maintained at ground potential. Thus, the momentum imparted to the electrons by the EBG102 continues to carry the electrons like balls down the length of the drift tube 104 toward the DCTA106 at a very high speed (e.g., approaching the speed of light). As the electrons travel along the length of the drift tube 104, it is recognized that they are no longer accelerated electrostatically.

[0026] The beam focusing unit 108 is configured to focus the electron beam vortex moving along the length of the drift tube. For example, such focusing operations may involve adjusting the beam to control the electron focus point at the tip of the DCTA. Thus, the beam focusing unit 108 can consist of a plurality of magnetic focusing coils 117, which are controlled by selectively changing the current flowing through them. The current generates a magnetic field in each of the magnetic focusing coils 117. This magnetic field penetrates substantially into the drift tube 104 in the region surrounded by the beam focusing unit 108. The presence of a penetrating magnetic field selectively focuses the electron beam in a manner well understood in the art.

[0027] The beam steering unit 110 comprises a plurality of selectively controllable magnetic steering coils 118. The steering coils 110 are arranged to selectively change the direction of movement of electrons moving within the drift tube 104. The magnetic steering coils achieve this by generating a magnetic field (when current is passed through them). The magnetic field selectively exerts a force on the electrons moving within the drift tube 104, thus changing the direction of movement of the electron beam. As a result of this deflection of the direction of movement of the electron beam, the position at which the beam collides with the target element of the DCTA 106 can be selectively controlled.

[0028] As shown in Figures 4 and 5, the DCTA 106 is positioned at the end of the drift tube 104, distal to the EBG 102. The DCTA comprises a target 402 and a beam shield 404. The target 402 comprises a disc-shaped element positioned to traverse the direction of electron beam movement. For example, the disc-shaped element can be positioned in a plane approximately perpendicular to the direction of electron beam movement. In some scenarios, the target 402 can surround the end of the drift tube 104 distal to the EBG to facilitate the maintenance of vacuum pressure within the drift tube. The target 402 can contain a variety of different materials. However, materials with a high number of atoms, such as molybdenum, gold, and tungsten, are favorably included to facilitate the generation of X-rays with relatively high efficiency when irradiated with electrons. The structure of the target 402 will be described in more detail as the discussion progresses.

[0029] As shown in Figure 4, the beam shield 404 may include a first portion 406 positioned adjacent to one main face of the target 402 and a second portion 408 positioned adjacent to the opposite main face of the target. In some scenarios, the first portion 406 may be located inside the drift tube 104 in a vacuum environment, and the second portion 408 may be located outside the drift tube. If a portion of the beam shield 404 is located outside the drift tube as shown in Figure 4, then an X-ray transparent cap member 418 may be placed on the second portion 408 of the beam shield to surround and protect the portion of the drift tube outside the DCTA. In Figure 4, the cap member is shown only by a dotted line to facilitate understanding of the DCTA structure. However, it should be understood that the cap member 418 will extend from the end of the drift tube 104 so as to surround the first portion 406 of the DCTA.

[0030] The beam shielding 404 comprises several wall elements 410, 412. The wall element 410 associated with the first portion 406 may extend from the first principal surface of the disc-shaped target facing away from the EBG 102. The wall-shaped element 412 associated with the second portion 408 may extend toward the EBG 102 from the principal surface opposite the target facing toward the EBG 102. The wall elements 410, 412 also extend radially outward from the DCTA centerline 416 toward the periphery of the disc-shaped target 402. Thus, the wall elements form several shielded compartments 420, 422. The wall elements 410, 412 can be favorably constructed from a material that substantially interacts with X-ray photons. In some scenarios, such a material may interact with X-ray photons in such a way that they cause the X-ray photons to lose a substantial portion of their energy and momentum. Thus, one type of material that interacts well for this purpose may include a material that attenuates or absorbs X-ray energy. In some scenarios, materials with high X-ray energy absorption can be advantageously selected for this purpose.

[0031] Suitable materials with high X-ray radiation absorption are well known. Examples of such materials include stainless steel, molybdenum (MO), tungsten (W), tantalum (Ta), or other high-atom-number (high-Z) materials. In this context, high-Z materials generally refer to those with at least 21 atoms. Of course, there may be some scenarios where X-ray absorption is low. In such scenarios, other materials may be more suitable. Therefore, suitable materials for shielding walls are not necessarily limited to high-atom-number materials.

[0032] In the scenario shown in Figure 4, multiple wall elements extend radially outward from the centerline 416. However, it should be understood that the beam shielding structure is not limited in this respect, and other beam shielding structures are also possible. Some of these alternative structures are described in more detail below. Each wall element may further include rounded or chamfered corners 411 to facilitate beam formation, as described below. These rounded or chamfered corners may be positioned away from the target 402 and on a portion of the wall elements that are spaced away from the centerline 416.

[0033] As shown in Figure 4, wall element 410 can be aligned with wall element 412 to form aligned pairs of partitions 420, 422 that are shielded on the opposite side of the target 402. Each such shielded partition is associated with a corresponding target segment 414, which is bounded by a pair of wall elements 410 on one side of the target 402 and a pair of wall elements 412 on the opposite side of the target.

[0034] As is known, X-ray photons are typically emitted in a direction transverse to the collision path of the electron beam with the principal surface of the target 402. The target material has a relatively thin layer of the target material such that electrons irradiating the target 402 generate X-rays in a direction extending away from both principal surfaces of the target. Each aligned pair of shielded compartments 420, 422 (formed by wall elements 410, 412) and their corresponding target segments 414 are equipped with a beamformer. The X-rays generated when high-energy electrons interact with a particular target segment 414 are restricted in their direction of movement by the wall elements defining compartments 410, 412. This concept is shown in Figure 6, illustrating that the electron beam 602 irradiates a segment of the target 402, generating transmitted and reflected X-rays in a direction generally transverse to the collision path of the electron beam. However, in Figure 6, it can be observed that the transmitted X-rays are only transmitted within a limited range of azimuth and elevation angles α, β due to the shielding effect of the beamformer. By selectively controlling which target segment 414 is irradiated with electrons and the location within the target segment 414 where the electron beam actually strikes the target segment, X-ray beams of different directions and shapes can be selectively formed and engraved as required.

[0035] Therefore, the X-ray beam direction (defined by the principal axis of the transmitted X-ray energy) and the relative X-ray intensity pattern, including the beam shape, can be selectively changed or controlled to facilitate different treatment plans. Figure 7 illustrates this concept by showing that by selectively controlling the electron beam 706, the direction of maximum intensity of the X-ray beam 700 can be aligned in a straight line with several different directions 702, 704. The precise three-dimensional shape or relative intensity pattern of the X-ray beam 700 changes according to several factors described herein. In some scenarios, by sequentially irradiating different target segments with electrons, the electron beam can be quickly maneuvered so that it intersects different target segments within a given residence time. If more than one target segment 414 is irradiated by the electron beam, multiple beam segments can be formed in selected directions defined by the associated beamformer, each having a different beam shape or pattern.

[0036] Referring to Figure 8, it can be observed that the target 402 is formed of a very thin layer of target material 802, which can be irradiated by an electron beam 804 as described herein. The target material is advantageously selected to have a relatively high number of atoms. Exemplary target materials that can be used for this purpose include molybdenum, tungsten, and gold. The thin layer of target material 802 is advantageously placed on a thicker substrate layer 806. The substrate layer is provided to facilitate a target that is more robust to the applied force and to facilitate thermal energy transfer from the metal layer. Exemplary materials that can be used for the substrate layer 806 include beryllium, aluminum, sapphire, diamond, or ceramic materials such as alumina or boron nitride. Of these, diamond is particularly advantageous for this application because it is relatively transparent to X-rays, non-toxic, strong, and provides excellent thermal conductivity.

[0037] Diamond substrate disks suitable for substrate layer 804 can be formed by chemical vapor deposition (CVD), a technique that allows for the synthesis of diamond into the shape of a spread disk or wafer. In some scenarios, these disks can have a thickness of 300–500 μm. Other thicknesses are possible, provided the substrate has sufficient strength to create a vacuum within the drift tube 104 and is not thick enough to attenuate the X-rays passing through it. In some scenarios, CVD diamond disks with a thickness of approximately 300 μm can be used for this purpose. A thin layer of target material 802, sputtered onto one side of the CVD diamond disk as described herein, can have a thickness of 2–50 μm. For example, in some scenarios, the target material can have a thickness of 10 μm. Of course, other thicknesses are possible, and the solutions presented herein are not intended to be limited by these values.

[0038] Figures 9, 10, and 11 are a series of drawings that help to understand the first alternative DCTA structure. DCTA 906 is similar to DCTA 106 but includes an additional ring element attached around the beam shield 914 to facilitate the attachment of the DCTA to the end of the drift tube 904. More specifically, the first and second parts 916, 918 of the beam shield 914 may include rings 908a, 908b, respectively. The target 914 can be positioned between the two rings. As shown in Figure 11, one or both rings can then be fixed to the end of the drift tube (for example, by brazing).

[0039] Figure 12 is useful for understanding a second alternative DCTA structure. In this scenario, the single disc-shaped X-ray target 402 shown in Figure 4 is replaced by multiple independent, smaller wedge-shaped targets 1202, each aligned with a section as shown in the same figure. In such a scenario, the wall elements 1210, 1212, corresponding to two sections 1216 and 1218 and the intermediate base plate 1220, can be fabricated from single pieces of material as needed. The sectioned wedge-shaped targets 1202 can be positioned on the intermediate base plate 1220 between the wall elements as shown, and the entire assembly can then be fixed to the end of the drift tube. In Figure 12, it can also be observed that the wall element 1210 has curved or rounded corners rather than the chamfered corners shown in Figures 4-6. Figure 13 shows a third alternative DCTA 1306 similar in configuration to that shown in Figure 12, but with multiple separate circular or disc-shaped targets 1302 instead of the wedge-shaped target 1202.

[0040] Figure 14 shows a fourth alternative DCTA structure 1406 in which the entire beam shield 1414 is located outside the drift tube. In this scenario, the target element 1402 is the end face of a hollow tubular base 1420. The wall element 1410 extends from the surface of the base plate 1408, which attaches to the drift tube distally from the EBG 102. The end face defined by the target element 1402 is spaced away from the base plate on which the wall element 1410 is located. In some scenarios, the tubular base can have a cylindrical geometry as shown; however, other tubular structures are also possible. The tubular base can advantageously have a length sufficient to position the target element 1402 at an intermediate position along the length of the DCTA. Thus, the placement of the target element can be optimally selected for the beamforming operation. Each hollow interior portion of the base is open to the vacuum defined by the interior of the drift tube 1404. As a result, the electron beam directed at a specific target element 1402 passes through the drift tube, through the interior of the pedestal 1420, through the vacuum environment, and collides with the target element 1402. Figure 15 shows a fifth alternative DCTA 1506, similar to the configuration shown in Figure 14. However, in DCTA 1506, each of the independent target elements 1402 shown in Figure 14 is replaced by multiple smaller target elements 1502.

[0041] Figures 16A and 16B are a series of diagrams useful for understanding the sixth alternative DCTA structure and assembly process. As can be understood from the discussion here, proper alignment of the first and second parts 1602 and 1604 of the beam shield 1600 is crucial to ensuring the correct function of each X-ray beamformer. This issue is complicated because the second part 1604 of the beam shield is likely not visible to the assembly technician once it is inserted into the drift tube 1614. Furthermore, it is important that the first and second parts 1602 and 1604 remain aligned after assembly.

[0042] To facilitate these alignments, it is important that the post 1606 is provided along the central axis 1620 of the second part 1604. The post 1606 can extend through the opening 1616 of the target 1612. The post may include a notch element or key structure 1608. The hole 1622 is defined within the first part 1602 along the central axis 1620. At least a portion of the hole may have a complementary notch element or key structure 1612. This complementary notch element or key structure corresponds to the geometry and shape of the notch or key structure 1608. Thus, the first and second parts 1602, 1604 can only be met in the manner shown in Figure 16B, thereby aligning the wall element 1624 of the first part 1602 with the wall element 1626 of the second part 1604.

[0043] An arrangement similar to that described in Figures 16A and 16B can be achieved instead by profiled pins in a seventh alternative DCTA structure shown in Figures 17A and 17B. As shown therein, the beam shield 1700 may include first and second parts 1702, 1704. Each of the first and second parts may include wall elements 1724, 1726 defining a plurality of guide surfaces 1722. These guide surfaces 1722 can engage a plurality of corresponding pin surfaces 1712 formed on the profiled pin 1706. When the guide surfaces and pin surfaces are properly aligned, the profiled pin can be inserted through the first and second parts along the central axis 1720. The pin head 1714 restricts the insertion of the pin into the first and second parts. Once inserted, the pin 1706 can be secured in place by a suitable fastening device. For example, the pin 1706 may have a threaded end on which a threaded nut 1708 can be positioned to hold the pin in place.

[0044] Figure 18 shows an eighth alternative DCTA 1800. The DCTA 1800 comprises a target 1802 and a beam shield 1804. The beam shield 1804 has a structure comprising a post 1820. In some scenarios, the post 1820 can be aligned with the centerline 1816 of the target 1802 and the drift tube 1814. This post can include a first portion 1806 positioned adjacent to (and extending from) one main face of the target 1802 and a second portion 1808 positioned adjacent to (and extending from) the opposite main face of the target. Thus, the first portion 1806 can be positioned inside the drift tube 104 in a vacuum environment, and the second portion 1808 can be positioned outside the drift tube as shown.

[0045] Post 1820 can be constructed as a cylindrical post as shown in the illustration. However, the acceptable configuration of the structure is not limited to this, and the post may have different cross-sectional profiles to facilitate beamforming operations. For example, the post may have a square, triangular, or rectangular cross-sectional profile. In some scenarios, an N-plane polygon (such as an N-plane regular polygon) can be selected for the cross-sectional profile. As with the wall elements of other structures described herein, post 1820 favorably includes materials that significantly attenuate X-ray energy. For example, the post may include stainless steel, molybdenum, or metals such as tungsten, tantalum, or other high-atom-number (high-Z) materials.

[0046] Figure 19 shows a ninth alternative DCTA 1900. The structure of DCTA 1900 can be similar to that of DCTA 106. Thus, the DCTA may include a beam shield 1904 comprising a first portion 1906 positioned adjacent to one main face of the target 1902, and a second portion 1908 positioned adjacent to the opposite main face of the target. In some scenarios, the first portion 1906 may be located within a part of the DCTA that is exposed to a vacuum environment in relation to the drift tube 104. The second portion 1908 may be located outside the drift tube, as shown. The beam shield 1904 comprises a plurality of wall elements 1910, 1912. The wall elements 1910 associated with the first portion 1906 may extend from a first main face of a disc-shaped target facing away from the EBG 102. The wall-shaped elements 1912 associated with the second portion 1908 may extend from the opposite main face (e.g., the target face facing the EBG 102). Wall elements 1910 and 1912 also extend radially outward from the DCTA centerline 1916 toward the periphery of the disc-shaped target 1902. Thus, the wall elements form multiple shielded compartments.

[0047] DCTA1900 is similar to many of the other DCTA structures disclosed herein. However, in Figure 19, it can be observed that the wall elements 1910 and 1912 of DCTA1900 do not extend completely to the periphery 1903 of the target element 1902. Instead, the wall elements extend only to a portion of the radial distance from the DCTA centerline 1916 to the periphery 1903 of the target element 1902. The structure shown in Figure 19 may be useful for facilitating different beam patterns compared to other DCTA structures disclosed herein.

[0048] Turning to Figure 20, an exemplary control system 2000 for controlling the X-ray source shown in Figures 1 to 7 is shown. The control system may include a control processor 2002 that controls a high-voltage source controller 2004, a high-voltage generator 2006, a coolant system 2012, a focusing coil current source 2024, a focusing current control circuit 2026, a steering coil current source 2014, and the steering current control circuit 2016. The high-voltage source controller 2004 may consist of a control circuit designed to facilitate the control of the high-voltage generator 2006. A grid control circuit 2005 and a heater control circuit 2007 may also be provided as part of the exemplary control system.

[0049] The high-voltage generator 2006 may consist of a high-voltage transformer 2008 for increasing a relatively low-voltage AC to a high voltage, and a rectifier circuit 2010 for converting the high-voltage AC to a high-voltage DC. The high-voltage DC can then be applied to the cathode and anode in the X-ray source apparatus described herein.

[0050] The coolant system 2012 may include a coolant reservoir 2013 containing a suitable fluid for cooling the DCTA 106. For example, in some scenarios water can be used for this purpose. Alternatively, oil or other types of coolants can be used to facilitate cooling. In some scenarios, a coolant can be selected that minimizes the possibility of corrosion of certain metal components, including the DCTA. A pump 2015, an electronically controlled valve 2017, and associated fluid conduits may be provided to facilitate the flow of coolant for cooling the DCTA.

[0051] In relation to one or more focusing coils 117 in Figure 1, multiple electrical connections (not shown) can be provided. These one or more focusing coils can be controlled independently using the control circuit in Figure 20. More specifically, the focusing coil current source 2024 may include a power source capable of supplying DC current to each of the one or more focusing coils 117. This current source can be connected to a focusing coil control circuit 2026 which includes an array of current control elements under the control of a control processor. Thus, the focusing current control circuit 2026 can selectively guide one or more focusing currents C1, C2, C3, ... Cn to one or more focusing coils 117 to control the focus of the electron beam. The method of focusing the electron beam is known in the art and will not be described in detail here. However, it should be understood that the magnitude of the current flowing through each of the one or more focusing coils can be selectively controlled to change the beam focus.

[0052] Similarly, multiple electrical connections (not shown) can be provided in relation to each of the one or more steering coils 118 in Figure 1. These steering coils can also be controlled independently using the control circuit in Figure 20. More specifically, the steering coil current source 2014 may include a power supply capable of supplying DC current to each of the multiple steering coils. This current source can be connected to a steering coil control circuit 2016 which includes an array of current control elements under the control of a control processor. Thus, the steering current control circuit can selectively guide steering currents I1, 12, 13, ..., In to one or more steering coils 118 in order to control the direction of the electron beam. The methods for controlling electron beam steering coils are known in the art and will not be described in detail here. For example, electron beam steering is commonly performed in conventional cathode ray tubes. Nevertheless, it should be understood that the magnitude of the current flowing through each steering coil can be selectively controlled to change the position in which the electron beam strikes the target.

[0053] It should be understood that the apparatus is not limited to the magnetic deflection of electron beams described herein. Other methods of electron beam manipulation are also possible. For example, it is well known that an applied electric field can also be used to deflect an electron beam. In such scenarios, a high-voltage deflection plate can be used to control the electron beam instead of a steering coil, and the voltage applied to the plate will change rather than the current.

[0054] The control processor 2002 may consist of one or more devices, such as a computer processor, application-specific circuitry, a field-programmable gate array (FPGA) logic device, or other circuitry programmed to perform the functions described herein. Thus, the controller may be a digital controller, an analog controller, or a controller formed from circuitry, an integrated circuit (IC), a microcontroller, or discrete components.

[0055] Figures 21A–21C are a series of diagrams useful for understanding the operation of the DCTA described herein. For convenience, the DCTA disclosed herein will be described in relation to Figures 1–8. However, it should be understood that these concepts are similarly applicable to many or all of the DCTA structures disclosed herein.

[0056] Figure 21A conceptually shows a composite X-ray beam pattern viewed along the DCTA centerline 416, which can be understood as uniformly generating X-rays in multiple radially directed beam segments 2102. Such a beam pattern can be generated when the electron beam is diffused or directed to excite all segments 414 associated with the target 402. Each radiating beam segment 2102 is generated by a corresponding beamformer, which includes a portion of the DCTA 106. In the scenario shown in Figure 21A, the beam generator is controlled (e.g., by the control system 2000) so that each beam segment absorbs substantially the same amount of X-rays for processing areas in different azimuthal directions relative to the DCTA centerline 416. Also in Figure 21A, it can be observed that the beam segments 2102 are positioned so that X-ray photons are directed at multiple different angles around the DCTA 106 in an arc of approximately 360 degrees.

[0057] The total intensity of the X-ray radiation produced by a DCTA, such as DCTA106, is approximately proportional to the square of the accelerating voltage. Therefore, in some scenarios, the intensity of the generated X-ray beam can be controlled by controlling the cathode potential relative to the anode. Independent control of the intensity and direction of each X-ray beam segment 2102 facilitates selective changes in the composite beam pattern to achieve a composite beam pattern as shown in Figure 21B. The electron beam intensity and / or residence time can be selectively varied when impacting different segments of the target to facilitate a desired radiotherapy plan. Figure 21C shows that in some scenarios, the beam intensity in a specific radial or azimuthal direction can be reduced to virtually zero. In other words, the X-ray beam in a specific radial or azimuthal direction can be essentially disabled to facilitate a specific radiotherapy plan. Control of the beam generator can be facilitated by a control system (e.g., control system 2000).

[0058] It should be noted that the beam patterns in Figures 21A to 21C are simplified two-dimensional patterns presented to facilitate a conceptual understanding of how the beam pattern can be controlled in different radial directions by varying the electron beam intensity and residence time at different locations on the target. Actual beam patterns generated using this technique are considerably more complex and will inevitably include three-dimensional radiation patterns, as schematically shown in Figure 7. Nevertheless, it is understood that electron beams generated using higher potentials will have higher X-ray beam intensity in a particular radial or azimuthal direction, and electron beams generated using lower potentials will have lower X-ray beam intensity in a particular radial or azimuthal direction. Inevitably, the total time the X-ray beam is irradiated in a particular direction affects the total amount of radiation transmitted in that direction.

[0059] The intensity of X-rays emitted by a focused electron beam strongly depends on the distance from the focal point. To control the distance of the tissue treatment volume and modify the penetration force of the X-ray beam, it may be advantageous in the case of IORT to fill the interstitial space between the X-ray source and the wound cavity with saline solution. Such an arrangement is shown in Figure 22, where the DCTA 106 can be placed within a fluid bladder 2202. The fluid bladder may be an elastic balloon-like member that inflates with a fluid 2206, such as saline solution, to fill the interstitial space 2204 between the X-ray source and the tissue wall 2208 (e.g., the tissue wall containing the tumor bed). Fluid conduits 2210, 2212 can facilitate the flow of fluid into and out of the fluid bladder. Such an arrangement can help improve the uniformity of irradiation of the tumor bed by placing the entire tissue wall at a uniform distance from the X-ray source, thus facilitating more consistent radiation exposure.

[0060] The generation of X-rays in the DCTA 106 can generate a considerable amount of heat. Therefore, in some scenarios, a separate coolant flow can be provided to the DCTA in addition to the fluid 2206 that fills the interstitial space 2204. An example of such an arrangement is shown in Figures 23 and 24. Figure 23 shows a portion of the drift tube 104 and the DCTA 106. The cooling jacket 2300 surrounding the drift tube and DCTA is shown in cross-section to show several coaxial coolers 2302, 2305. Figure 24 is a cross-sectional view of the assembly shown in Figure 23, indicated along lines 24-24. From Figures 23 and 24, it can be seen that several coaxial coolers can be configured as a sheath surrounding the DCTA (and portion of the drift tube), providing a coolant flow to carry heat away from the DCTA.

[0061] More specifically, the outer coaxial cooler tube 2302 is defined by the interstitial space between the outer sheath 2301 and the inner sheath 2304. The inner coaxial cooler tube 2305 is defined by the inner sheath and the outer surface including portions of the drift tube 104 and DCTA 106. The inner coaxial cooler tube 2305 is partially maintained by projections 2306, which maintain a gap between the inner sheath 2304 and the outer surfaces of the drift tube 104 and DCTA 106. When the X-ray source is operating, the coolant 2303 flows through the outer coaxial cooler tube 2302 toward the DCTA 106 under positive pressure.

[0062] As indicated by the arrows in Figure 23, the coolant 2303 flows to the end 2307 of the cooling jacket, where the nozzle section 2308 is located. In some scenarios, the nozzle section 2308 can be integrated with the inner sheath 2304 as shown. Alternatively, the nozzle section may comprise a separate element. The nozzle section 2308 includes multiple ports arranged to allow the coolant 2303 to flow from the outer coaxial cooling tube 2302 into the inner coaxial cooling tube 2305. The nozzle section is also used to guide a flow or spray of coolant over and around the DCTA 106 to provide a cooling effect. This flow, indicated by the arrows in Figure 23, can take the form of a continuous flow, spray, or dripping action, depending on the coolant flow pressure and the precise construction of the nozzle section. After cooling the tip of the DCTA, the coolant 2303 flows along a return path defined by the inner coaxial cooling tube 2305 in a space maintained by the projection 2306. The coolant 2303 then exits through the discharge port and out the internal coaxial cooling tube (not shown in Figure 23).

[0063] It is understood that the cooling jacket 2300 illustrated and described herein is one possible structure for facilitating the cooling of the DCTA. In this regard, it should be understood that other types of cooling sheaths are also possible and can be used without limitation. It should also be understood that there may be several scenarios in which the X-ray source can be operated at reduced voltage levels in which a cooling jacket may not be necessary.

[0064] Further control over the X-ray emission pattern can be achieved by selectively changing the location where the electron beam collides with a specific target segment 414. For example, in Figures 25A to 25D, it can be observed that the beam width of the X-ray beam generated by each beamformer can be adjusted by changing the position where the electron beam collides with a specific target segment. When the electron beam collides with the target segment closest to the centerline of the beam shielding 404, a relatively narrow beam is generated by the beamforming section. However, as the beam gradually moves radially outward from the centerline in Figures 25B to 25D, the resulting X-ray beam gradually widens in the azimuthal direction. Thus, the direction and shape of the resulting X-ray emission intensity pattern can be selectively controlled. It should be noted that the beam patterns in Figures 25A to 25D are simplified two-dimensional patterns presented to facilitate a conceptual understanding of how the beam width can be controlled by changing the position where the electron beam collides with a specific target segment. Actual beam patterns generated using this technique are considerably more complex and would inevitably include three-dimensional emission patterns similar to those shown in Figure 7.

[0065] Figures 26A and 26B illustrate a similar concept but feature beam shielding with a different structure. In Figures 26A and 26B, the beam shielding 2504 includes multiple sections 2520 that are semicircular in their profile rather than wedge-shaped. As shown in Figure 26A, selectively controlling the position where the electron beam intersects the target can help control whether the beamforming sections produce a relatively narrow X-ray beam 2502 or a relatively wide beam 2504. A wider beam is produced as the beam moves radially outward from the centerline of the beam shielding 2504.

[0066] Further effects, as shown in Figure 26A, can involve changing the position where the electron beam captures the target associated with the wall element, effectively providing a further method for maneuvering the direction of the generated X-ray beam. As the electron beam rotates near the outer edge of the compartment, the direction of the X-ray beam changes.

[0067] Referring to Figure 27, the DCTA 2700 may include a beam shield 2704 comprising a first portion 2706 positioned adjacent to one main surface of the target 2702, and a second portion 2708 positioned adjacent to the opposite main surface of the target. The first portion 2706 may be located inside the drift tube 2714 in a vacuum environment, and the second portion 2708 may be located outside the drift tube. However, in some scenarios, the main portion 2713 of the drift tube 2714 may be made of a material that absorbs or attenuates X-rays. In such examples, it may be desirable to select a material that is more transparent to X-ray radiation than the main portion 2713 of the drift tube for the end portion 2715 of the drift tube. In such scenarios, the material for the end portion 2715 may be selected to be transparent to X-rays. This arrangement allows X-rays emitted within the drift tube 2714 to escape from the interior without attenuation, thereby providing the desired therapeutic effect.

[0068] Furthermore, the DCTA disclosed herein can be configured to have a structure similar to that of the DCTA 1900 shown in Figure 19. The DCTA 1900 includes a tubular body 1920. The tubular body can support a target 1902 at a first end and a connecting ring 1922 at the opposite end. A first portion 1906 of the beam shield 1904 extends from the surface of the target so as to be positioned within the tubular body 1920. The connecting ring is configured so that the DCTA 1900 is fixed to the end of a drift tube (e.g., a drift tube 104). The connecting ring can facilitate a vacuum seal with the end of the drift tube. Thus, the inside of the tubular body 1920 can be maintained at the same vacuum pressure as the inside of the drift tube.

[0069] The tubular body 1920 can be constructed of an X-ray transparent material. As a result, the X-ray beam formed inside the tubular body is not substantially absorbed or attenuated by the structure of the tubular body 1920. An example of an X-ray transparent material that can be used for this purpose is silicon carbide (SiC). When SiC is used for this purpose, it may be advantageous to form the connecting ring 1922 from a material such as Kovar, i.e., nickel-cobalt-iron alloy. Using Kovar for this purpose makes it easier to braze the connecting ring to the body. Of course, there may be some scenarios in which it is desirable to attenuate a portion of the X-ray beam generated inside the tubular body 1920. In that case, the tubular body can instead be formed of a material that is highly absorbent of X-ray photons. An example of a material that is highly absorbent of X-ray photons is copper (Cu).

[0070] While the invention has been described and explained in relation to one or more embodiments, equivalent changes and modifications will occur to those skilled in the art by reading and understanding this specification and accompanying drawings. In addition, certain features of the invention may have been disclosed in relation to only one of several embodiments, but such features may be combined with one or more other features of other embodiments where they may be desired and advantageous for a default or particular application.

[0071] The terms used herein are intended to describe specific aspects of the systems and methods described herein and are not intended to limit disclosure. Where used herein, the singular forms “a,” “an,” and “the” are intended to also include the plural form unless the context explicitly indicates otherwise. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or their variants are used in any of the detailed description and / or claims, such terms are intended to be encompassed in a similar manner to the term “comprising.”

[0072] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as generally understood by a person of ordinary skill in the art to which this invention pertains. Unless expressly defined herein, terms as defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art, and not as idealized or overly formal.

Claims

1. The target element structure is formed of a layer of the target material, and is placed on a substrate layer provided to facilitate the transfer of thermal energy from the target material when an electron beam collides with the target element structure to generate X-rays; and The beam shield includes a main body that is positioned adjacent to the target element structure and extends away from the target element structure, The beam shielding body comprises an X-ray beamformer structure having a plurality of shielded sections, each configured to generate a narrower X-ray beam when the electron beam strikes the target element structure near the center line of the beam shielding, and to generate a wider X-ray beam as the electron beam moves radially outward from the center line of the beam shielding.

2. The X-ray beamformer structure according to claim 1, wherein the direction of the X-ray beam can be controlled by changing the position at which the electron beam intersects the target material with respect to the wall elements forming the plurality of shielded compartments.

3. The X-ray beamformer structure according to claim 1, wherein the target material comprises a metal having at least 21 atomic number.

4. The X-ray beamformer structure according to claim 1, wherein the target element structure includes the end face of the hollow tubular base.

5. The X-ray beamformer structure according to claim 4, wherein the hollow tubular base has a vacuum environment inside which the electron beam can move before it collides with the target element structure.

6. The X-ray beamformer structure according to claim 1, wherein the target element structure includes a plurality of target elements arranged in a pattern.

7. The X-ray beamformer structure according to claim 1, wherein the beam shielding includes a first portion arranged adjacent to a first main surface in the target element structure and a second portion arranged adjacent to a second main surface on the opposite side of the target element structure.

8. The X-ray beamformer structure according to claim 7, wherein, when the target element structure is coupled to a drift tube, the first portion of the beam shield is located inside the vacuum environment and the second portion of the beam shield is located outside the vacuum environment.

9. The X-ray beamformer structure according to claim 1, comprising a plurality of beamformers to which the electron beam can be directed, each of the plurality of beamformers comprising one of the plurality of shielded sections of the beam shielding and a corresponding segment of the target element structure.

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