Three-dimensional beam forming x-ray source

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 March 31, 2017, which is incorporated by reference herein in its entirety.

[0002] The technical field of this disclosure includes sources of X-ray electromagnetic radiation, and in particular compact sources of X-ray electromagnetic radiation. [Background technology]

[0003] X-rays are widely used in the medical field for various purposes, such as radiotherapy. A conventional X-ray source comprises a vacuum tube containing a cathode and an anode. A very high voltage, ranging from 50 kV to 250 kV, is applied between the cathode and the anode, and a relatively low voltage is applied to the filament to heat the cathode. The filament generates electrons (by thermionic emission, field emission, or similar means) and is usually made 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 the electrons to flow at very high velocities through the vacuum from the cathode to the anode. The X-ray source further comprises a target structure that is irradiated by the high energy electrons. The material comprising the target may vary depending on the desired type of X-rays to be produced. Tungsten and gold are used for this purpose. When the electrons are decelerated in the target material of the anode, X-rays are produced.

[0004] Radiation therapy techniques can involve the delivery of radiation doses from the outside using a technique known as external beam radiation therapy (EBRT). Intraoperative radiation therapy (IORT) is also sometimes used. IORT involves the application of therapeutic levels of radiation to the tumor bed while that area is exposed and accessible during resection surgery. The advantage of IORT is that a high dose of radiation can be delivered precisely 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. Nevertheless, the very small conventional X-ray sources sometimes used for this purpose have been found to suffer from certain drawbacks. One problem is that miniature X-ray sources are very expensive. A second problem is that they have a very limited useful operating life. This limited useful operating 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 costs associated with the IORT procedure. A third problem is that the moderately high voltages available with very small X-ray sources may not be optimal for the desired therapeutic effect. A fourth problem is that their radiation characteristics may be difficult to control in the context of IORT, such that they are not well suited for conformal radiation therapy. Summary of the Invention

[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 radiation is generated as a result of an interaction of the electron beam with the target element. The X-ray radiation interacts with a beamformer structure positioned proximate to the target element to form an X-ray beam. At least one of a beam pattern and a direction of the X-ray beam is controlled by selectively varying a location at which the electron beam intersects the target element to determine the interaction of the X-ray radiation with the beamformer structure.

[0007] The location where the electron beam intersects the target element can be controlled by steering the electron beam with an electron beam steering unit. According to one aspect, the steered electron beam can be directed through an extension of a closed drift tube. The drift tube is maintained at a vacuum pressure to minimize attenuation of the electron beam. After passing through the drift tube, the electron beam can interact with the target element.

[0008] According to one aspect, certain operations related to X-ray beam control are facilitated by absorbing a portion of the X-ray radiation in the beamformer structure. For example, the location where the electron beam intersects the 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 can include at least one shielding wall. The shielding wall can be positioned to at least partially divide the target element into multiple target element segments or sectors. Also, one or more shielding walls can be used to form multiple shielded sections. Such shielded sections can be positioned to at least partially limit the range of directions in which the X-ray radiation is emitted when the electron beam intersects the target element sector or segment associated with the shielded section.

[0009] From the foregoing, it will be appreciated that the method can include controlling the beam direction and shape by controlling the electron beam to selectively intersect the target element in one or more of the target element sectors. The beam pattern can be further controlled by selectively choosing the location at which the electron beam intersects the target element in a particular one of the target element sectors. According to a further aspect, the method can include selectively controlling the amount of x-rays delivered by the x-ray beam in one or more different directions by selectively varying at least one of an electron beam generator (EBG) voltage and an electron beam dwell time used when the electron beam intersects one or more target element sectors.

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

[0011] The target element is formed from a material responsive to the electron beam to facilitate the production of X-ray radiation when the electron beam intercepts the target element. The beamformer is disposed proximate to the target element and is formed from a material that interacts with the X-ray radiation to form the X-ray beam. The 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. In some scenarios disclosed herein, the EBG control system is configured to selectively vary a location where the electron beam intercepts the target by steering the electron beam with an electron beam steering unit.

[0012] The beamformer includes a high-Z material configured to absorb a portion of the x-ray radiation to facilitate formation of the 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 varying the location where the electron beam intersects the target element.

[0013] According to one aspect, the beamformer comprises at least one shielding wall. The one or more shielding walls are arranged to at least partially divide the target element into a plurality of target element sectors or segments. In this manner, the one or more shielding walls can define a plurality of shielded sections. Each shielded section is configured to at least partially limit a range of directions from which x-ray radiation may be emitted when the electron beam intersects a target element sector associated with a particular shielded section.

[0014] With 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 intersect with the electron beam. The EBG control system is further configured to control the beam pattern by selectively controlling the location in one or more target element sectors where the electron beam intersects with the target elements. According to a further aspect, the EBG control system is further configured to selectively control the amount of x-ray delivered by the x-ray beam in one or more different directions defined by the target element sectors. This result is achieved by selectively varying at least one of an EBG voltage and an electron beam dwell time applied when the electron beam intersects with one or more of the target element sectors. [Brief description of the drawings]

[0015] This disclosure is supplemented by the following drawings, in which like reference numbers refer to corresponding parts throughout: [Figure 1]FIG. 1 is a perspective view of an X-ray source with some structures partially cut away for better understanding. [Diagram 2] FIG. 2 is an enlarged view of a portion of FIG. 1 showing certain details of the electron beam generator. [Diagram 3] FIG. 3 is an enlarged view of a portion of FIG. 2 showing certain details of the electron beam generator. [Figure 4] FIG. 4 is an enlarged perspective view of an x-ray control target assembly (DCTA) that is useful in understanding the x-ray source of FIG. [Diagram 5] FIG. 5 is an end view of the DCTA in FIG. [Figure 6] FIG. 6 is an enlarged view of the DCTA in FIG. 6, which is useful for understanding the operation of forming the x-ray beam. [Figure 7] FIG. 7 is a diagram useful for understanding the operation of forming the x-ray beam in the x-ray source of FIG. [Figure 8] FIG. 8 is a cross-sectional view illustrating certain details of an X-Ray target disclosed herein. [Figure 9] 9, 10 and 11 are a series of drawings useful in understanding a first alternative X-ray DCTA structure. [Figure 10] 9, 10 and 11 are a series of drawings useful in understanding a first alternative X-ray DCTA structure. [Figure 11] 9, 10 and 11 are a series of drawings useful in 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] 16A-16B are a series of drawings useful in understanding a sixth alternative DCTA structure and assembly process. [Figure 17]17A and 17B are a series of drawings useful for understanding a seventh alternative DCTA structure and assembly process. [Figure 18] FIG. 18 is a diagram useful in understanding an eighth alternative DCTA structure. [Figure 19] FIG. 19 is a drawing useful for understanding a ninth alternative DCTA structure. [Figure 20] FIG. 20 is a block diagram useful for understanding the control system of the x-ray source in FIG. [Figure 21] 21A-21C are a series of drawings that are useful in understanding how an x-ray beam can be selectively controlled. [Figure 22] FIG. 22 is a diagram useful in understanding how the x-ray sources described herein can be used in an IORT procedure. [Figure 23] FIG. 23 is a cross-sectional view showing a cooling arrangement for a DCTA. [Figure 24] FIG. 24 is a cross-sectional view taken along line 24-24 in FIG. [Diagram 25] 25A-25D are a series of drawings useful for understanding techniques for controlling beamwidth in a DCTA, as described herein. [Figure 26] 26A-B show a sixth alternative DCTA structure and associated beam steering method. [Figure 27] FIG. 27 is useful in understanding how the portion of the drift tube proximal to the DCTA is formed from a radiolucent material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] It will be readily understood that the solutions described herein and illustrated in the accompanying drawings can be rearranged and designed in a wide variety of different configurations. Thus, as shown in the figures, the following more detailed description is not intended to limit the scope of the disclosure, but merely represents specific implementations in a variety of different scenarios. While various aspects are depicted in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0017] The solutions disclosed herein relate to an x-ray source that can be used to treat superficial tissue structures in a variety of radiation therapy procedures, including IORT. Drawings useful for understanding an x-ray source 100 are provided in FIGS. 1-7. The arrangement shown in FIGS. 1-7 allows x-rays to be selectively directed in a number of different directions near the outer edge of a beam direction control target assembly (DCTA) 106 that contains the x-ray source. Furthermore, the pattern of relative x-ray intensities that define the shape of the beam can be controlled to facilitate different treatment plans. For example, intensities over a range of angles can be selected to vary x-ray beam parameters such as beam width.

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

[0019] The DCTA 106 can facilitate a miniature source of steerable x-ray energy that is particularly suited for IORT. Thus, the dimensions of the various components can be selected accordingly. For example, the diameter d of the drift tube 104 and the DCTA 106 can be advantageously selected to be about 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 about 10 mm to 25 mm. Of course, the drift tube and the DCTA 106 are not limited in this respect and other dimensions are possible.

[0020] Similarly, the drift tube 104 is advantageously configured with an extension L that extends some 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 within the portion of the body undergoing treatment. Thus, exemplary values ​​for the drift tube length L can range from 10 cm to 50 cm, with a 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 be limiting.

[0021] Electron beam generators are well known in the art, and therefore 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 major components that are best understood with reference to Figures 2 and 3. These components can include an envelope 202 that encloses a vacuum chamber 210. In some scenarios, the envelope 202 can be constructed from a glass, ceramic, or metallic material that provides reasonable elimination of air leakage. Within the vacuum chamber, a vacuum is established and maintained by an exhaust 216 and a getter 214.

[0022] A high voltage connector 204 is inserted into the vacuum chamber to provide 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 -50 kV to -250 kV. The field shaper 206 and the repeller 208 are also enclosed within the vacuum chamber. The purpose of each of these components is well known in the art of electron beam generators. However, a brief description is provided to facilitate understanding of the solution presented herein. The cathode 306, upon heating, serves as a source of electrons that are accelerated by the high voltage potential between the cathode 306 and the anode. In FIG. 2, the purpose of the anode is provided by the envelope 202, and the repeller 208, with the envelope 202 at ground voltage and the repeller 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 and prevent them from entering the area of ​​the cathode 306 where they may 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 FIG. 3, the grid 310 imparts a desired shape to the electric field near the cathode 306 and blocks the emission of electrons from the cathode 306. The cathode 306 is fixed to the legs of the heaters 309a and 309b. The legs of the heaters 309a and 309b are typically made of a metallic material that has both high electrical resistance and high resistance to thermal degradation, and the current flowing through the legs of the heaters generates high temperatures that heat the 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 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 resists the heat generated by the heater legs 309a and 309b.

[0024] In the scenarios disclosed herein, the drift tube 104 may be constructed of a material such as stainless steel. In other scenarios, the drift tube may be constructed in part of silicon carbide (SiC). Alternatively, the drift tube 104 may be constructed 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 constructed of copper, titanium alloy, or other material applied (e.g., by sputtering, evaporation, or other well-known means) to the inner surface of the drift tube. The hollow interior portion of the drift tube opens into a vacuum chamber 210, and the interior 212 of the drift tube 104 is also maintained at vacuum pressure. A suitable vacuum pressure for the purposes of the solutions described herein is about 10 -5 Less than or equal to about 10 Torr -9 Torr to 10 -7 Torr.

[0025] The electrons comprising the electron beam are accelerated by the EBG 102 towards the DCTA 106. These electrons have a large momentum when they reach the entrance opening 116 to the drift tube 104. The interior 212 of the drift tube is maintained at a 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 EBG 102 continues to carry the electrons ballistically down the length of the drift tube 104 at very high velocities (e.g., approaching the speed of light) towards the DCTA 106. It will be appreciated that as the electrons travel along the length of the drift tube 104, they are no longer electrostatically accelerated.

[0026] The beam focusing unit 108 is provided to focus the beam vortex of electrons traveling along the length of the drift tube. For example, such focusing may involve adjusting the beam to control the focal point of the electrons at the DCTA tip. Thus, the beam focusing unit 108 may be comprised of a number of magnetic focusing coils 117 controlled by selectively varying the current passed therethrough. The passed current generates a magnetic field in each of the number of magnetic focusing coils 117. This magnetic field substantially permeates the drift tube 104 in the area enclosed by the beam focusing unit 108. The presence of the 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 result by generating a magnetic field (when energized with a current). 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 electron beam's direction of movement, the location at which the beam strikes a target element of the DCTA 106 can be selectively controlled.

[0028] As shown in FIGS. 4 and 5, the DCTA 106 is disposed at the end of the drift tube 104 that is distal from the EBG 102. The DCTA comprises a target 402 and a beam shield 404. The target 402 comprises a disk-shaped element disposed transverse to the direction of electron beam travel. For example, the disk-shaped element may be disposed in a plane that is approximately perpendicular to the direction of electron beam travel. In some scenarios, the target 402 may surround the end of the drift tube 104 distal from the EBG to facilitate maintaining a vacuum pressure within the drift tube. The target 402 may comprise a variety of different materials. However, it advantageously comprises materials such as molybdenum, gold, and tungsten that have a high atomic number to facilitate the generation of x-rays with a relatively high efficiency when irradiated with electrons. The structure of the target 402 will be described in more detail as the discussion proceeds.

[0029] As shown in FIG. 4, the beam shield 404 may include a first portion 406 disposed adjacent one major surface of the target 402 and a second portion 408 disposed adjacent an opposite major surface of the target. In some scenarios, the first portion 406 may be disposed inside the drift tube 104 in a vacuum environment, and the second portion 408 may be disposed outside the drift tube. If a portion of the beam shield 404 is disposed outside the drift tube as shown in FIG. 4, then an X-ray transparent cap member 418 may be disposed over the second portion 408 of the beam shield to enclose and protect the portion of the drift tube outside the DCTA. The cap member is shown in FIG. 4 only with dotted lines to facilitate understanding of the DCTA structure. However, it should be understood that the cap member 418 would extend from the end of the drift tube 104 to enclose the first portion 406 of the DCTA.

[0030] The beam shielding 404 comprises a number of wall elements 410, 412. The wall elements 410 associated with the first portion 406 can extend from a first major surface of the disk-shaped target facing away from the EBG 102. The wall elements 412 associated with the second portion 408 can extend toward the EBG 102 from an opposite major surface of 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 disk-shaped target 402. Thus, the wall elements form a number of shielded sections 420, 422. The wall elements 410, 412 can be advantageously constructed from a material that interacts substantially with the X-ray photons. In some scenarios, the material may interact with the X-ray photons in a manner that causes the X-ray photons to lose a substantial portion of their energy and momentum. Thus, one type of material that interacts appropriately for this purpose can include a material that attenuates or absorbs X-ray energy. In some scenarios, the material selected for this purpose may be advantageously chosen to be highly absorptive of X-ray energy.

[0031] Suitable materials that are highly absorptive of X-ray radiation are well known. For example, these materials may include certain metals such as stainless steel, molybdenum (MO), tungsten (W), tantalum (Ta), or other high atomic number (high-Z) materials. High-Z materials, as the phrase is used herein, generally include those having an atomic number of at least 21. Of course, there may be some scenarios where X-ray absorption is low. In such scenarios, other materials may be suitable. Thus, suitable materials for the shielding wall are not necessarily limited to high atomic number materials.

[0032] In the scenario shown in FIG. 4, multiple wall elements extend radially outward from a centerline 416. However, it should be understood that the beam blocking configuration is not limited in this respect and other beam blocking configurations are possible. Some such alternative configurations are described in more detail below. Each wall element may further include rounded or chamfered corners 411 to facilitate beam forming as described below. These rounded or chamfered corners may be located on portions of the wall elements that are spaced away from the centerline 416 and away from the target 402.

[0033] 4, wall elements 410 can be aligned with wall elements 412 to form an aligned pair of shielded sections 420, 422 on opposite sides of the target 402. Each such shielded section is associated with a corresponding target segment 414 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 emitted in a direction generally transverse to the collision path of the electron beam with the major surface of the target 402. The target material comprises a relatively thin layer of target material such that electrons irradiating the target 402 generate X-rays in a direction extending away from both major surfaces of the target. Each aligned pair of shielded sections 420, 422 (formed by wall elements 410, 412) and their corresponding target segments 414 comprise a beamformer. X-rays generated when energetic electrons interact with a particular target segment 414 are constrained in their direction of travel by the wall elements that define the sections 410, 412. This concept is illustrated in FIG. 6, which shows that an electron beam 602 irradiates a segment of the target 402 and generates transmitted and reflected X-rays in a direction generally transverse to the collision path of the electron beam. However, in FIG. 6, it can be observed that the shielding effect of the beamformer allows the transmitted X-rays to penetrate only at a limited range of azimuth and elevation angles α, β. By selectively controlling which target segments 414 are irradiated with electrons and the location within the target segment 414 where the electron beam actually strikes the target segment, an x-ray beam of a range of different directions and shapes can be selectively shaped and sculpted as needed.

[0035] Thus, the x-ray beam direction (defined by the principal axis of transmitted x-ray energy) and the pattern of relative x-ray intensity, including the shape of the beam, can be selectively varied or controlled to facilitate different treatment regimens. FIG. 7 illustrates this concept by showing that the direction of maximum intensity of the x-ray beam 700 can be aligned in a number of different directions 702, 704 by selectively controlling the electron beam 706. The exact three-dimensional shape or relative intensity pattern of the x-ray beam 700 varies according to several factors described herein. In some scenarios, by successively irradiating different target segments with electrons, the electron beam can be rapidly steered so that it intersects different target segments during a given dwell time. When 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] With reference to FIG. 8, it can be seen that the target 402 is formed of a very thin layer of target material 802 that can be irradiated by an electron beam 804 as described herein. The target material is advantageously selected to be a material with a relatively high atomic number. Exemplary target materials that can be used for this purpose include molybdenum, tungsten, and gold. The thin layer of target material 802 is advantageously disposed on a thicker substrate layer 806. The substrate layer is provided to facilitate a more robust target against applied forces and to facilitate thermal energy transfer from the metal layer. Exemplary materials that can be used for the substrate layer 806 can 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 the substrate layer 804 can be formed by chemical vapor deposition techniques (CVD), which allow the synthesis of diamond in the shape of a rolled out disk or wafer. In some scenarios, these disks can have a thickness of 300-500 μm. Other thicknesses are possible, provided that the substrate is strong enough to contain the vacuum in the drift tube 104 and is not so thick as to attenuate the X-rays passing through it. In some scenarios, a CVD diamond disk with a thickness of about 300 μm can be used for this purpose. The thin layer of target material 802, sputtered on one side of the CVD diamond disk as described herein, can have a thickness of 2-50 μm. For example, the target material in some scenarios 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] 9, 10, and 11 are a series of drawings useful for understanding a first alternative DCTA structure. DCTA 906 is similar to DCTA 106, but includes an additional ring element attached to the periphery of beam shield 914 to facilitate attachment of the DCTA to the end of drift tube 904. More specifically, first and second portions 916, 918 of beam shield 914 can include rings 908a, 908b, respectively. Target 914 can be positioned between the two rings. As shown in FIG. 11, one or both rings can then be secured (e.g., secured by brazing) to the end of the drift tube.

[0039] FIG. 12 is useful for understanding a second alternative DCTA structure. In this scenario, the single disk-shaped X-ray target 402 shown in FIG. 4 is replaced with multiple independent smaller wedge-shaped targets 1202, each aligned with each section as shown. In such a scenario, the wall elements 1210, 1212 corresponding to the two sections 1216 and 1218 and the intermediate base plate 1220 can be made from a single piece of material if desired. The sectioned wedge-shaped target 1202 can be placed on the intermediate base plate 1220 between the wall elements as shown, and the entire assembly can then be secured to the end of the drift tube. It can also be observed in FIG. 12 that the wall element 1210 has curved or rounded corners rather than the chamfered corners shown in FIGS. 4-6. FIG. 13 is a third alternative DCTA 1306 similar to the arrangement shown in FIG. 12, but with a plurality of separate circular or disk-shaped targets 1302 provided in place of the wedge-shaped target 1202.

[0040] FIG. 14 is a fourth alternative DCTA configuration 1406 in which the beam shield 1414 is located entirely outside the drift tube. The target element 1402 in this scenario is an end face of a hollow tubular pedestal 1420. The wall element 1410 extends from a face of a base plate 1408 that attaches to the drift tube at an end distal from the EBG 102. The end face defined by the target element 1402 is spaced apart from the base plate on which the wall element 1410 is located. In some scenarios, the tubular pedestal can have a cylindrical geometry as shown, although other tubular configurations are possible. The tubular pedestal can advantageously have a length sufficient to position the target element 1402 at an intermediate position along the length of the DCTA. In this manner, the placement of the target element can be optimally selected for beam forming operations. The hollow interior portion of each of the pedestals is open to a vacuum defined by the interior of the drift tube 1404. As a result, an electron beam aimed at a particular one of the target elements 1402 passes through the drift tube, through the interior of the pedestal 1420, through the vacuum environment, and strikes the target element 1402. Figure 15 is a fifth alternative DCTA 1506 similar to the arrangement shown in Figure 14, except that in DCTA 1506, each individual target element 1402 shown in Figure 14 is replaced with multiple smaller target elements 1502.

[0041] 16A and 16B are a series of drawings useful for understanding the sixth alternative DCTA structure and assembly process. As will be appreciated from the discussion herein, proper alignment of the first and second portions 1602, 1604 of the beam shield 1600 is important to ensure correct function of each x-ray beamformer. This issue is compounded because the second portion 1604 of the beam shield is likely not visible to the assembly technician once inserted into the drift tube 1614. Furthermore, it is important that the first and second portions 1602, 1604 remain aligned after assembly.

[0042] Importantly, to facilitate such alignment, the post 1606 is located along the central axis 1620 of the second portion 1604. The post 1606 can extend through an opening 1616 in the target 1612. The post can include a notch element or key structure 1608. A hole 1622 is defined in the first portion 1602 along the central axis 1620. At least a portion of the hole can have a complementary notch element or key structure 1612 that corresponds to the geometry and shape of the notch or key structure 1608. Thus, the first and second portions 1602, 1604 can only mate in the manner shown in FIG. 16B, whereby the wall element 1624 of the first portion 1602 is aligned with the wall element 1626 of the second portion 1604.

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

[0044] An eighth alternative DCTA 1800 is shown in FIG. The DCTA 1800 includes a target 1802 and a beam shield 1804. The beam shield 1804 has a structure including 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. The post can include a first portion 1806 disposed adjacent to (and extending from) one major surface of the target 1802 and a second portion 1808 disposed adjacent to (and extending from) an opposing major surface of the target. As such, the first portion 1806 can be disposed inside the drift tube 104 in a vacuum environment and the second portion 1808 can be disposed outside the drift tube as shown.

[0045] The post 1820 may be configured as a cylindrical post as shown. However, the permissible configuration of the structure is not limited in this respect, and the post may have different cross-sectional profiles to facilitate beam shaping operations. For example, the post may have a square, triangular, or rectangular cross-sectional profile. In some scenarios, an N-sided polygon (such as an N-sided regular polygon) may be selected for the cross-sectional profile. As with the wall elements of the other structures described herein, the post 1820 advantageously comprises a material that highly attenuates x-ray energy. For example, the post may comprise a metal such as stainless steel, molybdenum, or tungsten, tantalum, or other high atomic number (high Z) material.

[0046] FIG. 19 illustrates a ninth alternative DCTA 1900. The structure of the DCTA 1900 can be similar to that of the DCTA 106. The DCTA can thus include a beam shield 1904 comprising a first portion 1906 disposed adjacent one major surface of a target 1902 and a second portion 1908 disposed adjacent an opposite major surface of the target. In some scenarios, the first portion 1906 can be disposed within a portion of the DCTA exposed to a vacuum environment associated with the drift tube 104. The second portion 1908 can be disposed outside the drift tube as shown. The beam shield 1904 comprises a number of wall elements 1910, 1912. The wall element 1910 associated with the first portion 1906 can extend from a first major surface of the disk-shaped target facing away from the EBG 102. The wall element 1912 associated with the second portion 1908 can extend from an opposite major surface (e.g., a target surface facing toward the EBG 102). The wall elements 1910, 1912 also extend radially outward from the DCTA centerline 1916 toward the periphery of the disc-shaped target 1902. The wall elements thus form a number of shielded compartments.

[0047] The DCTA 1900 is similar to many of the other DCTA structures disclosed herein. However, in FIG. 19, it can be observed that the wall elements 1910, 1912 of the DCTA 1900 do not extend completely to the periphery 1903 of the target element 1902. Instead, the wall elements extend only a portion of the radial distance from the DCTA centerline 1916 to the periphery 1903 of the target element 1902. The structure shown in FIG. 19 may be useful for facilitating different beam patterns as compared to the other DCTA structures shown herein.

[0048] Turning to Figure 20, an exemplary control system 2000 for controlling the x-ray source shown in Figures 1-7 is shown. The control system can include a control processor 2002 that controls a high voltage supply controller 2004, a high voltage generator 2006, a coolant system 2012, a focus coil current source 2024, a focus current control circuit 2026, a steering coil current source 2014, and a steering current control circuit 2016. The high voltage supply controller 2004 can be configured with control circuitry designed to facilitate control of the high voltage generator 2006. A grid control circuit 2005 and a heater control circuit 2007 can 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 stepping up the relatively low voltage AC to a high voltage, and a rectifier circuit 2010 for converting the high voltage AC to high voltage DC. The high voltage DC may then be applied to the cathode and anode in the x-ray source devices 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 may be used for this purpose. Alternatively, oil or other types of coolants may be used to facilitate cooling. In some scenarios, a coolant may be selected that can minimize the possibility of corrosion of certain metal components that comprise the DCTA. A pump 2015, electronically controlled valve 2017, and associated fluid conduits may be provided to facilitate the flow of coolant to cool the DCTA.

[0051] A number of electrical connections (not shown) may be provided in association with one or more focusing coils 117 of FIG. 1. These one or more focusing coils may be independently controlled using the control circuit of FIG. 20. More specifically, the focusing coil current source 2024 may comprise a power supply capable of providing DC current to each of the one or more focusing coils 117. This current source may be connected to a focusing coil control circuit 2026 that includes an array of current control elements under the control of a control processor. Thus, the focusing current control circuit 2026 may selectively direct one or more focusing currents C1, C2, C3, ... Cn to the one or more focusing coils 117 to control the focus of the electron beam. Methods of focusing an electron beam are known in the art and will not be described in detail herein. However, it should be understood that the magnitude of the current passed through each of the one or more focusing coils may be selectively controlled to vary the beam focus.

[0052] Similarly, multiple electrical connections (not shown) may be provided in association with each of the one or more steering coils 118 in FIG. 1. These steering coils may also be independently controlled using the control circuitry of FIG. 20. More specifically, the steering coil current source 2014 may comprise a power supply capable of providing DC current to each of the multiple steering coils. The current source may be connected to a steering coil control circuitry 2016 that includes an array of current control elements under the control of a control processor. The steering current control circuitry may thus selectively direct steering currents I1, 12, 13, ... In to the one or more steering coils 118 to control the direction of the electron beam. Methods for controlling the electron beam steering coils are known in the art and will not be described in detail herein. For example, electron beam steering is commonly performed in conventional cathode ray tubes. Nevertheless, it should be understood that the magnitude of the current passed through each steering coil may be selectively controlled to vary the location at which the electron beam strikes the target.

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

[0054] The control processor 2002 may be comprised of one or more devices, such as a computer processor, an application specific circuit, 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 circuit, an integrated circuit (IC), a microcontroller, or a controller formed from discrete components.

[0055] Figures 21A-21C are a series of figures useful in understanding the operation of the DCTAs described herein. For convenience, the DCTAs disclosed herein will be described with reference to Figures 1-8. However, it should be understood that these concepts are equally applicable to many or all of the DCTA structures disclosed herein.

[0056] FIG. 21A conceptually illustrates a composite x-ray beam pattern viewed along the DCTA centerline 416, which can be understood as x-rays being uniformly generated in beam segments 2102 of multiple radially directed beams. Such a beam pattern may be generated when an electron beam is spread or steered to excite all segments 414 associated with a target 402. Each radiation beam segment 2102 is generated by a corresponding beamformer that includes a portion of the DCTA 106. In the scenario illustrated in FIG. 21A, the beamformer is controlled (e.g., by the control system 2000) such that each beam segment provides substantially the same x-ray absorption to a treatment region at different azimuthal directions relative to the DCTA centerline 416. Also, in FIG. 21A, it can be observed that the beam segments 2102 are positioned such 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 generated by a DCTA, such as DCTA 106, is approximately proportional to the square of the accelerating voltage. Thus, in some scenarios, the intensity of the generated x-ray beams can be controlled by controlling the potential of the cathode relative to the anode, respectively. Independent control of the intensity and direction of each x-ray beam segment 2102 can facilitate selective changes in the composite beam pattern to achieve a composite beam pattern as shown in FIG. 21B. The electron beam intensity and / or dwell time can be selectively varied when impinging on different segments of the target to facilitate a desired radiation treatment plan. FIG. 21C illustrates that in some scenarios, the beam intensity at a particular radial or azimuthal direction can be reduced to substantially zero. In other words, the x-ray beam at a particular radial or azimuthal direction can be essentially disabled to facilitate a particular radiation treatment plan. Control of the beam generator can be facilitated by a control system (such as control system 2000).

[0058] It should be noted that the beam patterns of Figures 21A-21C are simplified patterns presented in two dimensions to facilitate a conceptual understanding of how the beam pattern can be controlled in different radial directions by varying the electron beam intensity and dwell time at different locations on the target. The actual beam patterns generated using this technique will be significantly more complex and will necessarily include a three-dimensional radiation pattern, as shown diagrammatically in Figure 7. Nevertheless, it will be appreciated that an electron beam generated using a higher potential will result in a higher x-ray beam intensity in a particular radial or azimuthal direction, and an electron beam generated using a lower potential will result in a lower x-ray beam intensity in a particular radial or azimuthal direction. Naturally, the total amount of time that the x-ray beam is projected in a particular direction will affect the total radiation delivered in that direction.

[0059] The intensity of the x-rays emitted by a focused electron beam is strongly dependent on the distance away from the focal spot. To control the distance of the tissue treatment volume and modify the penetration power of the x-ray beam, it may be advantageous in the case of IORT to fill at least the interstitial space between the x-ray source and the wound cavity with saline. Such an arrangement is shown in FIG. 22, which shows that the DCTA 106 may be placed within a fluid bladder 2202. The fluid bladder may be an elastic balloon-like member that is inflated with a fluid 2206, such as saline, to fill the interstitial space 2204 between the x-ray source and the tissue wall 2208 (e.g., the tissue wall including the tumor bed). Fluid conduits 2210, 2212 may facilitate the flow of fluid into and out of the fluid bladder. Such an arrangement may help to increase the uniformity of irradiation of the tumor bed by placing the entire tissue wall at a uniform distance from the x-ray source to facilitate a more consistent radiation exposure.

[0060] The production of x-rays in the DCTA 106 can generate a significant amount of heat. Thus, in some scenarios, the DCTA can be provided with a separate coolant flow in addition to the fluid 2206 filling the interstitial space 2204. An example of such an arrangement is shown in FIGS. 23 and 24. FIG. 23 shows a portion of the drift tube 104 and the DCTA 106. A cooling jacket 2300 surrounding the drift tube and DCTA is shown in cross section to reveal multiple coaxial cooling tubes 2302, 2305. FIG. 24 is a cross section of the assembly shown in FIG. 23, taken along lines 24-24. From FIGS. 23 and 24, it can be seen that the multiple coaxial cooling tubes can be configured as a sheath surrounding the DCTA (and a portion of the drift tube) to provide a coolant flow that carries heat away from the DCTA.

[0061] More specifically, the outer coaxial cooling tube 2302 is defined by the interstitial space between the outer sheath 2301 and the inner sheath 2304. The inner coaxial cooling tube 2305 is defined by the inner sheath and an outer surface that includes portions of the drift tube 104 and the DCTA 106. The inner coaxial cooling tube 2305 is maintained in part by protrusions 2306. The protrusions maintain a gap between the inner sheath 2304 and the outer surfaces of the drift tube 104 and the DCTA 106. When the x-ray source is activated, coolant 2303 is flowed under positive pressure through the outer coaxial cooling tube 2302 toward the DCTA 106.

[0062] As shown by the arrows in FIG. 23, the coolant 2303 flows to the end 2307 of the cooling jacket where the nozzle portion 2308 is located. In some scenarios, the nozzle portion 2308 can be integral with the inner sheath 2304 as shown. Alternatively, the nozzle portion can comprise a separate element. The nozzle portion 2308 includes multiple ports arranged to allow the coolant 2303 to flow from the outer coaxial cooling tube 2302 to the inner coaxial cooling tube 2305. The nozzle portion also serves to direct the flow or spray of the coolant over and around the DCTA 106 to provide a cooling effect. This flow, shown by the arrows in FIG. 23, can be in the form of a continuous flow, a spray, or a dripping action, depending on the flow pressure of the coolant and the precise configuration of the nozzle portion. After cooling the DCTA tip, the coolant 2303 flows along a return path defined by the inner coaxial cooling tube 2305 in the space maintained by the protrusions 2306. The coolant 2303 then exits the inner coaxial cooling tube through an exhaust port (not shown in FIG. 23).

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

[0064] Further control over the x-ray radiation pattern can be obtained by selectively varying where the electron beam strikes a particular target segment 414. For example, in Figs. 25A-25D, it can be seen that the beam width of the x-ray beam generated by each beamformer can be adjusted by varying the location where the electron beam strikes a particular target segment. When the electron beam strikes a target segment closest to the centerline of the beam shield 404, a relatively narrow beam is generated by the beam forming section. However, as the beam is gradually moved radially outward from the centerline in Figs. 25B-25D, the resulting x-ray beam becomes gradually wider in the azimuth direction. Thus, the direction and shape of the resulting x-ray radiation intensity pattern can be selectively controlled. It should be noted that the beam patterns in Figs. 25A-25D are simplified two-dimensional patterns presented to facilitate a conceptual understanding of how beam width can be controlled by varying the location where the electron beam strikes a particular target segment. The actual beam patterns generated using this technique will be significantly more complex and will necessarily include a three-dimensional radiation pattern similar to that shown in Fig. 7.

[0065] Figures 26A-B show a similar concept, but with a beam shield having a different configuration. In Figures 26A-B, the beam shield 2504 includes multiple sections 2520 that are semicircular in profile rather than wedge shaped. As shown in Figure 26A, selectively controlling the location where the electron beam intersects the target can help control whether a relatively narrow x-ray beam 2502 or a relatively wide beam 2504 is produced by the beam forming sections. As the beam moves radially outward from the centerline of the beam shield 2504, a wider beam is produced.

[0066] A further effect shown in Figure 26A can involve varying the location at which the electron beam intercepts a target associated with a wall element, effectively providing a further method of steering the direction of the generated x-ray beam. As the electron beam rotates about the outer edge of the compartment, the direction of the x-ray beam changes.

[0067] Referring to FIG. 27, the DCTA 2700 can include a beam shield 2704 including a first portion 2706 disposed adjacent one major surface of a target 2702, and a second portion 2708 disposed adjacent an opposite major surface of the target. The first portion 2706 can be disposed inside a drift tube 2714 in a vacuum environment, and the second portion 2708 can be disposed outside the drift tube. However, in some scenarios, the main portion 2713 of the drift tube 2714 can be constructed of a material that absorbs or attenuates X-rays. In such instances, it may be desirable to select a material that comprises the end 2715 of the drift tube that is more transparent to X-ray radiation compared to the main portion 2713 of the drift tube. In such scenarios, the material that comprises the end 2715 can be selected to be transparent to X-rays. This arrangement allows X-rays emitted within the drift tube 2714 to escape the interior unattenuated, thereby providing the desired therapeutic effect.

[0068] The DCTAs disclosed herein can also be configured to have a structure similar to the DCTA 1900 shown in FIG. 19. The DCTA 1900 includes a tubular body 1920. The tubular body can support a target 1902 at a first end and a coupling ring 1922 at an opposite end. A first portion 1906 of a beam shield 1904 extends from a face of the target to be disposed within the tubular body 1920. The coupling ring is configured such that the DCTA 1900 is secured to an end of a drift tube (e.g., the drift tube 104). The coupling ring can facilitate a vacuum seal with the end of the drift tube. Thus, the interior of the tubular body 1920 can be maintained at the same vacuum pressure as the interior of the drift tube.

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

[0070] While the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon reading and understanding this specification and the accompanying drawings. In addition, while a particular feature of the invention may be disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations, as may be desirable and advantageous for a given or particular application.

[0071] The terminology used herein is intended to describe particular aspects of the systems and methods described herein and is not intended to limit the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms "including," "includes," "having," "has," "with," or variations thereof are used anywhere in the detailed description and / or claims, such terms are intended to be inclusive in a similar manner as the term "comprising."

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

Claims

1. generating an electron beam; disposing a plurality of hollow pedestals in a path of the electron beam, the plurality of hollow pedestals being radially spaced apart from one another and extending from a major planar surface of a base plate; generating x-ray radiation as a result of interaction of the electron beam with at least one target element disposed at each hollow end of the plurality of hollow pedestals; interacting the x-ray radiation with a beam shield including a plurality of wall elements extending from a major planar surface of the base plate to form an x-ray beam; and 23. A method for generating x-ray photons, comprising adjusting at least one of a beam shape and a direction of the x-ray radiation by selectively controlling a location at which the electron beam intersects the at least one target element to determine an interaction of the x-ray radiation with the plurality of wall elements.

2. The method of claim 1 , further comprising forming the at least one target element from a material selected from the group consisting of molybdenum, gold, and tungsten.

3. 2. The method of claim 1, further comprising passing the electron beam through an elongated hollow hole in a drift tube, then through an opening formed in the base plate, and into one of the plurality of hollow pedestals.

4. The method of claim 3 , further comprising: causing the x-ray radiation to interact with a beam shield comprising the plurality of wall elements within an x-ray transparent cap disposed at an end of the drift tube.

5. The method of claim 4 , wherein the x-ray transparent cap defines an interior chamber disposed to receive the plurality of wall elements and extends in a direction aligned with a hollow bore of the drift tube.

6. The method of claim 1 , further comprising providing a vacuum environment within each of the plurality of hollow pedestals.

7. The method of claim 1 , wherein a plurality of the target elements are disposed at respective hollow ends of the plurality of hollow pedestals.

8. The method of claim 1 , wherein each of the plurality of hollow pedestals is aligned with one of a plurality of openings formed in the base plate and is located at least partially between two of the plurality of wall elements.

9. The method of claim 1 , further comprising arranging the plurality of wall elements to extend radially outward from a center of a major planar surface of the base plate.

10. Each wall element of the plurality of wall elements comprises: (i) a first surface extending adjacent to the base plate in a radial direction outward from a center of the base plate to points at or near a periphery of the base plate; (ii) the wall elements include planar structures that extend away from a plane of the base plate such that the wall elements are disposed in a plane that is orthogonal to another plane that is at an angle to a direction of a path of the electron beam; The method of claim 1 , wherein (iii) the base plate contacts all others of the plurality of wall elements at a center thereof.

11. Electron beam generator; a base plate having a major planar surface; a plurality of hollow pedestals radially spaced apart from one another and extending from a major planar surface of said base plate; at least one target element disposed at a hollow end of each of the plurality of hollow pedestals and configured to generate x-ray radiation in response to the electron beam generated by the electron beam generator; and a beam shield including a plurality of wall elements extending from a major planar surface of the base plate; Equipped with an x-ray source, wherein at least one of a beam shape and a direction of the x-ray radiation is determined by an interaction of the electron beam with the at least one target element and an interaction of the x-ray radiation with the plurality of wall elements;

12. 12. The x-ray source of claim 11, wherein the at least one target element is constructed from a material selected from the group consisting of molybdenum, gold, and tungsten.

13. 12. The x-ray source of claim 11, further comprising a drift tube partially defining a vacuum chamber, the drift tube having an elongated hollow bore aligned with the direction of the electron beam generated by the electron beam generator.

14. 14. The x-ray source of claim 13, wherein the electron beam passes through the elongated hole in the drift tube, then passes through an opening formed in the base plate, and enters one of the plurality of hollow pedestals.

15. 14. The x-ray source of claim 13, wherein at least one of the plurality of wall elements is disposed within a chamber defined by an x-ray transparent cap located at an end of the drift tube.

16. The x-ray source of claim 13 , wherein the vacuum chamber is at least partially sealed by the base plate.

17. The x-ray source of claim 11 , wherein each of the plurality of hollow pedestals comprises an interior capable of providing a vacuum environment.

18. The x-ray source of claim 11 , wherein a plurality of the target elements are disposed at respective hollow ends of the plurality of hollow pedestals.

19. 12. The x-ray source of claim 11, wherein each of the plurality of hollow pedestals is disposed in one of a plurality of openings formed in the base plate and is located at least partially between two of the plurality of wall elements.

20. Each wall element of the plurality of wall elements comprises: (i) a first surface extending adjacent to the base plate in a radial direction outward from a center of the base plate to points at or near a periphery of the base plate; (ii) the wall elements include planar structures that extend away from a plane of the base plate such that the wall elements are disposed in a plane that is orthogonal to another plane that is at an angle to a direction of a path of the electron beam; 12. The x-ray source of claim 11, wherein (iii) the base plate contacts all others of the plurality of wall elements at a center thereof.

Images