Accelerator and particle beam therapy system

Abstract

As the ion beam is accelerated, the radius of the spiral orbit gradually increases, and the center of the spiral orbit moves in the predetermined radial direction of the gap toward the direction close to the peripheral portion, and then the moving direction of the spiral orbit is reversed and further moves toward the center of the gap. To achieve this, the intensity distribution in the orbit plane of the main magnetic field is designed. Thus, as a small accelerator capable of changing the energy of the extracted beam, the efficiency of beam injection from the external ion source into the accelerator is improved, and as a result, the dose rate of the extracted ion beam is improved.

Description

Technical Field

[0001] This invention relates to an accelerator and a particle beam therapy system for accelerating heavy ions such as protons or carbon ions, as well as a method for operating the accelerator. Background Technology

[0002] Accelerators are used to generate high-energy ion beams for applications such as particle beam therapy and physics experiments.

[0003] Particle beam therapy can be classified according to the type of particle beam used, including proton beam therapy that irradiates the affected area with proton beams and heavy particle beam therapy that irradiates the nuclei of atoms heavier than protons, such as carbon and helium. Proton beam therapy requires approximately 230 MeV of kinetic energy per nucleus, while carbon beam therapy requires approximately 430 MeV per nucleus. Several types of accelerators are known to generate these beams. For example, cyclotrons, synchrotrons, the synchrotron accelerator described in Patent Document 1, and the variable energy accelerator described in Patent Document 2 are known.

[0004] Cyclotrons and synchrotrons are characterized by accelerating a beam rotating in a static magnetic field using a high-frequency electric field. As the beam accelerates, its orbital radius of curvature increases, causing it to move outwards until it reaches its maximum energy and is then extracted. Therefore, the energy of the extracted beam is essentially fixed.

[0005] On the other hand, synchrotrons use the changing frequencies of the magnetic field of the electromagnets that deflect the beam and the high-frequency electric field that accelerates it to orbit the beam in a fixed path over time. Therefore, the beam can be extracted before reaching its designed maximum energy, and the extracted energy can be controlled.

[0006] In the synchrotron accelerator of Patent Document 1, a pair of ferromagnetic poles, each with a roughly circular cross-section of radius R, are aligned along their central axes and positioned vertically across a central plane. The pair of poles are separated by a gap, which forms a cavity with a profile substantially symmetrical with respect to the central plane. The height of the gap varies radially along the poles. The height of the gap is H along the central axis. center In the circular portion from the central axis to radius R2, as the radius increases, the distance from H... center It gradually increases, reaching its maximum value H at radius R2. max For the annular portion larger than radius R2, the height of the gap gradually decreases as the radius increases, and the gap height at the edge of the magnetic pole is H. edge Patent Document 1 discloses a synchrotron accelerator with a gap shape that can minimize the magnetic field within the gap and, on the other hand, minimize the size of the synchrotron accelerator.

[0007] On the other hand, in Patent Literature 2, a variable energy accelerator capable of emitting ion beams of different energies is disclosed. The accelerator is provided with an electromagnet in which a circular gap (space) is formed in the outer periphery. An ion source emits ion beams to predetermined positions near the outer periphery greatly deviated from the central axis of the circular gap to the radial direction. High frequency is irradiated to the incident ion beams, which are accelerated while rotating in the gap. Low-speed ion beams rotate in an orbit having a small radius, and the magnetic field distribution of the main magnetic field of the electromagnet is designed in such a manner that the center of the orbit gradually moves toward the central axis of the circular gap as the orbit radius increases.

[0008] At this time, in the accelerator of Patent Literature 2, the main magnetic field distribution of the electromagnet is designed in such a manner that the center of the orbit gradually moves toward the central axis of the circular gap as the orbit radius increases. Thus, as disclosed in Patent Literature 2 Figure 5 As disclosed, it is possible to make all orbits pass through a narrow region between the incident position of ions and the outer periphery of the gap. Therefore, by providing a magnetic field generating portion at the outermost periphery of the gap, it is possible to apply a force to the ions rotating around the orbit in a direction deviating from the orbit not only to the outermost periphery but also to one or more orbits inside the outermost periphery. Thus, it is possible to make the ion beams fluctuate in a direction away from the rotating orbit and enter an emission orbit outside the gap to be emitted outside the accelerator.

[0009] Thus, the accelerator of Patent Literature 2 can not only emit ion beams of the energy of the outermost periphery orbit but also emit ion beams of the energy of a plurality of orbits inside the outermost periphery, and thus can change the energy of the emitted ion beams.

[0010] Prior Art Documents

[0011] Patent Literature

[0012] Patent Literature 1: Japanese Patent Application Laid-Open No. 2013-541170

[0013] Patent Literature 2: Japanese Patent Application Laid-Open No. 2019-96405 SUMMARY

[0014] PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] The synchrotron accelerator described in Patent Literature 1 is an accelerator of a type in which a beam rotating in a main magnetic field is accelerated by a high-frequency electric field. In such a synchrotron accelerator, the rotating frequency of the beam decreases as the energy of the beam increases, and it is necessary to modulate the frequency of the high-frequency electric field in synchronization with the rotating frequency of the beam. Therefore, one operation cycle is constituted by the acceleration and extraction of a beam of low energy after the beam is incident, and further the re-incident of the beam. The operation cycle of the synchrotron accelerator is determined by the scanning speed of the resonance frequency of a cavity that excites the high-frequency electric field, and is generally several milliseconds or so. The total amount of the beam that rotates by one time in the operation cycle of several milliseconds is extracted. Also, the energy of the extracted beam is basically fixed.

[0016] In particle beam therapy, it is required to irradiate a beam to a tumor of an irradiation object not exceeding the allowable range of an irradiation dose decided in advance in a treatment plan or the like. In a synchrotron accelerator, the total amount of the beam is extracted in each operation cycle, and therefore in a particle beam therapy system using a synchrotron accelerator, it is necessary to set the amount of the beam that can be accelerated / extracted in one operation cycle of the synchrotron accelerator to be sufficiently small with respect to the allowable range of the irradiation dose. Therefore, there is a problem that the amount of electric charge accelerated in one operation cycle has to be made smaller than the upper limit determined by the performance of the accelerator, and the irradiation takes time to be completed.

[0017] Also, in the conventional synchrotron accelerator, in order to fix the rotating frequency of the beam independently of the energy, excitation of an isochronous magnetic field is required, and it is particularly difficult to excite the isochronous magnetic field to the energy region used in carbon beam therapy and accelerate the beam. Further, the synchrotron accelerator cannot change the energy of the extracted beam. On the other hand, although the synchrotron accelerator can change the energy of the extracted beam, there is a problem of large-scale in which the circumference of the orbit is 50 m or more.

[0018] On the other hand, the accelerator of Patent Literature 2 can not only emit an ion beam of the energy of the outermost circumference, but also can emit ion beams of the energy of one or more orbits inside the outermost circumference, but since the region in which the orbits are concentrated is formed in the outer peripheral portion of the gap, the position at which the ion beam is incident from the ion source becomes a position close to the outer periphery of the gap. As the accelerator of Patent Literature 2 Figure 2As shown, the ion source is mounted on the upper surface of the electromagnet, and a beam-incident through-hole 115 is provided at the magnetic pole of the electromagnet or the like, and the ion beam passes through the beam-incident through-hole 115 from the ion source to be incident into the gap. The beam-incident through-hole 115 is provided so as to pass through a position near the outer periphery of the gap, i.e., a position near the outer periphery of the magnetic pole, and is arranged so as to cross the magnetic lines of force passing through the magnetic pole. Therefore, the ion beam traveling inside the beam-incident through-hole 115 is subjected to the magnetic field of the magnetic lines of force inside the magnetic pole, and a Lorentz force is generated to cause a drift motion. In order to avoid this, for example, a structure is required in which a pair of electrodes is arranged near the beam-incident through-hole 115, an electric field is applied to the ion beam, the Lorentz force is balanced with the force received from the electric field, and the ion beam is caused to travel straight inside the beam-incident through-hole 115, or the like. Therefore, in the accelerator of Patent Document 2, the efficiency of the ion beam incident into the gap from the ion source is affected by the magnitude of the voltage that can be applied to the ion-incident through-hole.

[0019] An object of the present application is to improve the efficiency of the beam incident into an accelerator from an external ion source in a small accelerator in which the energy of the extracted beam can be changed, and as a result, to improve the dose rate of the extracted ion beam.

[0020] Means for solving the problem

[0021] In order to achieve the above object, the accelerator of the present application has: an electromagnet including a pair of magnetic poles facing each other across an orbit surface on which an ion beam rotates, and forming a main magnetic field that generates a plurality of rotation orbits on the orbit surface; an ion-incident through-hole formed in the magnetic pole in order to introduce an ion beam from the outside to a predetermined incident position of the orbit surface; a high-frequency acceleration cavity inserted into a gap formed between the pair of magnetic poles, and generating a high frequency for accelerating the ion beam rotating around the orbit surface; and an additional magnetic field generating portion and an extraction passage, the additional magnetic field generating portion being arranged at the outer periphery of the gap, and applying a magnetic field to the ion beam moving on the outermost periphery and one or more rotation orbits inside the outermost periphery to deviate the moving direction from the rotation orbit, and the extraction passage guiding the ion beam deviated from the rotation orbit outside the gap. The intensity distribution in the orbit surface of the main magnetic field is designed so that as the ion beam is accelerated, the radius of the rotation orbit gradually increases, and the center thereof moves in the predetermined radial direction of the gap toward the direction close to the peripheral portion, and then the moving direction is reversed to further move toward the center of the gap.

[0022] Effect of the Invention

[0023] According to the present application, it is possible to increase the beam irradiation amount from a small accelerator in which the energy of the extracted beam can be changed, and to achieve an improvement in the dose rate in a particle beam therapy system. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1is a perspective view showing the overall outline shape of an accelerator of the first embodiment of the present application.

[0025] Figure 2 is a longitudinal sectional view of the accelerator of the first embodiment.

[0026] Figure 3 is a transverse sectional view of the accelerator of the first embodiment.

[0027] Figure 4 is a view showing the rotational orbit of a beam and the isorotational phase line in the accelerator of the first embodiment of the present application.

[0028] Figure 5 is a view showing a representative rotational orbit and the moving direction of the center thereof in the accelerator of the first embodiment of the present application.

[0029] Figure 6 is a control block diagram of the accelerator of the first embodiment of the present application.

[0030] Figure 7 is a view showing the beam rotational orbit energy dependence of the main magnetic field strength in the accelerator of the first embodiment of the present application.

[0031] Figure 8 is a view showing the beam rotational orbit energy dependence of the rotational frequency of a beam in the accelerator of the first embodiment of the present application.

[0032] Figure 9 is a timing chart of the operation in the accelerator of the first embodiment of the present application.

[0033] Figure 10 is a flowchart of the operation control in the accelerator of the first embodiment of the present application.

[0034] Figure 11 is a structural view of a particle beam therapy system of the second embodiment of the present application.

[0035] Figure 12 is a longitudinal sectional view of the accelerator of the comparative example.

[0036] Figure 13 is a view showing the rotational orbit of a beam and the isorotational phase line in the accelerator of the comparative example.

[0037] Figure 14 is a view showing a representative rotational orbit and the moving direction of the center thereof in the accelerator of the comparative example. DETAILED DESCRIPTION

[0038] Hereinafter, an embodiment of an accelerator and a particle beam therapy system of the present application will be described using the accompanying drawings.

[0039] First Embodiment

[0040] As a first embodiment, an accelerator 1 of a particle beam therapy system is described below using the drawings.

[0041] <Summary>

[0042] First, a summary of the accelerator 1 is described. The appearance of the accelerator 1 is shown in Figure 1 , a longitudinal sectional view thereof is shown in Figure 2 , and a cross-sectional view is shown in Figure 3 . In addition, in Figure 3 , hatching is applied to portions other than cross sections in order to easily understand the internal structure. Figure 4 A rotational orbit of the accelerator 1 and an iso-rotational phase line are shown in Figure 5 , and a movement of a center of a representative rotational orbit is shown in Figure 6 , and a control system of the accelerator is shown in Figure 7 , and a main magnetic field strength of each energy of the rotational orbit is shown in

[0043] The accelerator of the present embodiment is, for example, a frequency modulation type variable energy accelerator that accelerates carbon ions to a maximum of 435 MeV / u.

[0044] As shown in Figures 1 to 3 , the accelerator includes an electromagnet 11. The electromagnet 11 has a pair of magnetic poles 123a, 123b that oppose each other across an orbit face 20a that rotates the ion beam. Thereby, a main magnetic field that forms a plurality of rotational orbits Figure 4 , Figure 5 of the orbit face 20a is formed.

[0045] As shown in Figure 1 and Figure 2 , a beam-incident through-hole 115 is formed in the magnetic poles 123a, 123b. The beam-incident through-hole 115 introduces the ion beam 25 from the outside to a predetermined incident position 130 of the orbit face 20a.

[0046] As shown in Figure 2 and Figure 3 , a cavity 11a of a predetermined shape is formed between the pair of magnetic poles 123a, 123b in a manner that sandwiches the orbit face 20a, and a high-frequency acceleration cavity 21 is inserted in the cavity 11a. The high-frequency acceleration cavity 21 generates high frequencies that accelerate the ion beam that rotates in the orbit face 20a.

[0047] An additional magnetic field generating unit (coil for generating additional magnetic field) is arranged on the outer periphery of the gap 11a. This additional magnetic field generating unit applies a magnetic field to the ion beam on the outermost periphery and one or more rotating tracks closer to the inner periphery, causing them to deviate from the rotating tracks. Furthermore, an extraction channel 312 that guides the ion beam deviating from the rotating tracks to the outside of the gap 11a is arranged on the outer periphery of the gap 11a.

[0048] At this point, the intensity distribution within the orbital plane of the main magnetic field generated by electromagnet 11 is designed as a rotating orbit (representative rotating orbits O1 to O12). Figure 4 , Figure 5 That configuration. That is, the distribution of the main magnetic field strength is designed to be such that, based on the energy of the rotating orbit... Figure 7 The larger magnetic field (B) shown is applied to the location of the rotating orbit.

[0049] Specifically, Figure 4 , Figure 5 The rotating orbit shown changes as the ion beam accelerates (e.g., the rotating orbit...). Figure 5 The radii of the rotation tracks (O1 to O12) gradually increase, and their centers (C1 to C12), after moving towards the periphery along the predetermined radial direction Rp of the gap 11a, reverse their direction of movement and move further towards the center of the gap 11a. More specifically, the centers (C1 to C4) of the rotation tracks (O1 to O4) that reach a predetermined first radius move sequentially towards the periphery of the gap 11a, and the centers (C5 to C12) of the rotation tracks (O5 to O12) that reach the first radius move sequentially towards the center 20c of the track surface 20a.

[0050] Thus, by designing the rotational track (e.g., O1-O4) to temporarily move towards the periphery 20b of the track surface 20a from its center (C1-C4), the rotational track (e.g., O5-O12) moves towards the center 20c of the track surface 20a, and the distance between the incident position 130 and the periphery 20b of the track surface 20a ( Figure 4 , Figure 5 Wider than the comparative example (see reference) Figures 12 to 14 It is a structure that moves the center position of the rotating track in one direction, like an accelerator.

[0051] In other words, the incident position 130 of the ion beam can be configured to be close to the center 20c of the gap 11a, and the through hole 115 for beam incident can also be configured to be close to the central axis 20e of the magnetic pole 123a.

[0052] like Figure 2As shown, in the region close to the central axis 20e of the magnetic pole 123a, the magnetic lines of force 90 within the magnetic pole 123a are inclined with respect to the central axis of the through-hole 115 for beam incidence. Therefore, by configuring the through-hole 115 for beam incidence close to the central axis 20e of the magnetic pole 123a, the magnetic field component orthogonal to the traveling direction (central axis) of the ion beam 25 can be reduced compared to the comparative example. Figure 12 The magnetic field component orthogonal to the traveling direction (central axis) of the ion beam 25 can be reduced compared to the comparative example.

[0053] Thus, in the accelerator 1 of the present embodiment, the magnetic field component orthogonal to the traveling direction (central axis) of the ion beam 25 can be reduced compared to the comparative example. Figure 12 The Lorentz force received by the ion beam 25 from the magnetic field 90a within the through-hole 115 for beam incidence can be reduced, and the electric field applied to the ion beam 25 for canceling the Lorentz force can be reduced compared to the comparative example. Therefore, an electric field sufficient to make the ion beam 25 travel straight can be easily applied, the incidence efficiency of the ion beam 25 to the incidence position 130 can be improved, and as a result, the dose rate of the ion beam emitted from the accelerator can be improved.

[0054] On the other hand, by being designed to temporarily move the center (C1 to C4) of the rotation track (e.g., O1 to O4) toward the direction of the peripheral portion 20b close to the track surface 20a, and then reverse the moving direction to move the center (C5 to C12) of the rotation track (e.g., O5 to O12) toward the center 20c of the track surface 20a, a concentration region 241 through which the rotation tracks densely pass can be formed near the peripheral portion 20b of the track surface 20a as in the comparative example (C) even though the distance from the incidence position 130 to the peripheral portion 20b of the track surface 20a is wider than the comparative example. Figures 12 to 14 ) same as the comparative example (C).

[0055] Therefore, by applying a magnetic field to the concentration region 241 from the additional magnetic field generating gasket 311 arranged on the outer periphery of the gap 11a, the moving direction of the ion beam in the movement on the outermost periphery and one or more rotation tracks inward of the outermost periphery can be deviated from the rotation track, and extracted to the outside of the gap 11a from the extraction passage 312.

[0056] In addition, it is preferable that the distance between the central axis of the through-hole 115 for beam incidence and the center of the gap 11a be set within 50% of the length of the radius of the gap 11a.

[0057] It can also be configured that a gasket 250 such as an iron sheet is arranged on the magnetic pole surface 124a at a position between the through-hole 115 for beam incidence and the center of the magnetic pole 123a and adjacent to the through-hole 115 for beam incidence. Thus, the magnetic field gradient of the region where the gasket 250 is arranged becomes large, and therefore the magnetic field component orthogonal to the traveling direction (central axis) of the ion beam 25 can be reduced compared to the comparative example. Figure 4 and Figure 5As shown, the center (C1 to C4) of the rotation orbit (O1 to O4) can be moved in a direction approaching the outer periphery of the gap 11a. In particular, the magnetic field gradient at each position along the radial direction Rp between the beam-incident through-hole 115 and the center of the magnetic pole 123a is preferably configured to have the maximum magnetic field gradient at the position where the spacer 250 is provided.

[0058] The beam-incident through-hole 115 and the spacer 250 are preferably provided at positions symmetrical with the opposed magnetic poles 123a, 123b across the orbit face 20a.

[0059] In addition, the distance between a pair of spacers 250 is preferably narrower than the distance between a pair of magnetic pole faces 124a, 124b at a position along the predetermined radial direction between the beam-incident through-hole 115 and the outer periphery of the magnetic pole face 124a and a position 251 adjacent to the ion-incident through-hole, or the distance of the spacers provided at the position 124a, 124b.

[0060] The magnetic field gradient at each position along the radial direction between the beam-incident through-hole 115 and the outer periphery of the gap 11a is preferably the maximum at the collection region 241 of the peripheral portion of the gap 11a. Thus, as shown in Figure 4 and Figure 5 As shown, the rotation orbit can be densely configured at the collection region 241 of the peripheral portion of the gap 11a.

[0061] An ion source 12 that emits an ion beam to the beam-incident through-hole 115 is provided outside the electromagnet 11.

[0062] The extraction passage 312 is preferably provided at a predetermined radial direction Rp outer periphery portion of the gap 11a.

[0063] A plurality of annular trim coils 33 are preferably provided at the magnetic pole faces 124a, 124b. The trim coils 33 have radii corresponding to the plurality of rotation orbits of the orbit face 20a, and are provided at the magnetic pole faces 124a, 124b at positions corresponding to the rotation orbits.

[0064] The high-frequency acceleration cavity 21 includes a D-shaped electrode 221. The edge of the D-shaped electrode 221 is configured to cross the gap 11a in parallel with the orbit face 20a. The shape of the D-shaped electrode 221 is a W-letter shape centered on the incident position 130.

[0065] Hereinafter, the accelerator 1 of the present embodiment will be described in detail.

[0066] <<Structure of Accelerator 1>>

[0067] As shown in Figure 1 The accelerator 1 has an electromagnet 11 that can be divided into upper and lower portions with the division face 12a as a boundary. As shown inFigure 2 As shown in the figure, the electromagnet 11 is provided with: cylindrical upper and lower magnetic poles 123a and 123b that are opposed across the split connecting surface 12a; cylindrical side yokes 121a and 121b that are respectively arranged on the outer periphery of the upper and lower magnetic poles 123a and 123b; and disc-shaped upper and lower top plates 122a and 122b. The disc-shaped upper top plate 122a is arranged so as to cover and join the upper end surface of the upper magnetic pole 123a and the upper end surface of the side yoke 121a. Similarly, the lower top plate 122b is arranged so as to cover and join the lower end surface of the lower magnetic pole 123b and the lower end surface of the side yoke 121b. In this embodiment, the magnetic pole 123a, the side yoke 121a, and the top plate 122a, and the magnetic pole 123b, the side yoke 121b, and the top plate 122b are formed integrally. In the recesses formed between the magnetic pole 123a and the side yoke 121a, and between the magnetic pole 123b and the side yoke 121b, respectively, there are arranged annular coils 13. The coils 13 are wound along the outer peripheral wall of the magnetic pole 123.

[0068] The mutually opposed surfaces of the upper and lower magnetic poles 123a and 123b of the electromagnet 11 are defined as magnetic pole surfaces 124a and 124b. In the gap 11a sandwiched by the magnetic pole surfaces 124a and 124b, a main magnetic field 110 is formed in the up-down direction by the flow of current in the coils 13. The magnetic pole surfaces 124a and 124b are concave curved surfaces that are symmetrical across the split connecting surface 12a, and the distance between the magnetic pole surfaces 124a and 124b is greatest at the center axis 20e of the magnetic poles 123a and 123b, and decreases as it approaches the end portions.

[0069] The surface within the gap 11a that is equidistant from the magnetic pole surfaces 124a and 124b is the trajectory surface 20a of the beam, and the disc-shaped region of a predetermined thickness centered on the trajectory surface 20a is the beam passing region 20. The beam passing region 20 is the region within the gap 11a through which the beam passes during acceleration / rotation.

[0070] The intensity distribution of the magnetic field formed in the beam passing region 20 is designed so as to be a gradient according to the energy of the rotational orbit at its position. The gradient of the magnetic field is described in detail later. In addition, the gap 11a of the electromagnet 11 is evacuated by a vacuum pump, which is not shown.

[0071] A plurality of through holes that connect the outside to the beam passing region 20 are provided in the electromagnet 11. Specifically, various through holes, such as a through hole 111 for extracting the accelerated beam, a through hole 112 for leading the coil conductor arranged inside the electromagnet 11 to the outside, a high-frequency power input through hole 114, and the like, are provided on the surface of the upper and lower split connecting surfaces 11b.

[0072] A high-frequency accelerating cavity (accelerating electrode) 21 is inserted into the electromagnet 11 through a high-frequency power input through-hole 114. The high-frequency accelerating cavity 21 forms an accelerating electric field E for accelerating ions within the gap 11a to form an ion beam. As described later, the high-frequency accelerating cavity 21 includes a D-shaped electrode 221 for acceleration (see reference). Figure 3 ) and a rotary variable capacitance capacitor (modulation unit) 212 for modulating the frequency of the electric field used for acceleration.

[0073] like Figure 1 As shown, an ion source 12 for supplying ions (e.g., carbon ions) is provided at a position off-center from the central axis 20e on the upper surface of the electromagnet 11. Furthermore, at the mounting position of the ion source 12, a beam-injection through-hole 115 is provided in the top plate 122a and the magnetic pole 123a (see reference). Figure 1 The ion beam 25 emitted from the ion source 12 passes through the beam incident through-hole 115 and enters the gap 11a from the incident position 130.

[0074] At this time, the magnetic field lines 90 generated by coil 13 and passing through magnetic pole 123a, yoke 121a and top plate 122a to draw a closed loop are as follows: Figure 2 The beam passes through the through-hole 115 as shown. The ions emitted from the ion source 12 have an energy of about 100 keV. Therefore, the magnetic field 90a on the path from the ion source 12 to the incident position 130 within the through-hole 115 is deflected by the Lorentz force and drifts around the magnetic field lines 90.

[0075] To apply a force to the ions to counteract the Lorentz force, a pair of electrodes 91 are arranged near the beam entrance aperture 115, separated from it. The pair of electrodes 91 apply an electric field to the ion beam 25, generating a force that balances the Lorentz force experienced by the ion beam 25 from the magnetic field 90a. The direction of the electric field applied by the electrodes 91 is... Figure 2 The direction of arrow 91a. Additionally, in Figure 2 The diagram only shows one of the pair of electrodes 91. Electricity applied to the pair of electrodes 91 is supplied externally through a beam entrance aperture 115. The ion beam 25 traveling within the beam entrance aperture 115 is balanced by the force exerted by the electric field generated by the pair of electrodes 91 and the Lorentz force exerted by the magnetic field 90a, thus traveling straight within the beam entrance aperture 115 and reaching the incident position 130 within the gap 11a.

[0076] Further, although not shown, a deflector is arranged near the incident position 130 of the beam-incident through-hole 115, and the traveling direction of the ion beam 25 that travels in the beam-incident through-hole 115 and reaches the incident position 130 from a direction perpendicular to the orbit surface 20a is deflected to a direction parallel to the orbit surface 20a. Thus, the ions are rotated around the orbit surface 20a.

[0077] The portion of the high-frequency acceleration cavity 21 inserted into the electromagnet 11, particularly the portion fixedly arranged in the gap 11a, is defined as a D-shaped electrode 221. The D-shaped electrode 221 is a pair of plate-shaped electrodes covering a portion of the beam-passing region 20 from above and below. As shown in Figure 3 The edge 221a of the D-shaped electrode 221 that crosses the beam-passing region 20 in the in-plane direction is shaped in a W-letter shape as a vertex near the incident position 130. The peripheral edge portion of the D-shaped electrode 221 encloses the outermost peripheral orbit and is in a circular arc shape along the outer periphery of the gap 11a. The portion of the high-frequency acceleration cavity 21 other than the D-shaped electrode 22 penetrates the high-frequency power input through-hole 114 from the circular arc-shaped peripheral edge portion of the D-shaped electrode 22 and is led to the outside of the electromagnet 11.

[0078] As shown in Figure 1 A rotary variable-capacitance capacitor (modulation portion) 212 is attached to the high-frequency acceleration cavity 21 led to the outside of the electromagnet 11. The rotary variable-capacitance capacitor 212 has a rotary shaft 213 on which a servo motor 214 is connected (see Figure 6 ). The servo motor 214 drives the rotary shaft 213 to rotate, and the rotation angle of the rotary shaft 213 changes with time, whereby the electrostatic capacitance of the high-frequency acceleration cavity 21 is modulated and the resonance frequency of the fundamental mode of the high-frequency acceleration cavity 21 changes. Thus, the frequency of the acceleration high-frequency electric field generated by the high-frequency acceleration cavity 21 can be changed. Further, the high-frequency acceleration cavity 21 is provided with an input coupler 211 for inputting high-frequency electric power.

[0079] A W-letter-shaped linear ground electrode 222 is arranged in opposition to the end surface of the W-letter-shaped edge 221a of the D-shaped electrode 221 at a predetermined interval therefrom. The region sandwiched by the D-shaped electrode 221 and the ground electrode 222 is an acceleration gap 223.

[0080] The high-frequency acceleration cavity 21 excites an acceleration high-frequency electric field for accelerating ions by a λ / 4-type resonance mode in the acceleration gap 223. The ions incident from the incident position 130 are accelerated by the high-frequency electric field excited by the acceleration gap 223 while rotating in the orbit surface 20a of the beam-passing region 20 and passing near the acceleration gap 223.

[0081] To synchronize with the rotation frequency of the beam, the frequency of the high-frequency electric field excited by the high-frequency accelerating cavity 21 in the accelerating gap 223 is set to an integer multiple of the beam's rotation frequency. Specifically, this is achieved through the motor control device 41 (see reference). Figure 6 The servo motor 214 is controlled to adjust the rotation speed of the rotating shaft 213. In the accelerator 1 of this embodiment, the control is performed in the acceleration gap 223 such that the frequency of the high-frequency electric field is 1 times the rotation frequency of the beam.

[0082] To fine-tune the distribution of the main magnetic field 110 on the orbital plane 20a, multiple annular fine-tuning coils 33 are provided on the magnetic pole surfaces 124a and 124b of the magnetic poles 123a and 123b. The fine-tuning coils 33 are positioned on the magnetic pole surfaces 124a and 124b at positions corresponding to the rotational orbits of the orbital plane 20a, with radii corresponding to the multiple rotating orbits. For example, the center of the fine-tuning coil 33 with the largest diameter is aligned with the center 20c of the electromagnet 11. On the other hand, the center of the fine-tuning coil 33 with the smallest diameter is aligned with the incident position 130. That is, regarding the center of the fine-tuning coil 33, the center with the smaller diameter is off-center relative to the centers of the magnetic poles 123a and 123b. The diameter and center position of the fine-tuning coil 33 correspond to the diameter and center position of the ion beam's orbit.

[0083] The fine-tuning coil 33 is connected to an external power source through the through-hole 112, and the excitation current supplied to the fine-tuning coil 33 of each system is adjusted separately before operation. As a result, the magnetic field from the fine-tuning coil 33 is superimposed on the main magnetic field 110 applied from the magnetic poles 123a and 123b to the track surface 20a, making the distribution of the main magnetic field 110 on the track surface 20a close to the desired distribution. This enables stable electron induction accelerator oscillation and allows the center of the ion's orbit to move in the desired direction as the ion beam accelerates. The direction of movement of the ion's orbital center will be explained in detail later.

[0084] In addition, such as Figure 2 and Figure 3 As shown, in order to extract the beam accelerated within the accelerator 1, a pair of additional magnetic field generating pads (kick portions) 311 for energizing a quadrupole magnetic field or a multi-pole magnetic field with six or more poles are provided on a portion of the magnetic pole surfaces 124a and 124b in an electrically insulated state relative to the magnetic pole surfaces 124a and 124b, and interference electrodes (interference portions) 313 for applying a high-frequency electric field to interfere with the beam. Additionally, an entrance portion for an extraction channel 312 is provided at one end of the magnetic pole surface 124.

[0085] Interference electrode 313 applies a small-amplitude high-frequency (RF) electric field as an interference high-frequency electric field to the beam, increasing the amplitude of the electron-induced accelerator vibration of the particles in the rotating beam and causing them to pass through the area affected by the jump magnetic field excited by the additional magnetic field generating pad 311. The jump magnetic field of the additional magnetic field generating pad 311 causes the particles to jump out of the designed track, causing the beam to detach from the designed track. The beam reaches the area of ​​the main magnetic field 110 formed by the shielded extraction channel 312, passes through the extraction track 322, and is extracted to the outside through the extraction beam through hole 111 of the accelerator 1. The jump magnetic field excited by the additional magnetic field generating pad 311 restricts the ion beam rotating in the beam passing area 20 to a stable region, and guides particles appearing outside the stable region into the extraction channel 312. In the accelerator 1 of this embodiment, the additional magnetic field generating pad 311 is a pair, which is a structure that superimposes magnetic fields of opposite polarities on the main magnetic field 110 formed by the magnetic poles 123.

[0086] Thus, by opening / closing the high-frequency electric field generated by the interference electrode 313, the beam extraction can be controlled to open / close synchronously. Details regarding the operation of the interference electrode 313, the extraction channel 312, and the additional magnetic field generating pad 311 will be described later.

[0087] In accelerator 1, the shapes and arrangements of the upper and lower magnetic poles 123a and 123b, coil 13, fine-tuning coil 33, auxiliary magnetic field generating pad 311, extraction channel 312, and interference electrode 313 are designed such that the in-plane component of the main magnetic field 110 on the orbital plane is approximately zero, resulting in a plane-symmetrical configuration / current distribution relative to the orbital plane 20a. Additionally, as... Figure 3 As shown, when the accelerator 1 is viewed from the top surface, the shapes of the magnetic pole 123, D-shaped electrode 221, coil 13, fine-tuning coil 33, and interference electrode 313 are symmetrical about the left and right with respect to the line segment 11c that connects the center of the through hole 114 to the center of the through hole 112.

[0088] use Figure 6The structure of the control section of the accelerator 1 will be described. A servo motor 214 that rotates the rotary variable capacity capacitor 212 is connected to the rotary shaft 213 of the rotary variable capacity capacitor 212 of the high frequency acceleration cavity 21. A motor control device 41 is connected to the servo motor 214. Further, a low level high frequency generating device 42 that generates high frequency power and an amplifier 43 are connected to the input coupler 211 of the high frequency acceleration cavity 21. Furthermore, a high frequency power source 46 is connected to the interference electrode 313, and an interference high frequency control device 47 to be controlled is connected to the high frequency power source 46. The low level high frequency generating device, the motor control device 41, and the interference high frequency control device 47 are connected to an overall control device 40 that controls them.

[0089] In the present embodiment, a voltage amplitude calculating device 45 and a treatment planning database 60 are connected to the overall control device 40. In the treatment planning database 60, a plurality of irradiation positions, and the energy and dose of the particle beam that should be irradiated for each irradiation position are stored. The overall control device 40 controls the output of the low level high frequency generating device 42 to excite a high frequency electric field of a predetermined amplitude in the acceleration gap 223.

[0090] Next, the operation of each section when the ions are accelerated by the accelerator 1 of the present embodiment and the ion beam (particle beam) of the desired energy is emitted will be described.

[0091] <Beam entry into the accelerator 1>

[0092] In the accelerator 1, the ions from the ion source 12 are incident into the beam entry through hole 115. The ions perform a drift motion due to the Lorentz force from the magnetic field 90a of the magnetic field lines 90 that cross the beam entry through hole 115, but are given an appropriate kick by the electric field applied by the electrode 91, and thus reach the vicinity of the entry position 130 from a direction substantially perpendicular to the orbital plane 20a, and in the vicinity of the orbital plane 20a, the direction of motion of the beam is deflected by a deflector (not shown) to be parallel to the orbital plane 20a.

[0093] That is, it is necessary to set the magnitude of the electric field in such a manner that the force on the ion beam from the magnetic field and the force from the electric field are balanced within the beam entry through hole 115. Therefore, the smaller the magnetic field perpendicular to the direction of motion of the beam, that is, the magnetic field parallel to the orbital plane 20a, the smaller the electric field required, and the control of the beam trajectory and size becomes easy, and an improvement in the entry efficiency can be achieved.

[0094] Therefore, in the present accelerator 1, the entry position 130 is disposed so as to be closer to the magnetic field than the entry position 130 of the conventional accelerator 1. Figure 12The variable energy accelerator in the comparative example (existing construction) shown is closer to the center 20c of the magnetic poles 123a and 123b. Therefore, the transverse magnetic field applied to the incident beam path of the beam-entry through-hole 115 extending directly above it can be sufficiently reduced to a size controllable by the electric field. As a result, compared to the conventional ( Figure 12 Compared to variable energy accelerators, the increased incident beam volume allows for an increase in the amount of charge that can be accelerated and irradiated in one operating cycle.

[0095] On the other hand, the incident position 130 is close to the center of the magnetic poles 123a and 123b, thus increasing the distance between the incident position 130 and the outer periphery of the gap 11a. Therefore, in order to reduce the distance between the orbits of the collection region 241 of the periphery from which the ion beam is extracted, the distance between the orbits is reduced to that of the comparative example ( Figure 12 The rotating track of the accelerator ( Figure 13 To the same extent, in this embodiment, such as Figure 4 and Figure 5 As shown, as the radius of the rotating track increases from the minimum track size, the center of the track temporarily moves towards the periphery of the gap 11a (track surface 20a). Then, as the track radius further increases, the center of the track moves towards the center 20c of the gap 11a (track surface 20a).

[0096] Beam Acceleration and Removal within Accelerator 1

[0097] Next, the trajectory and motion of the beam rotating in this accelerator 1 will be described.

[0098] The beam is accelerated each time it passes through the acceleration gap 223 while rotating around the incident position 130 in the beam-passing region 20. As an example, the minimum kinetic energy of the extractable beam in the accelerator 1 of this embodiment is 140 MeV / µm, and the maximum is 430 MeV / µm. The greater the kinetic energy, the lower the beam rotation frequency. In the kinetic energy beam immediately after incident, a beam reaching 35 MHz and 430 MeV rotates at 22 MHz in the beam-passing region 20. The relationship between these energies and rotation frequency is as follows... Figure 8 As shown.

[0099] In accelerator 1, the main magnetic field 110 formed by electromagnet 11 and fine-tuning coil 33 is uniform along the trajectory of the beam, and the magnetic field decreases as the energy increases (see reference). Figure 7 The distribution of the magnetic field. That is, the magnetic field that is reduced in the radial direction.

[0100] Under such a magnetic field, particles that deviate slightly radially from the designed trajectory experience a restoring force similar to that required to return to the designed trajectory. Simultaneously, particles deviating vertically relative to the trajectory plane also experience a restoring force from the main magnetic field 110 in the direction of returning to the trajectory plane. That is, if the magnetic field is appropriately reduced relative to the beam energy, a restoring force always acts from the particles deviating from the designed trajectory in the direction they wish to return to the designed trajectory, causing them to oscillate near the designed trajectory (electron induction accelerator oscillation). Thus, the beam can be stably rotated / accelerated by the main magnetic field. The values ​​of the main magnetic field 110 in beams of various energies are shown in... Figure 7 The main magnetic field 110 is at its maximum of 4.63T at the incident position 130, and decreases to 4.45T at the outermost periphery.

[0101] The aforementioned main magnetic field 110 distribution is achieved by passing a predetermined excitation current through the coil 13 of the electromagnet 11 and the auxiliary fine-tuning coil 33, magnetizing the magnetic poles 123a and 123b, which are excited as a superposition of the magnetic field from the coil 13 and the magnetic field from the magnetic poles 123a and 123b. To form a distribution that increases the magnetic field at the ion incident position 130 and decreases towards the outer periphery, the shapes of the magnetic pole surfaces 124a and 124b and the pad 250 are determined such that the relative distance between the magnetic pole surfaces 124a and 124b (the height of the gap 11a) is greatest at the center of the gap 11a and decreases towards the outer periphery. Furthermore, the shape of the magnetic pole surface 124 is symmetrical with respect to the plane (track surface) passing through the center of the gap, and has only a magnetic field component perpendicular to the track surface on the track surface. Furthermore, by adjusting the current applied to the fine-tuning coil 33 located on the magnetic pole surface, the magnetic field distribution is finely adjusted, thereby exciting the predetermined main magnetic field 110 distribution.

[0102] The orbits of each energy are as follows Figure 4 As shown. Figure 4 As shown, the outermost rotating orbit contains a circular orbit with a radius of 1.5m corresponding to the orbit with the maximum energy of 435MeV. From this point to 0MeV, there are a total of 51 circular orbits divided into 51 sections based on magnetic stiffness. The dashed lines are lines connecting the same rotational phase of each orbit, called the iso-rotational phase lines.

[0103] like Figure 5 As shown, in the accelerator 1 of this embodiment, as the beam accelerates, the beam's orbital center (designed orbit) moves in one direction (radial direction Rp) within the orbital plane. Figure 4 The beam moves while changing its orientation in the Y direction (where X=0). The design trajectory movement results in areas where different kinetic energies converge (converging regions 240, 241) and areas that move away from each other (discrete regions 242, 243). In other words, the beam's designed trajectory is eccentric.

[0104] In accelerator 1, there are two convergence regions 240 and 241 where the design trajectories converge. In either convergence region 240 or 241, the line segment connecting the points of the design trajectories closest to each other (convergence points) is orthogonal to all design trajectories. Conversely, in two discrete regions 242 and 243, the line segment connecting the points of the design trajectories furthest from each other is orthogonal to all design trajectories. These two line segments exist on the same straight line. Figure 4 In the Y direction where X=0: the radial direction Rp). If this line is defined as the axis of symmetry, then the shape of the designed track is symmetrical with respect to the plane passing through the axis of symmetry and perpendicular to the track plane.

[0105] In the convergence regions 240 and 241, the spatial gradient of the magnetic field becomes steeper compared to the surrounding area. Therefore, a predetermined magnetic field distribution is formed by placing iron pads 250, etc., on the magnetic poles 123a and 123b. In particular, in this accelerator 1, the magnetic field gradient is maximized at the convergence point on the low-energy side. Therefore, as... Figure 2 As shown, a gasket 250 is disposed at the edge of the through-hole 115 for beam incidence. Furthermore, in Figure 2 The illustration of the gaskets configured in the collection area 241 is omitted.

[0106] Figure 4 The iso-rotational phase lines shown are drawn from the convergence region at π / 20 for each rotational phase. The acceleration gap 223 formed between the D-shaped electrode 221 and the ground electrode 222 opposite to the D-shaped electrode 221 is positioned along an iso-rotational phase line 244 rotated ±90 degrees from the convergence point. The iso-rotational phase line 244 is as follows... Figure 4 The figure shows a W-shape centered at the incident position 130. Therefore, the edge 221a of the D-shaped electrode 221 and the ground electrode 222 are opposite each other across the equal rotation phase line 244 and are W-shaped along the shape of the equal rotation phase line 244.

[0107] As described above, the high-frequency accelerating cavity 21 generates a high-frequency electric field in the accelerating gap 223. As described above, as... Figure 6 As shown, in the high-frequency accelerating cavity 21, through the input coupler 211 (refer to...) Figure 1) is connected with a low-level high-frequency generating device 42 and an amplifier 43. In the high-frequency acceleration cavity 21, high-frequency electric power generated by the low-level high-frequency generating device 42 and amplified by the amplifier 43 is introduced, whereby a high-frequency electric field is excited in the acceleration gap 223 between the D-shaped electrode 221 and the grounded electrode 222 of the high-frequency acceleration cavity 21. Normally, the electromagnetic field excited by the D-shaped electrode 221 is an electromagnetic field of a specific resonance frequency and a spatial distribution determined by the electrode shape and the electrostatic capacity of the rotary variable capacity capacitor 212. In this case, when the beam passes through the acceleration gap, the electric field is generated in the same direction from the D-shaped electrode 221 with respect to the grounded electrode 222 at a certain time at each place in the acceleration gap 223, and the electric field is generated in the opposite direction from the previous direction when the beam passes through the acceleration gap on the opposite side after passing through half a cycle. As a result, it is possible to apply a force from the electric field to the direction in which the beam is to be accelerated when the beam passes through the acceleration gap 223, and to increase the beam energy while rotating.

[0108] In the accelerator 1 of the present application, the high-frequency electric field is excited in synchronization with the rotation of the beam, and therefore the frequency of the electric field is modulated as in a graph like Figure 8 corresponding to the energy of the beam in rotation, and the beam is gradually accelerated to a desired energy Figure 8 In the high-frequency acceleration cavity 21 using a resonance mode, it is necessary to scan the frequency of the high frequency in a range wider than the amplitude of resonance. Therefore, it is also necessary to change the resonance frequency of the high-frequency acceleration cavity 21. This control is performed by changing the electrostatic capacity of the rotary variable capacity capacitor 212 provided at the end of the high-frequency acceleration cavity 21. A conductor plate is connected to the rotation shaft 213 of the rotary variable capacity capacitor 212, and by rotating the rotation shaft 213, it is possible to control the electrostatic capacity generated between the conductor plate and the external conductor by the rotation angle of the rotation shaft 213. That is, by changing the rotation angle of the rotation shaft 213 as the beam is accelerated, it is possible to change the resonance frequency of the high-frequency acceleration cavity 21.

[0109] Next, the behavior of the beam from the time when the beam of the accelerator 1 of the present embodiment is injected until it is extracted will be further described.

[0110] First, ions of low energy are output from the ion source 12, and the beam is guided to the beam passing region 20 via the beam injection through-hole 115 and the injection position 130.

[0111] When the ions from the ion source 12 are injected into the beam injection through-hole 115, the ions perform a drift motion due to the Lorentz force from the magnetic field 90a of the magnetic field line 90 that crosses the beam injection through-hole 115, but are appropriately kicked by the electric field applied by the electrode 91, whereby they reach the vicinity of the injection position 130 from a direction substantially perpendicular to the orbital plane 20a, and in the vicinity of the orbital plane 20a, the direction of motion of the beam is deflected by a deflector (not shown) to be parallel to the orbital plane 20a.

[0112] At this time, in the present embodiment, the beam-incident through-hole 115 and the incident position 130 are disposed closer to the center 20c of the magnetic poles 123a, 123b than in the comparative example (conventional configuration) shown in FIG. 1. Figure 12 Figure 13 The variable-energy accelerator of the comparative example (conventional configuration) shown in FIG. 1 is closer to the center 20c of the magnetic poles 123a, 123b than the present embodiment, and thus can reduce the component of the magnetic field 90a orthogonal to the incident beam path. Therefore, the electric field of the kick electrode 91 that applies a kick to balance the Lorentz force can be made smaller than in the comparative example. Figure 12 As a result, the amount of the incident beam that can be incident on the incident position 130 can be increased compared to the comparative example, and the amount of the charge that can be accelerated and irradiated can be increased in one operating cycle. Figure 12

[0113] The beam that has passed through the beam-passing region 20 is accelerated based on the high-frequency electric field each time it passes through the acceleration gap 223, its energy increases, and the radius of rotation of the orbit increases. Thereafter, the beam is accelerated to the desired energy while ensuring stability of the traveling direction based on the high-frequency electric field.

[0114] As described above, the frequency of the high-frequency electric field excited in the acceleration gap 223 is set to be synchronized at exactly an integral multiple of the rotation frequency of the beam. In the present embodiment, the particles are set to pass through the acceleration gap 223 at a predetermined phase at which the high-frequency electric field decreases with time, not at the timing at which the high-frequency electric field becomes the maximum. Therefore, the particles that have passed through the acceleration gap 223 to be accelerated at the predetermined phase of the high-frequency electric field are also accelerated at approximately the same phase in the next turn. On the other hand, the particles that have passed through the acceleration gap 223 to be accelerated at an earlier phase than the predetermined phase of the high-frequency electric field are accelerated by a larger amount than the particles that have passed through the acceleration gap 223 to be accelerated at the predetermined phase, and thus pass through the acceleration gap 223 at a later phase than the previous turn in the next turn. In addition, conversely, the particles that have passed through the acceleration gap 223 to be accelerated at a later phase than the predetermined phase are accelerated by a smaller amount than the particles that have passed through the acceleration gap 223 to be accelerated at the predetermined phase, and thus pass through the acceleration gap 223 at an earlier phase than the previous turn in the next turn. In this way, for the particles that pass through the acceleration gap 223 at a timing deviating from the predetermined phase, a restoring action to return to the predetermined phase acts, and by this action, the particles stably oscillate in a phase plane (traveling direction) constituted of the amount of motion variance (dispersion) Δp and the phase of the high-frequency. This oscillation is called synchrotron oscillation. That is, the particles in acceleration gradually increase in energy while performing synchrotron oscillation, and reach the predetermined energy. During stable synchrotron oscillation, each particle performs a rotational motion in a stable region called a high-frequency bucket in the phase plane. ​​

[0115] In order to extract a predetermined extraction beam from the accelerator 1 at the target energy, the overall control device 40 gradually reduces the amplitude of the high-frequency electric field applied to the high-frequency accelerating cavity 21, and controls the output of the low-level high-frequency generating device 42 and the amplifier 43 in such a way that the amplitude of the high-frequency electric field becomes 0 when the beam reaches the target energy. As a result, the beam rotates stably within the accelerator 1 at the target energy.

[0116] In this state, if a high-frequency voltage matching the frequency of the electron induction accelerator vibration of the beam is applied to the interference electrode 313, the beam is interfered with at a position dependent on its direction of travel, i.e., at the moment it passes through the interference electrode 313. Focusing on a specific particle, since the frequency of the interference electric field matches that of the rotating electron induction accelerator vibration, they resonate, increasing the amplitude of the particle's electron induction accelerator vibration. If the amplitude of this particle's electron induction accelerator vibration continues to increase, it passes through the area affected by the sudden magnetic field generated by the pad 311, produced by the additional magnetic field located outside the designed track. As a result, under the influence of the sudden magnetic field, the electron induction accelerator vibration diverges sharply, and the beam appears to shift outward from the designed track. Consequently, the beam reaches the extraction channel 312, passes through the extraction track 322, and is extracted to the outside through the extraction beam through-hole 111 of the accelerator 1.

[0117] As described above, from the time the beam reaches the target energy within accelerator 1 until it is removed from accelerator 1, the individual particles constituting the beam generate a quadrupole magnetic field and a multipole magnetic field with six or more poles through the additional magnetic field formed by the pad 311. In the phase space determined by the horizontal position and slope of the beam, they rotate in two states: a region capable of stable rotation and a region where the trajectory deviates unstablely and continuously increases. The boundary between this stable and unstable region is called the separatrix.

[0118] Furthermore, if the electric field applied to the interference electrode 313 is cut off, the increase in the amplitude of the electron induction accelerator vibration of the beam stops, and the beam rotates in the stable region, thus stopping the extraction of the beam.

[0119] use Figure 9 Charts and Figure 10 The flowchart describes the control actions of each device when the beam is accelerated by the principle described above and a beam of a certain energy is extracted outside the accelerator 1.

[0120] Figure 9The vertical axis of the graph, from top to bottom, represents the rotation angle of the rotation axis 213 of the rotary variable capacitance capacitor 212, the resonant frequency of the high-frequency accelerating cavity 21, the frequency of the high-frequency power input to the high-frequency accelerating cavity 21, the voltage amplitude of the high-frequency electric field in the accelerating gap 223, the beam current waveform output by the ion source 12, the amplitude of the interference high-frequency electric field input to the interference electrode 313, the horizontal emission (beam size) of the beam in the accelerator 1, and the beam current waveform output from the accelerator 1. Figure 9 The horizontal axis of the chart shown represents time.

[0121] Figure 10 The flow diagram represents the operation of the overall control device 40 and the voltage amplitude calculation device 45. The overall control device 40 and the voltage amplitude calculation device 45 are composed of a computer equipped with processors such as a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit) and memory. The CPU reads and executes the program stored in memory, thereby implementing the operation using software. Figure 10 The overall control device 40 and the voltage amplitude calculation device 45 can also be implemented in hardware, or in part or in whole. For example, custom ICs such as ASICs (Application Specific Integrated Circuits) and programmable ICs such as FPGAs (Field-Programmable Gate Arrays) can be used to construct the overall control device 40 and the voltage amplitude calculation device 45, or in whole or in part, to achieve the desired result. Figure 10 The circuit design can be based on the process of the operation.

[0122] If the irradiation begins from the point where the user has specified the beam's direction, then in Figure 10 In step 111, the voltage amplitude calculation device 45 reads the energy of the beam to be irradiated from the treatment plan database 60.

[0123] Next, in step 112, the overall control device 40 calculates the application time T of the high-frequency electric field required to accelerate the beam to the energy of the beam to be irradiated. Specifically, the overall control device 40 calculates the application time T of the high-frequency electric field required to accelerate to the energy of the read beam based on a table and mathematical formula that determines the relationship between the application time T of the high-frequency electric field required to accelerate to the energy of the beam, which is calculated in advance according to the energy of the beam. In addition, the overall control device 40 calculates the reduction start time T1d corresponding to the energy of the read beam based on a table and mathematical formula that determines the relationship between the voltage reduction time Td and the voltage reduction time Td calculated in advance according to the energy of the beam. This reduction start time T1d is the time when the high-frequency electric field for acceleration in the acceleration gap 223 becomes 0 when the voltage amplitude of the high-frequency power to the high-frequency acceleration cavity 21 is reduced or stopped at this time, and is the expected time when the beam reaches the target energy.

[0124] In step 113, the overall control device 40 instructs the motor control device 41 to activate the servo motor 214, such as... Figure 9 As shown, the rotating shaft 213 of the rotary variable capacitance capacitor 212 is rotated at a predetermined angular velocity. Based on the rotation angle of this rotating shaft 213, as... Figure 9 As shown, the resonant frequency f1 of the basic mode of the high-frequency accelerating cavity 21 changes periodically. During this time, the high-frequency power for acceleration has not yet been input into the high-frequency accelerating cavity 21.

[0125] In step 114, as Figure 9 As shown, the overall control device 40 outputs a beam from the ion source 12 within a predetermined time after the start of the operating cycle. Thus, the ion beam is incident from the incident position 130 of the accelerator 1 into the interior of the accelerator 1 for a predetermined time.

[0126] At this time, a pre-calculated electric field is applied from electrode 91 to the beam incident through-hole 115 to balance the Lorentz force on the ion beam, thereby improving the incident efficiency of the ion beam at the incident position 130.

[0127] In step 115, from immediately after the ions are injected from the ion source 12, the overall control device 40 inputs high-frequency power of a frequency f2 that is the voltage amplitude E1 calculated by the voltage amplitude calculation device 45 in step 111 and that is synchronized with the resonance frequency fl of the fundamental mode of the high-frequency acceleration cavity 21 that varies according to the rotation angle of the rotation axis 213, from the low-level high-frequency generation device 42 and the amplifier 43 to the high-frequency acceleration cavity 21. As a result, the beam that is in a range in which stable synchrotron oscillation is possible that is injected into the accelerator 1 passes through the acceleration gap 223, and thereby rotates inside the accelerator 1 while being accelerated by the high-frequency electric field E. In contrast, particles in which synchrotron oscillation is not stable are not accelerated, collide with the structure inside the accelerator 1, and disappear. As the resonance frequency decreases, the beam is accelerated, and is accelerated to near the predetermined extraction energy.

[0128] In step 116, if the time Tldetermined in step 112 is reached from the start of the input of the high-frequency power, the amplitude E of the high-frequency voltage is stopped. The acceleration high-frequency electric field generated by the high-frequency acceleration cavity 21 gradually decreases (decreases gradually) in voltage amplitude based on the Q value of the resonance of the high-frequency acceleration cavity 21, and the high-frequency bucket described above gradually disappears.

[0129] In step 117, the overall control device 40 instructs the interference high-frequency control device 47 to rise from this time Tld. As a result, the interference high-frequency control device 47 causes the high-frequency power supply 46 to operate, and outputs high-frequency power to the interference electrode 313. The voltage value of the high-frequency power output from the high-frequency power supply 46 to the interference electrode 313 is controlled by the interference high-frequency control device 47, and the specified value is determined by the treatment planning database 60 as a value that is uniquely determined according to the extraction beam energy and the output current of the extraction beam, and is instructed by the overall control device 40. The interference electrode 313 generates an interference high-frequency electric field, and the beam that rotates in the accelerator 1 is disturbed by this electric field, and as shown in FIG. 6, the horizontal emittance increases. Figure 9

[0130] In step 118, at the time point at which the application time T determined in step 112 has elapsed, the voltage amplitude of the acceleration high-frequency electric field becomes zero. At the time point at which the voltage amplitude of the acceleration high-frequency electric field becomes sufficiently small, the beam inside the accelerator 1 reaches the predetermined extraction energy.

[0131] Meanwhile, the horizontal emittance (beam size) of the beam increases due to the effect of the interference high-frequency electric field from the interference electrode 313, passes through the region affected by the kick magnetic field excited by the additional magnetic field generation pad 311, reaches the range affected by the magnetic field formed by the extraction slit electromagnet 312, passes through the extraction orbit 322, and is extracted to the outside from the extraction beam through-hole 111 of the accelerator 1.

[0132] ​In step 119, the overall control device 40 continues to apply the interference high-frequency electric power to the interference electrode 313 until the time for the extraction of the beam passes the time decided in advance by the treatment planning database 60. During this period, the extraction of the beam from the accelerator 1 is continued by the action of the interference high-frequency electric field of the interference electrode 313. The beam extraction time is set to the time when all the charges in rotation are extracted from the accelerator 1 in total, or the time when the extracted beam reaches a predetermined irradiation dose decided by the treatment plan. In the present embodiment, the extraction at the time of the high efficiency from the accelerator 1 can be performed, and thus the beam extraction time can be set to be shorter than in the past.

[0133] During this period, the servo motor 214 accompanying the high-frequency accelerating cavity 21 continues to rotate, and the resonance frequency continues to vary, but since the accelerating high-frequency is not input to the high-frequency accelerating cavity 21, almost no influence on the beam is generated. Thus, the beam continues to rotate at a fixed energy, and is extracted in turn by the applied interference high-frequency.

[0134] If the beam extraction time passes, the overall control device 40 proceeds to step 120, and stops the application of the interference high-frequency electric power to the interference electrode 313. Although depending on the strength of the disturbance high-frequency, the opening / closing of the beam can be controlled by opening / closing the disturbance high-frequency. Further, as shown in Figure 9 indicated, the beam can also be extracted during a period longer than the operation period. In addition, the operation period referred to here is the period from the time when the resonance frequency becomes the maximum to the time when the next becomes the maximum.

[0135] When the irradiation ends, the voltage amplitude calculation device 45 reads in the energy of the beam that should be extracted next from the treatment planning database, and returns to step 111. Steps 112 and subsequent are performed as with the above-described flow. In Figure 9 In the example shown in FIG. 10, in the latter operation period, the beam is irradiated with an energy larger than in the previous operation period, and thus the application time T2 of the high-frequency electric field is set to be longer than the application time Tl of the accelerating high-frequency electric field in the previous operation period, and the beam is accelerated to a larger energy.

[0136] The accelerator of the present embodiment is small in size and capable of changing the energy of the extracted beam by focusing on the position of the beam-incident through-hole 115 and the moving direction of the rotation track, and can improve the efficiency of the beam incidence from the external ion source into the accelerator. As a result, the dose rate of the extracted ion beam can be improved.

[0137] <Second Embodiment>

[0138] The particle beam therapy system of the second embodiment of the present application will be described. The same reference numerals are assigned to the same structures as in the first embodiment, and the description will be omitted. Figure 11 The particle beam therapy system of the second embodiment of the present application will be described. The same reference numerals are assigned to the same structures as in the first embodiment, and the description will be omitted.

[0139] The second embodiment is a particle beam therapy system using the accelerator 1 of the first embodiment. Figure 11 An overall configuration diagram of the system is shown.

[0140] The particle beam therapy system 1000 is a device that irradiates a patient 5 with a proton beam or a carbon beam (hereinafter collectively referred to as a beam) of an appropriate energy value to a lesion (target) of the patient 5 according to the depth of the lesion from the body surface. As shown in the figure, the particle beam therapy system 1000 is provided with an accelerator 1 that accelerates ions, a beam transport system 2 that transports a beam accelerated by the accelerator 1 to an irradiation device described later, the irradiation device 3 that irradiates a target in the patient 5 fixed to a treatment table 4 with a beam transported by the beam transport system 2, a general control device 40 and an irradiation control device 50 that control the accelerator 1, the beam transport system 2, and the irradiation device 3, a treatment planning device 70 that makes an irradiation plan of a beam for a target, and a treatment planning database 60 that stores a treatment plan made by the treatment planning device 70. In addition, the accelerator 1 is connected to the extraction passage 312 described in the first embodiment, and a beam can be extracted by the structure described in the first embodiment. Figure 11

[0141] In the particle beam therapy system 1000, the energy and the dose of the irradiated particle beam are determined by reading in the data of the treatment plan stored in the treatment planning database 60. The energy and the dose of the particle beam determined by the treatment plan are sequentially input from the general control device 40 to the irradiation control device 50, and at the time point when the appropriate dose is irradiated, the particle beam is irradiated again at the next energy.

[0142] In addition, the beam transport system 2 of the particle beam therapy system 1000 is not limited to the fixed system as shown in the figure, and can be configured as a transport system that can rotate around the patient 5 in accordance with an irradiation device called a rotating gantry. In addition, the irradiation device 3 is not limited to one, and a plurality of irradiation devices 3 can be provided. Furthermore, it can be configured as a mode in which the beam transport system 2 is not provided and a beam is directly transported from the accelerator 1 to the irradiation device 3. Figure 11

[0143] <Other>

[0144] Furthermore, the present application is not limited to the above-described embodiments, and various modifications are included. The above-described embodiments are embodiments that are described in detail in order to easily understand the present application, and are not limited to necessarily having all the structures described.

[0145] Explanation of symbols

[0146] 1…Accelerator

[0147] 2…Beam transport system ​​

[0148] 3… irradiation device

[0149] 11… electromagnet

[0150] 12… ion source

[0151] 13… coil

[0152] 20… beam passing region

[0153] 20a… orbital plane

[0154] 21… high frequency acceleration cavity

[0155] 33… trim coil

[0156] 40… overall control device

[0157] 41… motor control device

[0158] 42… low level high frequency generating device

[0159] 43… amplifier

[0160] 46… high frequency power supply

[0161] 47… interference high frequency control device

[0162] 50… irradiation control device

[0163] 60… treatment planning database

[0164] 91… electrode

[0165] 111… through hole for extracted beam

[0166] 112… through hole for coil connection

[0167] 114… through hole for high frequency power input

[0168] 115… through hole for beam incidence

[0169] 121… side yoke

[0170] 122… top plate

[0171] 123… magnetic pole

[0172] 130… incidence position

[0173] 211… input coupler

[0174] 212… rotary variable capacitance capacitor

[0175] 213… rotation shaft

[0176] 214… servo motor

[0177] 221... D-shaped electrode

[0178] 222... Ground electrode

[0179] 223... Acceleration gap

[0180] 311... Pad for additional magnetic field generation

[0181] 312... Extraction channel

[0182] 313... Interference electrode

[0183] 322... Extraction rail

[0184] 1000... Particle beam therapy system

Claims

1. An accelerator characterized by, having: an electromagnet including a pair of magnetic poles facing each other across an orbit surface on which an ion beam rotates, and forming a main magnetic field that generates a plurality of rotating orbits at the orbit surface; an ion incidence through-hole formed in the magnetic pole for introducing an ion beam from the outside to a predetermined incidence position of the orbit surface; a high-frequency acceleration cavity inserted into a gap formed between the pair of magnetic poles, generating high frequency for accelerating the ion beam rotating around the orbit surface; and an additional magnetic field generating portion and an extraction passage, the additional magnetic field generating portion being arranged at an outer periphery of the gap, applying a magnetic field to the ion beam moving on one or more of the rotating orbits at an outermost periphery and an inner side of the outermost periphery to deviate the moving direction from the rotating orbits, the extraction passage guiding the ion beam deviated from the rotating orbits to the outside of the gap, the intensity distribution in the orbit surface of the main magnetic field being designed such that, as the ion beam is accelerated, the radius of the rotating orbit gradually increases, and after moving in a predetermined radial direction of the gap toward the periphery portion, the moving direction is reversed to further move toward the center of the gap.

2. The accelerator according to claim 1, wherein the intensity distribution of the main magnetic field of the electromagnet is designed such that the center of the rotating orbit moves in the predetermined radial direction of the gap toward the periphery portion of the gap until the radius thereof reaches a predetermined first radius, and after reaching the first radius, moves in the radial direction toward the center of the gap.

3. The accelerator according to claim 1, wherein the pair of magnetic poles are each cylindrical, having a magnetic pole surface arranged in a symmetrical manner across the orbit surface, the ion incidence through-hole is provided at a position where a central axis is perpendicular to the orbit surface and orthogonal to the predetermined radial direction.

4. The accelerator according to claim 1, wherein the distance between the central axis of the ion incidence through-hole and the center of the gap is set within 50% of the length of the radius of the gap.

5. The accelerator according to claim 3, wherein a gasket is arranged at a position between the ion incidence through-hole and the center of the magnetic pole and adjacent to the ion incidence through-hole in the magnetic pole surface.

6. The accelerator according to claim 5, wherein the ion incidence through-hole and the gasket are each provided at a position symmetrical across the orbit surface on the opposite magnetic pole, the distance between the pair of gaskets is narrower than the distance between the pair of magnetic pole surfaces at a position adjacent to the ion incidence through-hole in the predetermined radial direction between the ion incidence through-hole and the outer periphery of the magnetic pole surface, or the distance of the gasket arranged at the position.

7. The accelerator according to claim 1, wherein an ion source that emits an ion beam to the ion incidence through-hole is provided outside the electromagnet.

8. The accelerator according to claim 1, wherein The extraction passage is arranged at the outer periphery of the predetermined radial direction of the gap.

9. The accelerator according to claim 5, wherein The magnetic field gradient at the position where the gasket is arranged is the largest among the magnetic field gradients at the positions between the through-hole for ion incidence and the center of the pole in the radial direction.

10. The accelerator according to claim 9, wherein The magnetic field gradient at the position between the through-hole for ion incidence and the outer periphery of the gap in the radial direction is the largest at the peripheral edge of the gap.

11. The accelerator according to claim 3, wherein A plurality of annular fine adjustment coils are provided on the pole face, and the fine adjustment coils are arranged at the positions of the pole face corresponding to the plurality of the rotation tracks and the radii of the track plane.

12. The accelerator according to claim 1, wherein The high-frequency acceleration cavity includes a D-shaped electrode, and edges of the D-shaped electrode are arranged so as to cross the gap in parallel with the track plane, and the edges have a W-shaped form centered on the vicinity of the incidence position.

13. A particle beam therapy system that irradiates a particle beam to a patient, wherein As a generating device of the particle beam, the accelerator according to any one of claims 1 to 12 is used.

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