High dose rate radiotherapy systems and targets

Abstract

A radiotherapy machine (100) includes an X-ray target assembly (50) configured to convert an electron beam (45) into an X-ray beam, the X-ray target assembly including, a first target (350-1) configured to disperse at least a portion of the electron beam, and a second target (350-2) configured to convert the portion of the electron beam into the X-ray beam, a thickness (TH-2) of the second target (350-2) being greater than a thickness (TH-1) of the first target (350-1).

Description

HIGH DOSE RATE RADIOTHERAPY SYSTEMS AND TARGETSTECHNICAL FIELD

[0001] One or more example embodiments relate to targets and / or radiotherapy systems including the same, in particular, though not exclusively to X-ray target assemblies and radiotherapy systems comprising an X-ray target assembly.BACKGROUND

[0002] External beam radiation therapy may be used in the treatment of various cancers and non-malignant conditions. Generally, ionizing radiation, including, for example, photons, e.g., X-rays, gamma rays, and charged particles, e.g., protons and electrons, is directed at an area of interest. In many cases, such ionizing radiation is generated by a linear accelerator or a cyclotron.

[0003] Ultra-high dose rate (UHDR) radiotherapy is an emerging radiotherapy regime that appears to reduce radiation-induced toxicides while maintaining a tumor response similar to that of more conventional radiotherapy regimes - known as FLASH effect. UHDR radiotherapy may be characterized as delivering a high radiation rate, e.g., greater than about 40 Grays (Gy) per second, that allows for a total radiotherapy treatment dose, or large fractions of a total radiation dose, to be delivered in parts of a second, compared to several minutes for conventional radiotherapy. For example, a conventional radiotherapy treatment may include a total dose of 2-25 grays (Gy) delivered at a rate of up to 0.4 Gy / s, requiring minutes of treatment time. In contrast,UHDR radiotherapy may deliver a similar total dose at a rate of 40 Gy / s, requiring a fraction of a second of treatment time.

[0004] However, generating such high dosage radiotherapy uses an increase in instantaneous dose rates of several orders of magnitude in comparison to conventional instantaneous dose rates. For example, an instantaneous dose rate of UHDR radiotherapy may be 100 times or more higher than an instantaneous dose rate used in conventional radiotherapy. For FLASH photon (X-ray) radiotherapy, this uses corresponding increases in the electron currents impacting an X-ray target.SUMMARY

[0005] The scope of protection sought for various example embodiments is set out by the appended set of claims. The example embodiments and / or features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments.

[0006] Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.

[0007] According to at least one example embodiment, the present invention provides a radiotherapy system comprising an X-ray target assembly configured to convert an electron beam into an X-ray beam, the X-ray target assembly including a first target configured to disperse at least a portion of the electron beam, and a second target configured to convert the portion of the electron beam into the X-ray beam, a thickness of the second target being greater than a thickness of the first target.

[0008] According to at least one example embodiment, the present invention provides an X-ray target assembly configured to convert an electron beam into an X-ray beam, the X-ray targetassembly comprising a first target configured to disperse at least a portion of the electron beam; and a second target configured to convert the portion of the electron beam into the X-ray beam, a thickness of the second target being greater than a thickness of the first target.

[0009] Suitably, the X-ray target of the present invention comprises multiple layers of spatially separated targets. The first and second targets are suitably arranged in series along the central axis of the electron beam. Suitably, the first target comprises one or a plurality of first target layers, wherein each of the one or more first target layers is thinner than the second target. The plurality of target layers may be separated by a constant distance, by a variable distance or by an adjustable distance.

[0010] Suitably, each of the one or more first target comprises a foil, a plate, a wire, a set of wires or a mesh. The first target may have any shape suitable to achieve the desired beam spot shape. For example, the first target may be rectangular or the first target may comprise a plurality of overlapping geometrical shapes, such as a plurality of overlapping triangles. The first target may comprise one or more slits, extending through the thickness thereof. The thickness of the first and second target layers is measured in the direction of the central axis of the electron beam. The thickness of each target layer may be constant. Alternatively, the thickness of each target may vary. The thickness of each target may depend upon the material from which they are made. When the first target comprises a plurality of layers, each first target layer may have a thickness of around 0.1mm. The first target suitably has a thickness of less than 1 cm. The second target may have a thickness of be from 1 mm to 1 cm.

[0011] The first target may comprise tantalum or tungsten or a combination of tantalum and copper or a combination of tungsten and copper. The first target may include brass. When the first target comprises a plurality of layers, each layer may be the same material, or the differentlayers may comprise different materials. The second target may comprise at least one refractory material. Suitable refractory materials have an atomic number of 42 or greater. For example, the refractory material may be molybdenum, tungsten, tantalum, gold or antimony.

[0012] According to at least one example embodiment, the present invention provides a radiotherapy system comprising an X-ray target assembly configured to convert an electron beam into an X-ray beam, the X-ray target assembly including a first means configured to disperse at least a portion of the electron beam, and a second means configured to convert the portion of the electron beam into the X-ray beam, a thickness of the second means being greater than a thickness of the first means.

[0013] An X-ray target assembly according to the present invention may further comprise heat management comprising one or more cooling mechanism. Suitable cooling mechanisms may include heat sinks, air cooling, radiative transfer, water cooling or high-pressure water cooling. In an embodiment, a radiotherapy system is provided wherein at least one cooling apparatus is coupled to the second target and configured to supply a cooling fluid to the second target.

[0014] A radiotherapy system according to the present invention may be configured to control the electron beam such that the X-ray beam delivers a radiation rate of at least 40 grays per second (Gy / s). In other embodiments, a radiotherapy system according to the present invention is configured to control the electron beam such that the X-ray beam delivers a radiation rate of less than 40 grays per second (Gy / s). The X-ray target assembly may be configured to absorb at least 99% of electrons of the electron beam incident on the first target. The second target may be configured to absorb at least 90% of electrons of the dispersed electron beam.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Example embodiments will become more fully understood from the detailed description given herein below and the accompanying drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus are not limiting of this disclosure.

[0016] FIG. 1 illustrates a block diagram of a radiation treatment system in accordance with example embodiments.

[0017] FIG. 2 illustrates a side- sectional schematic representation of an exemplary beam path in the radiation treatment system of FIG. 1, in accordance with example embodiments.

[0018] FIG. 3 illustrates a side view of an X-ray target according to one or more example embodiments.

[0019] FIG. 4A illustrates a target and corresponding electron beam spot.

[0020] FIGS. 4B-4E illustrate target assemblies and corresponding electron beam spots according to one or more example embodiments.

[0021] FIGS. 5A-5C illustrate a target assembly according to one or more example embodiments.

[0022] FIG. 6 illustrates a block diagram of a control system with which embodiments may be implemented.

[0023] It should be noted that these figures are intended to illustrate the general characteristics of methods, structure and / or materials utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment and should not be interpreted as defining or limiting the range of values or properties encompassed byexample embodiments. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature.DETAILED DESCRIPTION

[0024] Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are shown.

[0025] Detailed illustrative embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

[0026] It should be understood that there is no intent to limit example embodiments to the particular forms disclosed. On the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of this disclosure. Like numbers refer to like elements throughout the description of the figures.

[0027] As discussed herein the terminology “one or more” and “at least one” may be used interchangeably.

[0028] It will be appreciated that a number of example embodiments may be used in combination.

[0029] Although one or more example embodiments may be discussed herein with regard to an embodiment of an X-ray target positioned in a treatment head of a radiotherapy system, it should be understood that example embodiments should not be limited to such examples. Rather, an X-ray target described may also be deployed as an accessory to the treatment head.

[0030] To produce photon Flash radiotherapy, a high current electron beam is converted tophotons in a Bremsstrahlung target. Typical static tungsten targets are damaged by the heat generated by the increased beam current required to produce the dose rate of photons (e.g., 40 Gy / s). The thermal strain on the target is held to a manageable level to ensure the target can produce photons at ultra-high dose rates.

[0031] A number of solutions to lower the target thermal strain have been proposed. One option is to increase the beam energy which increases Bremsstrahlung production efficiency in the target, but also increases the shielding, power and cooling requirements for the linear accelerator (linac). Alternatively, one could move the target so the electron beam impacts a different material volume of the target with each subsequent pulse.

[0032] Increasing an electron beam spot size on the target improves heat dissipation and reduces thermal strain on the target. A measure to do this would allow for a smaller beam spot size at the target at, e.g., lower dose rates and / or higher energies, where a target can produce sufficient output without sacrificing the x-ray target life span, but also enlarge the beam spot size easily where used for lower energy and / or higher dose rate beams.

[0033] The inventors have discovered a thin target or foil, or series of thin targets or foils upstream of the main, thicker target would allow for an increased electron beam spot size for higher dose rate beams. These thin targets may completely cover the electron beam or be a series of shaped metal, wires, or slits to enable arbitrary beam shaping without or supplemented by a downstream multi-leaf collimator.

[0034] FIG. 1 illustrates a block diagram of a radiation treatment system in accordance with example embodiments.

[0035] FIG. 1 illustrates a block diagram of an exemplary radiation treatment system 100 that may serve as a platform for example embodiments. Radiation treatment system 100 may be similarto aTrueBeam® radiotherapy system, commercially available from Varian Medical Systems, Palo Alto, CA.

[0036] A stand 10 supports a rotatable gantry 20 with a treatment head 30. The treatment head 30 may extend into the gantry 20. In proximity to the stand 10 there is arranged a control unit 18 which includes control circuitry for controlling the different modes of operation of the system 100.

[0037] The radiation treatment system 100 comprises a linear accelerator (linac) 40, for example, within the gantry 20, utilized to create a radiation beam. Typically, the radiation treatment system 100 is capable of generating either an electron (particle) beam or an X-ray (photon) beam for use in the radiotherapy treatment of patients on a treatment couch 35. Other radiation treatment systems are capable of generating light ion particles such as protons, alpha particles, or carbon ions. For purposes of the following disclosure, only X-ray (photon) irradiation will be discussed.

[0038] A high voltage source is provided within the stand and / or in the gantry to supply voltage to an electron gun (not shown) positioned on an accelerator guide located in the gantry 20. Electrons are emitted from the electron gun into the accelerator 40 where they are accelerated. A source supplies radio frequency (microwave) power for the generation of an electric field within the waveguide. The electrons emitted from the electron gun are accelerated in the waveguide by the electric field, and exit the waveguide as a high-energy electron beam 45, for example, at megavoltage energies. The electron beam 45 may pass through a set of bending plane scan magnets 47, in some embodiments. The electron beam 45 may pass through a set of bend magnets 49, to redirect the electron beam 45 from substantially horizontal to substantially vertical, in some embodiments. The electron beam 45 then enters a drift tube 52 and strikes a suitable X-ray target 50, for example, a Bremsstrahlung transmission target, converting a portion of the electron beam 45 into X-rays (photons) 55 in the direction of a patient P. The drift tube 52 reduces scatteringbefore striking the target 50 and effectively reduces a source to surface distance (SSD) between a treatment surface and the target 50. The SSD may be measured from a top of the target 50, a middle of the target 50, a bottom of the target 50 or any other location in the target 50.

[0039] As illustrated in FIG. 1, a patient P is shown lying on the treatment couch 35. High energy photons as described above are emitted from the treatment head 30 in a divergent beam 104. Typically, a patient plane 116. is positioned, for example, about one meter from the X-ray source, and the rotational axis of the gantry 20 is located on the patient plane 116, such that the distance between the target 50 and the isocenter 178 remains constant when the gantry 20 is rotated. It is appreciated that for photon FLASH therapy, the patient plane 116 may be less than one meter from the electron source. The isocenter 178 is at the intersection between the axis of rotation of the gantry 20 and the central axis of beam 122. A treatment volume to be irradiated may be located about the isocenter 178, or in some embodiments may be located closer to or farther from the treatment head 30. It is appreciated that some treatment plans may utilize a primary treatment target that is off of the central beam axis, and such arrangements are within the scope of example embodiments.

[0040] FIG. 2 illustrates a side- sectional schematic representation of an exemplary beam path 200 within the radiation treatment system 100, in accordance with example embodiments. It is appreciated that the illustrated components of the beam path 200 are exemplary, and all may not be required in some embodiments. Additional components, e.g.. a flattening filter (not shown), may also be included in accordance with embodiments of the present invention. Prior to impinging the X-ray target 50, the electron beam 45 may pass through a set of cross plane scanning magnets 201, in some embodiments. As previously presented, the electron beam 45 impinges on the X-ray target 50 producing the X-ray radiation beam 210.

[0041] The radiation beam 210 passes through a monitor chamber 250, sometimes known or referred to as an “ion chamber.” The monitor chamber 250 functions to measure a radiotherapy dose. X and Y jaws 260, and leaves of a multi-leaf collimator (MLC) 270 function to shape radiation beam 210 to a desired shape and / or beam profile for patient treatment. In addition or alternatively, as will be described in more detail below, a thin target may be used to modify the electron beam spot and also the distribution of the fluence of electrons within that spot.

[0042] A primary collimator 220 may comprise a plurality of selectable collimators and / or filters, in some embodiments. The primary collimator 220, typically comprises an X-ray blocking material, and may be positioned in the head 30 (FIG. 1) to define the width of the X-ray beam at the patient plane. Typically, the X and Y jaws 260 are moveable and, when fully open, define a maximum beam width at the patient plane 116 (FIG. 1). The MLC 270 may be positioned at the exit of the head 30, to further shape the X-ray beam. Exemplary MLCs may use up to 120 individually controllable leaves, for example, thin slices of tungsten, which may be moved into or out of the X-ray beam under the control of system software.

[0043] As a high-energy electron beam, e.g., 22 MeV passes through an X-ray target, e.g., Tungsten (W) or Tantalum (Ta), the linear energy transfer (LET) dictates the heat generation profile within the target. LET refers to the energy that an ionizing particle transfers to the material per unit distance traveled. In some example embodiments, the X-ray target may include at least two materials, e.g.. Tungsten and copper or Tantalum and copper. As the electron beam penetrates deeper into the target material, the LET gradually increases, reaching a maximum at a critical thickness. Beyond this critical thickness, the stopping power becomes excessively high, leading to a rapid absorption of beam energy. For 22 MeV for example, the critical thickness for W / Ta is approximately 1.15 mm.

[0044] The X-ray target 50 is designed to include multiple layers of spatially separated targets ensuring (i) heat dissipation for a beam incident on a thicker target and ii) >99% of the incident electrons lose all of their energy (are absorbed) in the X-ray target 50.

[0045] In accordance with example embodiments, the X-ray target 50 is configured to operate in UHDR radiotherapy and absorb >99% of the incident electrons. In accordance with other example embodiments, the X-ray target 50 is also configured to operate in ultra-high dose rate (UHDR) radiotherapy, e.g., at least 1 Gray (Gy) per second and absorb >99% of the incident electrons. Additionally or alternatively, the X-ray target 50 is configured to operate with conventional dose rate beams (e.g., <.40 Gy / s).

[0046] FIG. 3 illustrates a side view of an X-ray target according to one or more example embodiments.

[0047] As shown in FIG. 3, the X-ray target 50 includes two target layers 350-1 to 350-2. Each of the plurality of target layers 350-1 to 350-2 is configured to convert a portion of the electron beam 45 into a portion of the radiation beam 210. While only two layers are shown, it should be understood that the target layer 350-1 may be divided into a plurality of target layers.

[0048] The target layer 350-1 (a first target) may be a thin target and the target layer 350-2 (a second target) may be a thick target (i.e., a thickness TH-2 of the target layer 350-2 is larger than a thickness TH-1 of the target layer 350-1). The target layer 350-1 can act as a scattering foil and is configured to disperse at least a portion of the electron beam 45. The thin target layer 350-1 spreads out the electron beam spot for better heat dissipation when it impacts the thick target layer 350-2. The thick target layer 350-2 is configured to convert the portion of the electron beam 45 into the X-ray beam 104. In some example embodiments, the thick target layer 350-2 is thickenough to absorb at least 99% of electrons of the electron beam incident on the thick target layer 350-2 (e.g., all electrons).

[0049] The thickness TH-1 of the target layer 350-1, composition and position relative to the target layer 350-2 (e.g., the Bremsstrahlung) can be optimized to produce the desired beam spot.

[0050] In some example embodiments, the plurality of target layers 350-1 to 350-2 are stacked in series, e.g., along the central axis of the beam 122. However, example embodiments are not limited thereto. Moreover, the plurality of target layers 350-1 to 350-2 may be separated by a constant distance or an adjustable distance.

[0051] In some example embodiments, the target layer 350-1 may be a foil or plate and include brass. In some example embodiments, the thickness TH-1 of the target layer 350-1 is less than 1 cm and may be constant.

[0052] If changes in beam spot shape are desired, the target layer 350-1, may be shaped to, e.g., scatter only part of the electron beam or as a series of slits to optimize beam spot shape. The electron beam at the target layer 350-1 is smaller than the beam at layer target 350-2 because the target layer 350-1 will spread the electron beam out. The target layer 350-1 may be a foil, covering the whole electron beam, and in other example embodiments the first target 350-1 is, e.g., a wire configured to spread the electron beam in one dimension only.

[0053] In other example embodiments, the target layer 350-1 may be a foil or plate with a variable thickness. With a variable thickness, the target layer 350-1 produces a beam spot with a desired shape on the target layer 350-2. A penumbra (a fall off at an edge of the electron beam) depends on the spot size and shape of the beam. Using the target layer 350-1 allows refinement of the penumbra and beam shaping. For Flash beams, the beam spot may be larger for heat dissipation in the target layer 350-2. Thus, in some example embodiments for Flash beams, thetarget layer 350-1 may be designed to be a particular shape to reduce the impact of the larger spot size on patient treatment plans.

[0054] The desired shape may be a 2D electron beam pattern.

[0055] In other example embodiments, the target layer 350-1 may be a wire or a set of wires instead of a plate or foil.

[0056] The target layers 350-2 may comprise at least one refractory metal. Refractory metals are characterized as a high Z materials, e.g., materials comprising elements with a high atomic number (“Z”) of protons in the nucleus, and having a high melting temperature. As used herein, “high-Z” refers to or describes elements having an atomic number of 42, corresponding to molybdenum (Mo), or greater. Exemplary elements include tungsten (W), tantalum (Ta), molybdenum (Mo), gold (Au), and / or antimony (Sb). The total thickness of the target layers 350-1 to 350-2 is selected to be sufficient to generate the required dose of X-rays, while minimizing attenuation and energy loss of the incident high-energy electrons.

[0057] FIG. 4A illustrates a target and corresponding electron beam spot. FIGS. 4B-4E illustrate target assemblies and corresponding electron beam spots according to one or more example embodiments.

[0058] FIG. 4A illustrates a target 350 as a single layer. As shown, the electron beam 45 strikes the target 350 without any intermediary layer. Due to the absence of an intermediary layer (e.g., the first target layer 350-1), a concentrated beam spot 405a occurs on the target 350. As described above, heat dissipation is reduced and reduce thermal strain on the target 350 is increased relative to using an intermediary target layer. In FIGS. 4A-4E, a darker shade in a particular beam spot reflects an increased number of electrons striking the target relative to a lighter shade in the particular beam spot.

[0059] FIG. 4B illustrates the target assembly includes two target layers 350-1 a and 350-2. The target assembly shown in FIG. 4B may be the same as the target assembly shown in FIG. 3. The target layer 350-la may be a rectangular thin foil target. As shown in FIG. 4B, the electron beam 45 strikes the target layer 350-la, which causes the electron beam to spread out in all directions of two dimensions defined by the length and width of the of target layer 350-la. This results in an electron beam 45a that hits the target layer 350-2 and forming a beam spot 405b. As shown, the beam spot 405b is spread out in a radial direction relative to the beam spot 405a, resulting in improved heat dissipation and reduced thermal strain on the target layer 350-2.

[0060] FIG. 4C illustrates the target assembly includes two target layers 350-lb and 350-2. The target layer 350-lb may be a target in the shape of a wire. As shown in FIG. 4C, the electron beam 45 strikes the target layer 350-lb, which causes the electron beam to spread out, primarily along the longitudinal axis of the target layer 350-lb. This results in an electron beam 45b that hits the target layer 350-2 and forming a beam spot 405c. As shown, the beam spot 405c is spread out along the longitudinal axis of the target layer 350-lb relative to the beam spot 405a, resulting in improved heat dissipation and reduced thermal strain on the target layer 350-2.

[0061] FIG. 4D illustrates the target assembly includes two target layers 350-lc and 350-2. The target layer 350-lc may be a target having three overlapping triangular foils 450. As shown in FIG. 4D, the electron beam 45 strikes the target layer 350-lc, which causes the electron beam to spread out based on the shape of the target layer 350-lc. This results in an electron beam 45c that hits the target layer 350-2 and forming a beam spot 405d. As shown, the beam spot 405d is spread out relative to the beam spot 405a, resulting in improved heat dissipation and reduced thermal strain on the target layer 350-2. Beamlets within the electron beam 45 are spread and energy attenuated based on the thickness and composition of the target layer 350-1 they interact with,resulting in a complex patter of electron beam spot shape and fluence on the thick target 350-2. Moreover, areas of the beam spot 405d that correspond the overlapping portions of the triangular foils 450 are impacted by a lower number of electrons than the areas of the beam spot 405d that do not correspond to the overlapping portions.

[0062] FIG. 4E illustrates the target assembly includes two target layers 350-ld and 350-2. The target layer 350-ld may be a rectangular thin foil target with 2 slits across a width of the target layer 350-ld. As shown in FIG. 4E, the electron beam 45 strikes the target layer 350-ld, which causes the electron beam to spread out based on the shape of the target layer 350-ld. In addition, due to the slots, electrons are not dispersed if they pass through one of the two slits. This results in an electron beam 45d that hits the target layer 350-2 and forming a beam spot 405e. As shown, the beam spot 405e is spread out relative to the beam spot 405a, resulting in improved heat dissipation and reduced thermal strain on the target layer 350-2. Moreover, areas of the beam spot 405e that correspond the slots are impacted by a higher number of electrons than the areas of the beam spot 405e that do not correspond to the slots.

[0063] It should be understood that the target layer 350-1 is not limited to the shapes shown in FIGS. 4B-4E and other shapes may be used to create a desired beam spot on the target layer 350-2.

[0064] Referring back to FIG. 3. in some example embodiments, each of the target layers 350-1 to 350-n is .1 mm for an X-ray target 50 comprising Tantalum (Ta) or Tungsten (W). In some example embodiments, each of the target layers 350-1 to 350-n may be the same material.

[0065] In some example embodiments, the thickness TH-2 of the target layer 350-2 may be the same thickness as a single piece target such as 1 mm for an X-ray target 50 comprising Ta.

[0066] For example, an exemplary UHDR radiotherapy treatment may use an electron energy of at least 50 MeV, producing up to 25 kW of average beam power.

[0067] As attenuation of high-energy electrons within the X-ray target 50 produces heat, the target layer 350-1 spreads out the electron beam spot for better heat dissipation when it impacts the target layer 350-2. Reducing heating of the target layer 350-2 improves the stability and reliability of a UHDR radiotherapy system.

[0068] The spacing of the target layers 350-1 to 350-2 in series along the electron beam path allows for heat management through at least one of heat sinks, air cooling, radiative transfer, or (high-pressure) water cooling and an increased beam spot size on the target layer 350-2. For example, the target 50 may be used with the cooling system described in U.S. Patent No. 8,761,347, the entire contents of which are incorporated by reference. The spacing of the target layer 350-1 to 350-2 can be paired with existing heat management solutions involving a moving target or scanning beam such as described in U.S. Patent No. 12,186,587, the entire contents of which are incorporated by reference. Moreover, by maintaining the thickness of the target layer 350-2 to be the same as a single piece target, the electrons are stopped within the target layer 350-2, resulting in no need for additional electron contamination management.

[0069] FIG. 5A is a perspective view of an exemplary target assembly 500 in accordance with some example embodiments. The target assembly 500 positions a target in the beam path for generation of X-rays in a photon mode, or moves a target out of the beam path in an electron mode. The target assembly 500 includes a channel mount 502, a substrate 504 supporting one or more target buttons 506 and a cooling tube 508 coupled to the substrate 504 for supplying a cooling fluid. At least one of the one or more target buttons 506 may be the target 50. Channels can be provided in the substrate 504 adjacent or surrounding the target buttons 506 for circulating acooling fluid to dissipate heat generated during target operation. The substrate 504 and the cooling tube 508 can be supported by a mount assembly 510, which is movable relative to the channel mount 502.

[0070] The target assembly 500 and cooling tube 508 are further described in U.S. Patent No.8,761,347, the entire contents of which are incorporated by reference.

[0071] Thus, the target 50 may be used with existing cooling mechanisms.

[0072] FIGS. 5B-5C illustrate at least one example embodiment using a plurality of cooling tubes. FIG. 5B illustrates a cross-sectional view of the target assembly 50. In some example embodiments, a plurality of cooling tubes 508-1 and 508-2 may be used for the target layers 350-1 and 350-2, respectively, as shown in FIGS. 5B-5C.

[0073] As shown in FIG. 5B, each of the target layers 350-1 to 350-2 is placed in a corresponding heat sink layer 504-1 to 504-n. More specifically, each heat sink layer 504-1 to 504-n has a receiving area 520 with a diameter that is the same or slightly larger than the target layer 350 corresponding to the heat sink layer 504-1 to 504-n.

[0074] Each of the layers includes a cooling tube 508.

[0075] The target assembly 500 may include a plurality of slots to accommodate a varying number of target layers. For example, the target assembly may have n slots and n cooling tubes. Based on the energy level of the beam 45, a selected number of target and heat sink layers may be inserted into the n slots. The selected number may be n or less than n. Each of the slots may have a defined mounting for a target and heat sink layer. Moreover, while the combination of a layer is described as a target and heat sink layer, it should be understood that the slots may accommodate a combination target layer and heat transfer material layer and / or a combination of the target layer, heat transfer material layer and heat sink layer.

[0076] FIG. 5C illustrates a top view (e.g., beam-eye view) of the first layer. The remaining layers are the same, with the exception of the size of the target layer within the corresponding layer.

[0077] As shown in FIG. 5C, the cooling tube 508-1 supplies water (or another cooling liquid) to a cooling channel 550 through a coupling 530. The cooling channel 550 and the coupling 530 may be embedded in the heat sink layer 504-1. The cooling channel 550 may have a general u-shape. A curved portion 555 of the U-shaped cooling channel 550 may have a curvature that matches the curvature of the target layer 350-1. However, example embodiments are not limited thereto and the cooling channel 550 may have a different shape.

[0078] Moreover, each of the couplings 530 may include valve that is operable based on whether a target and heat sink layer is being used in a slot. For example, if a target and heat sink layer is present in the slot, the valve is open to allow the flow of water through a channel in the heat sink layer. If no target and heat sink layer is present in the slot, the corresponding valve is closed.

[0079] In other example embodiments, the cooling system may be provided for the thicker target layer 350-2 and not the layer 350-1. In the thin target 350-1, there is less heat deposited so a cooling system may not be used.

[0080] Referring back to FIG. 5A, the target assembly 500 can be moved by a linear axis 514, which includes a motor 514a. a ball screw, a coupler 514b coupling the motor and the ball screw, and a ball nut 514c engaging the ball screw.

[0081] The target assembly 500 may include one or more targets each being optimized to match the energy of an incident electron beam. For example, the target assembly 500 may include a first target 506a adapted for a first photon mode, a second target 506b for a second photon mode and a third target 506c for a third photon mode. It should be noted that a different number of targetsmay be included in the target assembly 500. In operation, the linear axis 514 moves or positions one of the targets 506 in the beam path for a photon mode. In an electron mode, the linear axis 514 removes the targets 506 out of the beam path to allow an electron beam passes unimpeded.

[0082] It should be noted that a different number of targets may be included in the target assembly 500. In operation, the linear axis 514 moves or positions one of the targets 506 in the beam path for a photon mode. In an electron mode, the linear axis 514 removes the targets 506 out of the beam path to allow an electron beam passes unimpeded.

[0083] FIG. 6 illustrates a block diagram of a control system with which embodiments may be implemented.

[0084] In some embodiments, a control system 600 shown in FIG. 6 may be used to implement the control unit 18. The control system 600 may also be an example of any control system described herein.

[0085] The control system 600 includes a bus 602 or other communication mechanism for communicating information, and processing circuitry 604 (e.g., at least one processor and / or ASIC) coupled with the bus 602 for processing information. In examples where the processing circuitry 604 is hardware configured to executed stored instructions (e.g., a processor), the control system 600 also includes a main memory 606, such as a random-access memory (RAM) or other dynamic storage device, coupled to the bus 602 for storing information and instructions to be executed by the processing circuitry 604. The main memory 106 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processing circuitry 604. The control system 600 further includes a read only memory (ROM) 608 or other static storage device coupled to the bus 602 for storing static information and instructions for the processing circuitry 604. A data storage device 610, such as amagnetic disk or optical disk, may be provided and coupled to the bus 602 for storing information and instructions.

[0086] The control system 600 may be coupled via the bus 602 to a display 612, such as a flat panel, for displaying information to a user. An input / output device 614, such as a touchscreen, is coupled to the bus 602 for communicating information and command selections to processing circuitry 604. Another type of user input device is cursor control 616, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processing circuitry 604 and for controlling cursor movement on display 612. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane.

[0087] While the display 612 and I / O device 614 are shown outside of the control system 600, it should be understood that the display 612 and the I / O device 614 are part of the control system 600. Moreover, while the display 612, the I / O device 614 and the curser control 616 are illustrated as separate components, it should be understood that they may be combined, such as a touch screen display.

[0088] In some embodiments, the control system 600 can be used to perform various functions described herein. According to some embodiments, such use is provided by control system 600 in response to the processing circuitry 604 executing one or more sequences of one or more instructions contained in the main memory 606. Those skilled in the art will know how to prepare such instructions based on the functions, algorithms and methods described herein. Such instructions may be read into the main memory 606 from another processor-readable medium, such as storage device 610. Execution of the sequences of instructions contained in the main memory 606 causes the processing circuitry 604 to perform the process steps described herein.One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in the main memory 606. In alternative embodiments, hardwired circuitry may be used in place of or in combination with software instructions to implement the various embodiments described herein. Thus, embodiments are not limited to any specific combination of hardware circuitry and software.

[0089] Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise the bus 602. Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications.

[0090] Various forms of processor-readable media may be involved in carrying one or more sequences of one or more instructions to the processing circuitry 604 for execution. For example, the instructions may initially be earned on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a network, such as the Internet or a local network. A receiving unit local to the control system 600 can receive the data from the network and provide the data on the bus 1602. The bus 602 carries the data to the main memory 606, from which the processing circuitry 604 retrieves and executes the instructions. The instructions received by the main memory 606 may optionally be stored on the storage device 610 either before or after execution by the processing circuitry 604.

[0091] The control system 600 also includes a communication interface 618 coupled to the bus 602. The communication interface 618 provides a two-way data communication coupling to a network link 620 that is connected to a local network 622. For example, the communication interface 618 may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, the communication interface 618 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, the communication interface 618 sends and receives electrical, electromagnetic or optical signals that carry data streams representing various types of information.

[0092] The network link 620 typically provides data communication through one or more networks to other devices. For example, the network link 620 may provide a connection through local network 622 to a host computer 624 or to equipment 626 such as a radiation beam source or a switch operatively coupled to a radiation beam source. The data streams transported over the network link 620 can comprise electrical, electromagnetic or optical signals. The signals through the various networks and the signals on the network link 620 and through the communication interface 618, which carry data to and from the control system 600, are exemplary forms of carrier waves transporting the information. The control system 600 can send messages and receive data, including program code, through the network(s). the network link 620, and the communication interface 618.

[0093] Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of this disclosure. As used herein, the term "and / or," includes any and all combinations of one or more of the associated listed items.

[0094] When an element is referred to as being "connected," or "coupled," to another element, it can be directly connected or coupled to the other element or intervening elements may be present. By contrast, when an element is referred to as being "directly connected," or "directly coupled," to another element, there are no intervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion (e.g., "between," versus "directly between," "adjacent," versus "directly adjacent," etc.).

[0095] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 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. It will be further understood that the terms "comprises." "comprising," "includes," and / or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0096] It should also be noted that in some alternative implementations, the functions / acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality / acts involved.

[0097] Specific details are provided in the following description to provide a thorough understanding of example embodiments. However, it will be understood by one of ordinary skill in the art that example embodiments may be practiced without these specific details. For example, systems may be shown in block diagrams so as not to obscure the example embodiments in unnecessary detail. In other instances, well-known processes, structures and techniques may be shown without unnecessary detail in order to avoid obscuring example embodiments.

[0098] As discussed herein, illustrative embodiments are described with reference to acts and symbolic representations of operations (e.g., in the form of flow charts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.) that may be implemented as program modules or functional processes include routines, programs, objects, components, data structures, etc., thatperform particular tasks or implement particular abstract data types and may be implemented using existing hardware, for example, processing or control circuitry such as, but not limited to, one or more processors, one or more Central Processing Units (CPUs), one or more controllers, one or more arithmetic logic units (ALUs), one or more digital signal processors (DSPs), one or more microcomputers, one or more field programmable gate arrays (FPGAs), one or more System-on-Chips (SoCs), one or more programmable logic units (PLUs). one or more microprocessors, one or more Application Specific Integrated Circuits (ASICs), or any other device or devices capable of responding to and executing instructions in a defined manner.

[0099] Although a flow chart may describe the operations as a sequential process, many of the operations may be performed in parallel, concurrently or simultaneously. In addition, the order of the operations may be re-arranged. A process may be terminated when its operations are completed, but may also have additional steps not included in the figure. A process may correspond to a method, function, procedure, subroutine, subprogram, etc. When a process corresponds to a function, its termination may correspond to a return of the function to the calling function or the main function.

[0100] As disclosed herein, the term “memory,” "storage medium," “processor readable medium,” "computer readable storage medium" or "non-transitory computer readable storage medium” may represent one or more devices for storing data, including read only memory (ROM), random access memory (RAM), magnetic RAM. core memory, magnetic disk storage mediums, optical storage mediums, flash memory devices and / or other tangible machine-readable mediums for storing information. The term "computer-readable medium" may include, but is not limited to, portable or fixed storage devices, optical storage devices, and various other mediums capable of storing, containing or carrying instruction(s) and / or data.

[0101] Furthermore, example embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine or computer readable medium such as a computer readable storage medium. When implemented in software, a processor or processors will perform the necessary tasks. For example, as mentioned above, according to one or more example embodiments, at least one memory may include or store computer program code, and the at least one memory and the computer program code may be configured to, with at least one processor, cause a network element or network device to perform the necessary tasks. Additionally, the processor, memory and example algorithms, encoded as computer program code, serve as means for providing or causing performance of operations discussed herein.

[0102] The terms “including” and / or “having,” as used herein, are defined as comprising (i.e., open language). The term “coupled,” as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. Terminology derived from the word “indicating” (e.g., “indicates” and “indication”) is intended to encompass all the various techniques available for communicating or referencing the object / information being indicated. Some, but not all, examples of techniques available for communicating or referencing the object / information being indicated include the conveyance of the object / information being indicated, the conveyance of an identifier of the object / information being indicated, the conveyance of information used to generate the object / information being indicated, the conveyance of some part or portion of the object / information being indicated, the conveyance of some derivation of the object / information being indicated, and the conveyance of some symbol representing the object / information being indicated.

[0103] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause or result in such benefits, advantages, or solutions, or cause such benefits, advantages, or solutions to become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims.Non-Limiting Illustrative Embodiments

[0104] Illustrative embodiment 1 includes a radiotherapy system comprising an X-ray target assembly configured to convert an electron beam into an X-ray beam, the X-ray target assembly including a first target configured to disperse at least a portion of the electron beam, and a second target configured to convert the portion of the electron beam into the X-ray beam, a thickness of the second target being greater than a thickness of the first target.

[0105] Illustrative embodiment 2 includes the radiotherapy system of illustrative embodiment 1, wherein the radiotherapy system is configured to control the electron beam such that the X-ray beam delivers a radiation rate of at least 40 grays per second (Gy / s).

[0106] Illustrative embodiment 3 includes the radiotherapy system of any one of illustrative embodiments 1, wherein the radiotherapy system is configured to control the electron beam such that the X-ray beam delivers a radiation rate of less than 40 grays per second (Gy / s).

[0107] Illustrative embodiment 4 includes the radiotherapy system of any one of illustrative embodiments 1-3, wherein the first target and the second target are stacked in series.

[0108] Illustrative embodiment 5 includes the radiotherapy system of any one of illustrative embodiments 1-4, wherein the first target includes a plurality of slits.

[0109] Illustrative embodiment 6 includes the radiotherapy system of any one of illustrativeembodiments 1-5, wherein the first target is rectangular.

[0110] Illustrative embodiment 7 includes the radiotherapy system of any one of illustrative embodiments 1-6, wherein the first target is a wire or a plurality of wires.

[0111] Illustrative embodiment 8 includes the radiotherapy system of any one of illustrative embodiments 1-6, wherein the first target is a foil.

[0112] Illustrative embodiment 9 includes the radiotherapy system of any one of illustrative embodiments 1-8, wherein the first target includes brass.

[0113] Illustrative embodiment 10 includes the radiotherapy system of any one of illustrative embodiments 1-9, wherein the second target includes at least one of tantalum (Ta) or tungsten (W).

[0114] Illustrative embodiment 11 includes the radiotherapy system of illustrative embodiment 8, wherein the foil includes overlapping layers of the foil.

[0115] Illustrative embodiment 12 includes the radiotherapy system of illustrative embodiment 11, wherein the layers are triangular.

[0116] Illustrative embodiment 13 includes the radiotherapy system of any one of illustrative embodiments 1-12, wherein the thickness of the first target is less than 1 cm.

[0117] Illustrative embodiment 14 includes the radiotherapy system of any one of illustrative embodiments 1-13, wherein the thickness of the first target varies.

[0118] Illustrative embodiment 15 includes the radiotherapy system of any one of illustrative embodiments 1-14, further comprising at least one cooling apparatus coupled to the second target and configured to supply a cooling fluid to the second target.

[0119] Illustrative embodiment 16 includes the radiotherapy system of any one of illustrative embodiments 1-15, wherein the X-ray target assembly is configured to absorb at least 99% of electrons of the electron beam, the electron beam incident on the first target.

[0120] Illustrative embodiment 17 includes the radiotherapy system of any one of illustrative embodiments 1-16, wherein the second target is configured to absorb at least 90% of electrons of the dispersed electron beam.

[0121] Illustrative embodiment 18 includes an X-ray target assembly configured to convert an electron beam into an X-ray beam, the X-ray target assembly comprising a first target configured to disperse at least a portion of the electron beam; and a second target configured to convert the portion of the electron beam into the X-ray beam, a thickness of the second target being greater than a thickness of the first target.

[0122] Illustrative embodiment 19 includes the X-ray target assembly of illustrative embodiment 18, wherein the first target and the second target are stacked in series.

[0123] Illustrative embodiment 20 includes the X-ray target assembly of any one of illustrative embodiments 18-19. wherein the first target is a foil.

Claims

1. WHAT IS CLAIMED IS:

1. A radiotherapy system (100) comprising:an X-ray target assembly (50) configured to convert an electron beam (45) into an X-ray beam, the X-ray target assembly including,a first target (350-1) configured to disperse at least a portion of the electron beam, anda second target (350-2) configured to convert the portion of the electron beam into the X-ray beam, a thickness of the second target (350-2) being greater than a thickness of the first target (350-1).

2. The radiotherapy system of claim 1, wherein the radiotherapy system is configured to control the electron beam (45) such that the X-ray beam delivers a radiation rate of at least 40 grays per second (Gy / s).

3. The radiotherapy system of claim 1, wherein the radiotherapy system is configured to control the electron beam (45) such that the X-ray beam delivers a radiation rate of less than 40 grays per second (Gy / s).

4. The radiotherapy system of claim 1, 2 or 3, wherein the first target (350-1) and the second target (350-2) are stacked in series.

5. The radiotherapy system of any one of the preceding claims, wherein the first target includes a plurality of slits (350- Id).

6. The radiotherapy system of any one of the preceding claims, wherein the first target is rectangular (350- la).

7. The radiotherapy system of any one of the preceding claims 1-4, wherein the first target is a wire(350-lb) or a plurality of wires.

8. The radiotherapy system of any one of the preceding claims 1-6, wherein the first target is a foil (350- la).

9. The radiotherapy system of any one of the preceding claims, wherein the first target includes brass.

10. The radiotherapy system of any one of the preceding claims, wherein the second target includes at least one of tantalum (Ta) or tungsten (W).

11. The radiotherapy system of claim 8, wherein the foil includes overlapping layers of the foil.

12. The radiotherapy system of claim 11, wherein the layers are triangular (450).

13. The radiotherapy system of any one of the preceding claims, wherein the thickness of the first target (350-1) is less than 1 cm.

14. The radiotherapy system of any one of the preceding claims, wherein the thickness of the first target (350-1) varies.

15. The radiotherapy system of any one of the preceding claims, further comprising:at least one cooling apparatus coupled to the second target and configured to supply a cooling fluid to the second target (350-2).

16. The radiotherapy system of any one of the preceding claims, wherein the X-ray target assembly is configured to absorb at least 99% of electrons of the electron beam, the electron beam incident on the first target (350-1).

17. The radiotherapy system of any one of the preceding claims, wherein the second target (350-2) is configured to absorb at least 90% of electrons of the dispersed electron beam.

18. An X-ray target assembly (50) configured to convert an electron beam (45) into an X-ray beam, the X-ray target assembly comprising:a first target (350-1) configured to disperse at least a portion of the electron beam (45); anda second target (350-2) configured to convert the portion of the electron beam (45) into the X-ray beam, a thickness of the second target (350-2) being greater than a thickness of the first target (350-1).

19. The X-ray target assembly of claim 18, wherein the first target (350-1) and the second target (350-2) are stacked in series.

20. The X-ray target assembly of claim 18 or 19, wherein the first target is a foil.

Images