WO2018042538A1

WO2018042538A1 - Particle beam radiation apparatus

Info

Publication number: WO2018042538A1
Application number: PCT/JP2016/075459
Authority: WO
Inventors: 智媛李; 山本　和男; 松田　哲也; 博光井上
Original assignee: 三菱電機株式会社
Priority date: 2016-08-31
Filing date: 2016-08-31
Publication date: 2018-03-08
Also published as: TW201811395A

Abstract

The purpose of the present invention is to provide a small particle beam radiation apparatus which has a rotational gantry that is equipped with an accelerator which is lightweight due to employing a superconducting air core coil. This particle beam radiation apparatus (59) includes a particle beam circular accelerator (51) that is supported by a rotational gantry (60), a beam transport system (54), and a radiation field forming device (56). The particle beam circular accelerator (51) includes: a pair of superconducting coils (3a, 3b) which are symmetrically arranged with respect to an acceleration trajectory surface (12); and a pair of pole tips (7a,7b) which are arranged inside the superconducting coils (3a, 3b), are symmetrically arranged with respect to the acceleration trajectory surface (12), and produce, from a magnetic field generated by the superconducting coils (3a, 3b), a magnetic field distribution that causes a charged particle beam (16) to move orbitally in an accelerating cavity (11). Each pole tip (7a,7b) has a thin portion (26) which is where the thickness between the inner surface (18) and outer surface (22) is smallest, the thin portion (26) being arranged such that at least half of the thin portion (26) is present on the outer periphery side of an intermediate line (29) which is located midway between a coil axis (17) and the outer peripheral edge of the pole tip (7a,7b).

Description

Particle beam irradiation equipment

The present invention relates to a particle beam irradiation apparatus for irradiating an affected area such as cancer with a charged particle beam such as a proton beam or a carbon ion beam.

Patent Document 1 discloses a particle beam irradiation apparatus in which a cyclotron, which is a particle beam circular acceleration means for generating a charged particle beam such as a proton beam and accelerating to high energy, is arranged outside a rotating gantry (see FIG. 23 of Patent Document 1). And a particle beam irradiation apparatus (see FIG. 1 of Patent Document 1) in which a cyclotron is mounted on a rotating gantry. In this cyclotron, the structure of an electromagnet that applies a magnetic field to the particle beam acceleration orbital surface is constituted by a superconducting coil. Further, Patent Document 1 describes that the particle beam circular acceleration means mounted on the rotating gantry may be a synchrocyclotron. While the cyclotron outputs a charged particle beam as a continuous beam, the synchrocyclotron is configured to output a charged particle beam as a pulse beam.

A circular ion accelerator (particle beam circular acceleration means) of a synchrocyclotron equipped with a superconducting coil is described in Patent Document 2, for example. The synchrocyclotron of Patent Document 2 includes a superconducting coil pair, a cryostat that holds the superconducting coil pair under vacuum, and a magnetic yoke structure that surrounds the cryostat. The magnetic yoke structure includes an upper yoke 31, a lower yoke 32, magnetic

pole part pairs

33 and 34, and a return yoke 35. The magnetic yoke structure magnetic pole part pair (upper magnetic pole part 33, lower magnetic pole part 34) is disposed in an internal space including the coil axis (center axis 50) of the superconducting coil pair (upper coil 20, lower coil 25). . The upper magnetic pole portion 33 connected to the upper yoke 31 and the lower magnetic pole portion 34 connected to the lower yoke 32 are respectively extended to the vicinity of the particle beam acceleration orbit plane of the synchrocyclotron. Also, in a cyclotron equipped with a superconducting coil, the upper magnetic pole part connected to the upper yoke and the lower magnetic pole part connected to the lower yoke are usually connected to the synchrocyclotron particle beam, as in the synchrocyclotron disclosed in Patent Document 2. It is extended to the vicinity of the acceleration orbital surface.

Japanese Patent No. 3472657 (FIGS. 1 and 23) Published US 2013 / 0270451A1 (Steps 0027 to 0031, FIGS. 1 and 2)

Patent Document 1 describes a particle beam therapy system in which a cyclotron is mounted on a rotating gantry. However, since the magnetic yoke structure surrounding the superconducting coil pair and the cryostat is heavy, it is necessary to use a large and durable rotating gantry. In addition, the building of the facility where the rotating gantry is installed must have a large and strong building that can hold heavy objects.

The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a compact particle beam irradiation apparatus by mounting a lightweight accelerator by adopting a superconducting air-core coil on a rotating gantry. To.

The particle beam irradiation apparatus of the present invention generates a charged particle beam and accelerates it while rotating it by a magnetic field, a beam transport system for transporting a charged particle beam accelerated by the particle beam circular accelerator, and beam transport An irradiation field forming device that irradiates a target with a charged particle beam transported by the system, and a rotating gantry that supports the particle beam circular accelerator, beam transport system, and irradiation field forming device and that rotates the irradiation direction of the charged particle beam A particle beam irradiation apparatus. The particle beam circular accelerator is an acceleration cavity for accelerating a charged particle beam, a pair of superconducting coils arranged symmetrically with respect to the acceleration orbital surface of the charged particle beam, and an inner surface of the superconducting coil. And a pair of pole tips that form a magnetic field distribution in which a charged particle beam circulates in an acceleration cavity from a magnetic field generated by a superconducting coil. The pole tip of the particle beam irradiation device has a different thickness in the radial direction, which is the thickness of the inward surface facing the acceleration orbital surface and the outward surface farther from the inward surface, and is perpendicular to the radial direction of the superconducting coil. The central part containing the coil axis passing through the center of the superconducting coil and the radially outer peripheral part are thinner than the central part and the outer peripheral part and have the smallest thin part. It is characterized in that more than half of the arrangement area is arranged on the outer peripheral side with respect to the intermediate line between the coil shaft and the outer peripheral end of the pole tip.

In the particle beam irradiation apparatus of the present invention, the particle beam circular accelerator includes a pair of superconducting coils and a pair of pole tips disposed inside the superconducting coils, and more than an intermediate line between the coil shaft and the outer peripheral end of the pole tip. Since the thin part of the pole tip is arranged so as to be more than half on the outer peripheral side, a lightweight accelerator can be mounted on the rotating gantry, and the particle beam irradiation apparatus can be miniaturized.

It is a schematic block diagram of the particle beam irradiation apparatus by Embodiment 1 of this invention. It is sectional drawing which shows schematic structure of the particle beam circular accelerator by Embodiment 1 of this invention. FIG. 3 is a bird's-eye view of the fixed structure and the pole tip in FIG. 2. It is a figure explaining the beam emission of the particle beam circular accelerator of FIG. It is sectional drawing which shows the 1st example of the pole tip of FIG. FIG. 6 is a bird's-eye view of the pole tip in FIG. 5. It is a figure which shows the outward surface of the pole tip of FIG. It is a figure which shows the magnetic field distribution of the particle beam circular accelerator of FIG. It is a figure which shows the magnetic field distribution of the superconducting coil of FIG. It is a figure which shows the magnetic field distribution of the pole tip of FIG. 2, and a pole tip. It is sectional drawing which shows the 2nd example of the pole tip of FIG. It is a bird's-eye view of the pole tip of FIG. It is a figure which shows the outward surface of the pole tip of FIG. It is sectional drawing which shows the 3rd example of the pole tip of FIG. It is a bird's-eye view of the pole tip of FIG. It is a figure which shows the outward surface of the pole tip of FIG. It is sectional drawing which shows the 4th example of the pole tip of FIG. It is a bird's-eye view of the pole tip of FIG. It is a figure which shows the outward surface of the pole tip of FIG. It is sectional drawing which shows schematic structure of the particle beam circular accelerator by Embodiment 2 of this invention. FIG. 21 is a bird's-eye view of the fixed structure and the pole tip of FIG. 20. It is sectional drawing which shows the 1st example of the pole tip of FIG. 20, and a superconducting coil. It is sectional drawing which shows the 1st example of the pole tip of FIG. It is a figure which shows the inward surface of the pole tip of FIG. It is a figure which shows the outward surface of the pole tip of FIG. It is an enlarged view of the pole tip of FIG. It is sectional drawing which shows the 2nd example of the pole tip of FIG. It is a bird's-eye view of the pole tip of FIG. It is a figure which shows the inward surface of the pole tip of FIG. It is sectional drawing which shows the 3rd example of the pole tip of FIG. FIG. 31 is a bird's-eye view of the pole tip of FIG. 30. It is a figure which shows the outward surface of the pole tip of FIG.

Embodiment 1 FIG.
FIG. 1 is a schematic configuration diagram of a particle beam irradiation apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a cross-sectional view illustrating a schematic configuration of a particle beam circular accelerator according to Embodiment 1 of the present invention. FIG. 3 is a bird's-eye view of the fixed structure and the pole tip of FIG. FIG. 4 is a view for explaining beam emission of the particle beam circular accelerator of FIG. FIG. 5 is a cross-sectional view showing a first example of the pole tip of FIG. 6 is a bird's-eye view of the pole tip of FIG. 5, and FIG. 7 is a view showing the outward surface of the pole tip of FIG. 8 is a diagram showing the magnetic field distribution of the particle beam circular accelerator of FIG. 2, and FIG. 9 is a diagram showing the magnetic field distribution of the superconducting coil of FIG. FIG. 10 is a diagram showing the pole tip of FIG. 2 and the magnetic field distribution of the pole tip. FIG. 11 is a cross-sectional view showing a second example of the pole tip of FIG. 12 is a bird's-eye view of the pole tip shown in FIG. 11, and FIG. 13 is a view showing an outward surface of the pole tip shown in FIG. FIG. 14 is a cross-sectional view showing a third example of the pole tip of FIG. 15 is a bird's-eye view of the pole tip shown in FIG. 14, and FIG. 16 is a view showing the outward surface of the pole tip shown in FIG. 17 is a cross-sectional view showing a fourth example of the pole tip of FIG. 18 is a bird's-eye view of the pole tip of FIG. 17, and FIG. 19 is a view showing the outward surface of the pole tip of FIG.

The particle beam irradiation apparatus 59 of the first embodiment generates a particle beam such as a proton beam, that is, a charged particle beam 16 (see FIG. 4), and emits a charged particle beam 16 that is accelerated while being rotated by a magnetic field. An accelerator 51, a beam transport system 54 for transporting the charged particle beam 16 accelerated to the required energy by the particle beam circular accelerator 51 to the irradiation field forming device 56, and the charged particle beam 16 transported by the beam transport system 54 The irradiation field forming device 56 for irradiating the patient 58 as an irradiation target, the particle beam circular accelerator 51, the beam transport system 54, and the irradiation field forming device 56 are supported (mounted), and charged particles from any direction with respect to the patient 58 A rotating gantry 60 for irradiating the beam 16 is provided. The patient 58 is mounted and fixed on a treatment table 57 installed in the treatment room 65. The beam transport system 54 includes a beam transport tube 55 through which the charged particle beam 16 passes, a plurality of

quadrupole electromagnets

52a, 52b, 52c, and 52d that focus the charged particle beam 16, and a plurality of deflections that bend the trajectory of the charged particle beam 16.

Electromagnets

53a and 53b are provided. The rotating gantry 60 includes

rotating frames

61a and 61b,

rollers

62a and 62b that rotatably support the

rotating frames

61a and 61b, a rotation driving device 63 that drives the

rotating frames

61a and 61b, and

rotating frames

61a and 61b. A counterweight 64 that balances the weight in a state in which the device is attached is provided. The rotating gantry 60 is installed on a building floor 68 arranged at a position lower than the floor of the treatment room 65. Between the treatment room 65 and the particle beam circular accelerator 51, a shielding structure 66 for shielding radiation, which is formed in a cylindrical shape with the particle beam circular accelerator 51 side closed, is installed. On the treatment room ceiling 67, floor, and wall of the treatment room 65, there is provided a device passage groove 69 that is a notch or the like that allows the irradiation field forming device 56 to rotate around the rotation axis of the rotating gantry 60.

In the particle beam irradiation apparatus 59 shown in FIG. 1, in the particle beam circular accelerator 51, the acceleration orbit plane of the charged particle beam 16 is perpendicular to the central axis of the

rotating frames

61a and 61b, that is, the rotating axis of the rotating gantry 60. The charged particle beam 16 is configured to be emitted from the outer periphery of the particle beam circular accelerator 51 in a direction perpendicular to the central axis (upward in FIG. 1). That is, the particle beam circular accelerator 51 is connected to the beam transport system 54 such that the acceleration orbit plane of the charged particle beam 16 is mounted at right angles to the rotation axis of the rotating gantry 60. The charged particle beam 16 emitted from the particle beam circular accelerator 51 is focused by the

quadrupole electromagnets

52a, 52b, 52c, and 52d, the transport direction is changed by the

deflection electromagnets

53a and 53b, and transported through the beam transport tube 55 to be irradiated. The forming device 56 is entered. The charged particle beam 16 is irradiated to the target (affected part) of the cancer cell of the patient 58 that is the irradiation target placed on the treatment table 57 by the irradiation field forming device 56. In the particle beam irradiation device 59, a particle beam circular accelerator 51,

quadrupole electromagnets

52a, 52b, 52c, 52d,

deflection electromagnets

53a, 53b, and an irradiation field forming device 56 are attached to

rotating frames

61a, 61b. The rotary frames 61a and 61b are configured to rotate, and the irradiation field forming device 56 is disposed so that the extension line in the irradiation direction of the charged particle beam 16 and the center line of the rotation axis intersect. Therefore, in the particle beam irradiation apparatus 59, the irradiation field forming apparatus 56 is rotatably arranged by the rotating gantry 60, and the irradiation field forming apparatus 56 intersects the extension line in the irradiation direction of the charged particle beam 16 and the rotation axis. Therefore, it is possible to irradiate the cancer cells of the patient 58 with a particle beam from an arbitrary direction.

The particle beam circular accelerator 51 includes a cryostat 1 that maintains a vacuum inside, a fixed structure 2,

superconducting coils

3a and 3b that generate a deflection magnetic field,

active shield coils

4a and 4b that reduce a leakage magnetic field, and heat transfer.

Plates

5a, 5b, 6a, 6b,

pole tips

7a, 7b, ion source 8 for generating charged particles, Dee electrode 9, dummy Dee electrode 10, and acceleration cavity for accelerating charged particles (charged particle beam 16) 11 is provided. The particle beam circular accelerator 51 is, for example, a synchrocyclotron or a cyclotron. The coil shaft 17 is a central axis perpendicular to the radial direction of the

superconducting coils

3a and 3b and passing through the centers of the

superconducting coils

3a and 3b. The

pole tips

7a and 7b are arranged inside the

superconducting coils

3a and 3b, and form a magnetic field distribution in which the charged particles circulate in the acceleration cavity 11. A center line 28 perpendicular to the radial direction of the

pole tips

7a and 7b and passing through the centers of the

pole tips

7a and 7b is disposed on the coil shaft 17. As shown in FIG. 4, the charged particles generated in the ion source 8 are distributed between the magnetic field distribution formed by the

superconducting coils

3 a and 3 b and the

pole tips

7 a and 7 b, the dee electrode 9, and the dummy dee electrode 10. The generated high-frequency electric field accelerates the midplane 12 that is the acceleration orbital surface, and circulates while increasing the orbital radius. The

pole tips

7a and 7b form a magnetic field distribution for circulating charged particles (charged particle beam 16) in the acceleration cavity 11 from the magnetic field generated by the

superconducting coils

3a and 3b.

The particle beam circular accelerator 51 is an accelerator that does not include a yoke as in Patent Document 2, and includes an air core coil (air core type coil) and a pole tip disposed inside the air core coil. Superconducting coils 3a and 3b and

active shield coils

4a and 4b are air-core coils. Superconducting coil 3a, heat transfer plate 5a, pole tip 7a, active shield coil 4a, heat transfer plate 6a, superconducting coil 3b, heat transfer plate 5b, pole tip 7b, active shield coil 4b, heat transfer plate 6b are midplanes. 12 are arranged symmetrically. The pole tip 7a and the pole tip 7b have the same planar shape and cross-sectional shape. The

heat transfer plates

5 a and 5 b are connected to the

superconducting coils

3 a and 3 b and the fixed structure 2, respectively, and dissipate heat generated in the

superconducting coils

3 a and 3 b to the fixed structure 2. The

heat transfer plates

6 a and 6 b are connected to the

active shield coils

4 a and 4 b and the fixed structure 2, respectively, and radiate heat generated in the

active shield coils

4 a and 4 b to the fixed structure 2.

The fixed structure 2 includes a top plate 41, a bottom plate 42, an outer peripheral cylinder 43, and an inner peripheral cylinder 44, and has a cylindrical shape in which a central portion surrounded by the inner peripheral cylinder 44 is hollowed out. Superconducting coils 3a and 3b,

heat transfer plates

5a and 5b,

pole tips

7a and 7b,

active shield coils

4a and 4b,

heat transfer plates

6a and 6b, ion source 8, dee electrode 9 and dummy dee electrode 10 are fixed structures. Fixed to the body 2. Specifically,

pole tips

7a and 7b, an ion source 8, a dee electrode 9, and a dummy dee electrode 10 are disposed in the center, and an acceleration cavity 11 is formed in the center. The superconducting coils 3a and 3b, the

heat transfer plates

5a and 5b, the

pole tips

7a and 7b, the

active shield coils

4a and 4b, and the

heat transfer plates

6a and 6b are the top plate 41, the bottom plate 42, the outer cylinder 43, and the inner cylinder. It is fixed in a closed space surrounded by 44.

As shown in FIG. 4, the particle beam circular accelerator 51 generates a high-frequency electric field between the dee electrode 9 and the dummy dee electrode 10 to accelerate charged particles generated in the ion source 8. The charged particles pass through the Dee electrode 9 and the dummy Dee electrode 10 alternately and are accelerated to increase the orbit radius while keeping the rotation period constant. The charged particles are accelerated to obtain a predetermined kinetic energy, and are emitted to the beam transport system 54 by the beam extraction device 15. A beam transport tube 55 extending from the outer periphery of the cryostat 1 is connected to the fixed structure 2. The fixed structure 2 has an opening communicating with the beam transport tube 55. In FIG. 4, the Y axis, which is the direction in which the high-frequency electric field is generated, and the X axis perpendicular to the Y axis are shown.

Next, the

pole tips

7a and 7b will be described. The pole chip is generally denoted by 7, and 7a and 7b are used in the case of distinction. As shown in FIGS. 5 and 6, the pole tip 7 is arranged on the side of the midplane 12 (see FIG. 2), that is, an inward surface 18 facing the midplane 12, and a midplane rather than the inward surface 18. 12 has an outward surface 22 arranged far from 12, and has a cross-sectional shape in which the thickness of the inward surface 18 and the outward surface 22 changes from the center line 28 toward the outer peripheral side. Center line 28 is perpendicular to midplane 12. The pole tip 7 which is the first example of the pole tip shown in FIGS. 5 to 7 is an example in which the inward surface 18 and the outward surface 22 are uneven. As shown in FIG. 7, the pole tip 7 has a circular outer periphery of the outward face 22 and the inward face 18.

The pole tip 7 has, on the outward face 22 side, an outward convex part 24 formed so as to enclose the center line 28, an outward flat part 23 formed on the outer peripheral side of the outward convex part 24, An outward-side outer peripheral convex portion 25 formed on the outer peripheral side of the side flat portion 23 is provided. Further, the pole tip 7 has, on the inward surface 18 side, an inward convex portion 20 formed so as to contain the center line 28, and an inward flat portion 19 formed on the outer peripheral side of the inward convex portion 20. The inward-side outer peripheral convex portion 21 is provided on the outer peripheral side of the inward-side flat portion 19. The outward flat portion 23 and the inward flat portion 19 are parallel to the midplane 12. The outward flat portion 23 is formed closest to the inner peripheral surface 13, and the inward flat portion 19 is formed closest to the outward surface 22. The outward-side convex portion 24 and the outward-side outer peripheral convex portion 25 protrude from the outward-side flat portion 23 in the direction of the coil shaft 17 (center line 28) and away from the inward surface 18. The inward-side convex portion 20 and the inward-side outer peripheral convex portion 21 protrude from the inward-side flat portion 19 in the direction of the coil shaft 17 (center line 28) and away from the outward surface 22. It should be noted that the outward convex portion 24, the outward flat portion 23, the outward outward convex portion 25 on the outward surface 22 side, the inward convex portion 20, the inward flat portion 19, and the inward peripheral convex portion on the inward surface 18 side. The boundary which divides the part 21 is the flat part thickness intermediate line 45 of the intermediate | middle thickness of the outward flat part 23 and the inward flat part 19, for example.

Using the broken lines A1, A2, A3, A4, B1, B2, B3, and B4 parallel to the center line 28, the outward convex portion 24, the outward flat portion 23, the outward peripheral convex portion 25, and the inward convex portion 20 are used. The range of the inward-side flat portion 19 and the inward-side outer peripheral convex portion 21 will be described. In FIG. 5, the outward-side convex portion 24 is between the broken line A2 and the broken line A3, and the outward-side flat portion 23 is between the broken line A1 and the broken line A2, and between the broken line A3 and the broken line A4. The convex portion 25 is between the broken line A1 and the left end and between the broken line A4 and the right end. In FIG. 5, the inward convex portion 20 is between the broken line B2 and the broken line B3, and the inward side flat portion 19 is between the broken line B1 and the broken line B2 and between the broken line B3 and the broken line B4. The side outer peripheral convex portion 21 is between the broken line B1 and the left end and between the broken line B4 and the right end. The intermediate line 29 is an intermediate line between the center line 28 and the outer peripheral end of the pole tip 7. The outer peripheral ends of the pole tip 7 are a left end and a right end of the pole tip 7 in FIG. The intermediate line 29 is a line parallel to the center line 28.

Since the pole tip 7 has irregularities on the inward surface 18 and the outward surface 22, the thickness perpendicular to the midplane 12 changes from the center line 28 toward the outer peripheral side. The thickness in the direction of the left end from the center line 28 is thickest at the central portion through which the center line 28 passes, decreases toward the broken line A2, becomes thinnest between the broken line A2 and the broken line B1, and increases toward the left end. It has become. Between the broken line A2 and the broken line B1, it is the thin part 26 with the thinnest thickness in the vertical direction. The thickness in the right end direction from the center line 28 is thickest at the central portion through which the center line 28 passes, decreases toward the broken line A3, becomes thinnest between the broken line A3 and the broken line B4, and increases toward the right end. It has become. Between the broken line A3 and the broken line B4 is the thin portion 26 having the smallest thickness in the vertical direction. The thickest central part is the thickest part (top) of the outward convex part 24 and the thickest part of the inward convex part 20. In addition, the thin part 26 on the left side and the thin part 26 on the right side in FIG. 5 are formed concentrically with the center line 28 as the center, like the inward flat part 19 and the outward flat part 23.

Next, the magnetic field distribution formed by the

superconducting coils

3a and 3b and the pole tip 7 will be described with reference to FIGS. FIG. 8 shows a magnetic field distribution 31 formed in the superconducting coil 3a and the pole tip 7a in the particle beam circular accelerator 51. FIG. 9 shows the magnetic field distribution 32 of the superconducting coil 3 a in the particle beam circular accelerator 51. Moreover, the outer peripheral side cross section of

superconducting coil

3a, 3b was shown with the broken line. FIG. 10 shows the pole tip 7a in the particle beam circular accelerator 51 and the magnetic field distribution 33 of the pole tip 7a. In the magnetic field distribution diagram, the horizontal axis is the radial position R from the center line 28, and the vertical axis is the magnetic field in the direction of the center line 28, that is, the magnetic field Bz in the Z direction. The direction of the magnetic field Bz from the inward surface 18 toward the outward surface 22 is a positive direction. In the radial position R, the direction from the center line 28 toward the outer peripheral edge is the positive direction. In the pole tip shape diagram shown in FIG. 10, the horizontal axis is the radial position R from the center line 28, and the vertical axis is the position in the center line 28 direction, that is, the position Z in the Z direction. The magnetic field distribution formed in the superconducting coil 3b and the pole tip 7b is a distribution obtained by inverting the magnetic field distribution 31 around the horizontal axis. The magnetic field distribution formed in the superconducting coil 3b is a distribution obtained by inverting the magnetic field distribution 32 around the horizontal axis. The magnetic field distribution formed on the pole tip 7b is a distribution obtained by inverting the magnetic field distribution 33 around the horizontal axis.

The magnetic field distribution 31 gradually decreases from the center line 28 where the radial position R is zero to the position ra1 in the radial direction, and decreases rapidly from the position ra1 to zero at the position ra2. Become. The magnetic field from the center line 28 to the position ra1 has a magnetic field strength for circulating the charged particles in the acceleration cavity 11, and the magnetic field from the position ra1 to the position ra2 has a magnetic field strength for emitting the charged particle beam 16 to the outside. That is, it has a magnetic field strength that does not cause the charged particles to circulate.

The magnetic field distribution 32 gradually increases from the center line 28 toward the position rc1 in the radial direction, and gradually decreases away from the position rc1. The magnetic field distribution 33 gradually decreases from the center line 28 toward the position rp2 toward the position rp2 in the radial direction based on the change in the radial thickness of the pole tip 7a, becomes minimal at the position rp2, and then increases to the position rp3. And then decreases to zero at position rp4. By superimposing the magnetic field distribution 32 and the magnetic field distribution 33, a desired magnetic field distribution 31 necessary for the particle beam circular accelerator 51 can be obtained.

The magnetic field distribution 33 will be described in detail with reference to FIG. The position rp1 is a boundary point where the thickness of the inward convex portion 20 decreases. A broken line C1 is a line passing through the boundary between the outward-side convex part 24 and the outward-side flat part 23, and a broken line C2 is a line passing through the boundary between the inward-side flat part 19 and the inward-side outer peripheral convex part 21. The broken line C3 is a line passing through the boundary where the thickness of the outward-side outer peripheral convex portion 25 is maximum, and the broken line C4 is a line passing through the outer peripheral end of the pole tip 7a. The area between the broken line C1 and the broken line C2 is the thin part 26 of the pole tip 7a, and the area between the broken line C3 and the broken line C4 is the outer peripheral thick part 27 that is the maximum thickness at the outer peripheral part of the pole tip 7a. is there. The thickness of the pole tip 7a decreases from the position rp1 toward the outer peripheral side to the broken line C1. The thickness of the pole tip 7a is minimized from the broken line C1 to the broken line C2, increases from the broken line C2 to the broken line C3, and maintains the maximum thickness at the outer periphery from the broken line C3 to the broken line C4. In addition, the thickness of the outer peripheral thick part 27 is equal to or thicker than the thickness in the central part. The thickness of the outer peripheral thick portion 27 is determined according to the decreasing gradient of the magnetic field strength from the position rp3 to the position rp4 of the magnetic field distribution 33. The greater the thickness of the outer peripheral thick portion 27, the steeper the decreasing gradient of the magnetic field strength from the position rp3 to the position rp4 of the magnetic field distribution 33.

FIG. 10 shows a quadrant 30 that is an intermediate line between the intermediate line 29 and the outer peripheral end of the pole tip 7a. Since the intermediate line 29 is an intermediate line between the center line 28 and the outer peripheral end of the pole tip 7a, the quadrant 30 is a line passing through a position of a quarter of the radius from the outer peripheral end of the pole tip 7a. In FIG. 10, the position rp2 at which the magnetic field intensity of the magnetic field distribution 33 becomes the minimum value is in the region of the thin portion 26 that is on the outer peripheral side of the intermediate line 29 of the pole tip 7a and on the outer peripheral side of the quadrant 30. Exists. A position rp3 at which the magnetic field intensity of the magnetic field distribution 33 becomes a maximum value exists in the region of the outer peripheral thick portion 27 of the pole tip 7a. As shown in FIG. 10, in order to obtain the magnetic field distribution 33 having the minimum value and the maximum value, the regions rp2 of the desired minimum value of the magnetic field distribution 33 are respectively set in the regions of the thin portion 26 and the outer peripheral thick portion 27 of the pole tip 7a. Further, adjustment may be made so as to include the position rp3 of the maximum value of the desired magnetic field distribution 33. Further, by adjusting the thickness of the thin portion 26 of the pole tip 7a, the position rp2 of the minimum value of the desired magnetic field distribution 33 can be adjusted. Similarly, the position rp3 of the maximum value of the desired magnetic field distribution 33 can be adjusted by adjusting the thickness of the outer peripheral thick portion 27 of the pole tip 7a.

The desired minimum position rp2 of the magnetic field distribution 33 can be changed by the arrangement position of the thin portion 26 of the pole tip 7 and the thickness of the thin portion 26. Similarly, the position rp3 of the desired maximum value of the magnetic field distribution 33 can be changed by the arrangement position of the outer peripheral thick portion 27 of the pole tip 7 and the thickness of the outer peripheral thick portion 27. Since the outer peripheral thick portion 27 of the pole tip 7 includes the outer peripheral end, the arrangement position of the outer peripheral thick portion 27 can be rephrased as the radial width of the outer peripheral thick portion 27.

There are two methods for increasing the strength of the magnetic field in the Z direction by the pole tip 7. The first method is to increase the thickness of the pole tip 7. The second method is to bring the pole tip 7 closer to the midplane 12.

Therefore, the desired magnetic field distribution 33 can be obtained by determining the thickness of the pole tip 7 according to the radial position and determining the arrangement position of the pole tip 7. There are an infinite number of cross-sectional shapes of the pole tip 7 forming the desired magnetic field distribution 33. The pole tip 7 of the first example shown in FIGS. 5 to 7 has irregularities on the inward surface 18 and the outward surface 22, and the radial width of the inward flat portion 19 of the inward surface 18 is flat on the outward side of the outward surface 22. This is an example wider than the section 23. Further, the pole tip 7 of the first example is also an example in which the area of the inward flat portion 19 of the inward surface 18 is wider than the outward flat portion 23 of the outward surface 22.

In order to make the magnetic field distribution by the pole tip 7 highly accurate, it is necessary to form the pole tip 7 with high accuracy, but the shape accuracy of the inward surface 18 on the side facing the midplane 12 is the outward surface 22. It is necessary to be higher than the shape accuracy. The pole tip 7 of the first example has a sufficiently high machining accuracy because the area of the inward flat portion 19 in the inward surface 18 on the side facing the midplane 12 is wider than the outward flat portion 23 of the outward surface 22. can do. Therefore, the pole tip 7 of the first example can form the desired magnetic field distribution 33 with high accuracy.

As described above, the pole tip 7 forming one desired magnetic field distribution 33 has an infinite number of cross-sectional shapes, and is not limited to the examples shown in FIGS. 5 to 7, and other pole tips may be used. A second example of the pole tip shown in FIGS. 11 to 13 will be described. The reference numeral of the pole tip of the second example is 34 to distinguish it from the pole tip of the first example. The pole tip 34 of the second example differs from the pole tip 7 of the first example in that there is no inward convex portion 20 on the inward surface 18. The pole tip 34 of the second example shown in FIGS. 11 to 13 shows an example in which the radial position and the radial width of the thin portion 26 are different from those of the pole tip 7 of the first example.

In FIG. 11, the outward-side convex portion 24 is between the broken line A2 and the broken line A3, and the outward-side flat portion 23 is between the broken line A1 and the broken line A2, and between the broken line A3 and the broken line A4. The convex portion 25 is between the broken line A1 and the left end and between the broken line A4 and the right end. In FIG. 11, the inward flat portion 19 is between the broken line B1 and the broken line B2, and the inward outer peripheral convex portion 21 is between the broken line B1 and the left end and between the broken line B2 and the right end. The outer peripheral ends of the pole tip 34 are a left end and a right end of the pole tip 34 in FIG.

Since the pole tip 34 has irregularities on the inward surface 18 and the outward surface 22, the thickness perpendicular to the midplane 12 changes from the center line 28 toward the outer peripheral side. The pole tip 34 is thickest at the left end and the right end. The thickness in the left end direction from the center line 28 decreases from the thickest portion (top) of the outward convex portion 24 through which the center line 28 passes toward the broken line A2, and is thinnest between the broken line A2 and the broken line B1. And thicker towards the left end. Between the broken line A2 and the broken line B1, it is the thin part 26 with the thinnest thickness in the vertical direction. The thickness in the right end direction from the center line 28 decreases from the thickest portion (top) of the outward convex portion 24 through which the center line 28 passes toward the broken line A3, and is thinnest between the broken line A3 and the broken line B2. It becomes thicker toward the right end. Between the broken line A3 and the broken line B2, it is the thin part 26 with the thinnest thickness in the vertical direction. In addition, the left thin part 26 and the right thin part 26 in FIG. 11 are formed concentrically with the center line 28 as the center, like the outward flat part 23 and the like.

The pole tip 34 of the second example has a sufficiently high machining accuracy because the area of the inward flat portion 19 in the inward surface 18 on the side facing the midplane 12 is larger than the outward flat portion 23 of the outward surface 22. can do. Therefore, the pole tip 34 of the second example can form the desired magnetic field distribution 33 with high accuracy. Since the pole tip 34 of the second example does not have the inward-side convex portion 20 on the inward surface 18, the slope at which the magnetic field distribution 33 decreases can be made gentler than that of the pole tip 7 of the first example. The reverse is true for the pole tip 7 of the first example. That is, since the pole tip 7 of the first example has the inward convex portion 20 on the inward surface 18, the magnetic field distribution 33 is reduced compared to the pole tip 34 of the second example in which the inward convex portion 20 is not present on the inward surface 18. The inclination can be made steep.

A third example of the pole tip shown in FIGS. 14 to 16 will be described. The symbol of the pole tip of the third example is set to 35 to distinguish it from the pole tip of the first example and the second example. The pole tip 35 of the third example is different from the pole tip 7 of the first example in that there is no inward convex portion 20 on the inward surface 18 like the pole tip 34 of the second example. Further, the pole tip 35 of the third example shown in FIGS. 14 to 16 is different from the pole tip 7 of the first example in the radial position and radial width of the thin portion 26 as in the pole tip 34 of the second example. An example is shown. The pole tip 35 of the third example is different from the pole tip 34 of the second example in that the thicknesses of the outward-side convex portion 24 and the outward-side outer peripheral convex portion 25 are changed stepwise. 14 to 16, from the outward flat part 23 to the thickest part (top) of the outward convex part 24, and from the outward flat part 23 to the thickest part (top) of the outward peripheral convex part 25. An example is shown in which the wall thickness changes stepwise due to three flat portions.

In FIG. 14, the outward convex part 24 is between the broken line A2 and the broken line A3, and the outward flat part 23 is between the broken line A1 and the broken line A2 and between the broken line A3 and the broken line A4. The convex portion 25 is between the broken line A1 and the left end and between the broken line A4 and the right end. In FIG. 14, the inward flat portion 19 is between the broken line B1 and the broken line B2, and the inward outer peripheral convex portion 21 is between the broken line B1 and the left end and between the broken line B2 and the right end. The outer peripheral ends of the pole tip 35 are a left end and a right end of the pole tip 35 in FIG.

Since the pole tip 35 has irregularities on the inward surface 18 and the outward surface 22, the thickness in the direction perpendicular to the midplane 12 changes from the center line 28 toward the outer peripheral side. The pole tip 35 is thickest at the left end and the right end. The thickness in the left end direction from the center line 28 decreases from the thickest portion (top) of the outward convex portion 24 through which the center line 28 passes toward the broken line A2, and is thinnest between the broken line A2 and the broken line B1. And thicker towards the left end. Between the broken line A2 and the broken line B1, it is the thin part 26 with the thinnest thickness in the vertical direction. The thickness in the right end direction from the center line 28 decreases from the thickest portion (top) of the outward convex portion 24 through which the center line 28 passes toward the broken line A3, and is thinnest between the broken line A3 and the broken line B2. It becomes thicker toward the right end. Between the broken line A3 and the broken line B2, it is the thin part 26 with the thinnest thickness in the vertical direction. Note that the left thin portion 26 and the right thin portion 26 in FIG. 14 are formed concentrically around the center line 28 as in the case of the outward flat portion 23 and the like.

The pole tip 35 of the third example has a sufficiently high machining accuracy because the area of the inward flat portion 19 in the inward surface 18 on the side facing the midplane 12 is wider than the outward flat portion 23 of the outward surface 22. can do. Further, in the pole tip 35 of the third example, since the thicknesses of the outward-side convex portion 24 and the outward-side outer peripheral convex portion 25 are changed stepwise, the processing of the outward surface 22 is easy, and the pole tip is formed. Cost can be reduced. Therefore, the pole tip 35 of the third example can form the desired magnetic field distribution 33 with sufficient accuracy while reducing the production cost. The pole tip 35 of the third example is inferior in formation accuracy of the desired magnetic field distribution 33 compared to the pole tip 7 of the first example. However, the desired magnetic field distribution 33 can be formed with sufficient accuracy, that is, with high accuracy. it can. Since the pole tip 35 of the third example does not have the inward-side convex portion 20 on the inward surface 18, the slope at which the magnetic field distribution 33 decreases can be made gentler than that of the pole tip 7 of the first example.

A fourth example of the pole tip shown in FIGS. 17 to 19 will be described. The sign of the pole tip of the fourth example is set to 36 to distinguish it from the pole tip of the first example to the third example. The pole tip 36 of the fourth example differs from the pole tip 7 of the first example in that the thickness and arrangement position of the inward convex portion 20 on the inward surface 18 are the same as the outward convex portion 24 of the outward surface 22. The pole tip 36 of the fourth example shown in FIGS. 17 to 19 shows an example in which the cross-sectional shape of the inward surface 18 and the cross-sectional shape of the outward surface 22 are the same.

In FIG. 17, the outward convex part 24 is between the broken line A2 and the broken line A3, and the outward flat part 23 is between the broken line A1 and the broken line A2 and between the broken line A3 and the broken line A4. The convex portion 25 is between the broken line A1 and the left end and between the broken line A4 and the right end. In FIG. 17, the inward convex portion 20 is between the broken line B2 and the broken line B3, and the inward side flat portion 19 is between the broken line B1 and the broken line B2 and between the broken line B3 and the broken line B4. The side outer peripheral convex portion 21 is between the broken line B1 and the left end and between the broken line B4 and the right end.

Since the pole tip 36 has irregularities on the inward surface 18 and the outward surface 22, the thickness in the direction perpendicular to the midplane 12 changes from the center line 28 toward the outer peripheral side. As for the thickness of the pole tip 36, the thickest part (top) of the outward convex part 24 through which the center line 28 passes and the thickest part of the inward peripheral convex part 21 are the thickest. The thickness in the left end direction from the center line 28 decreases toward the broken lines A2 and B2 from the thickest portions of the outward convex portion 24 and the inward outer peripheral convex portion 21 through which the central line 28 passes, and from the broken lines A2 and B2. The distance between the broken lines A1 and B1 is the thinnest and thicker toward the left end. Between the broken lines A2 and B2 and the broken lines A1 and B1, the thin portion 26 is the thinnest in the vertical direction. The thickness in the right end direction from the center line 28 decreases from the thickest portions of the outward convex portion 24 and the inward outer peripheral convex portion 21 through which the central line 28 passes toward the broken lines A3 and B3, and from the broken lines A3 and B3. The portion between the broken lines A4 and B4 is the thinnest and thicker toward the right end. Between the broken lines A3 and B3 and the broken lines A4 and B4 is the thin portion 26 having the smallest thickness in the vertical direction. In addition, the thin part 26 on the left side and the thin part 26 on the right side in FIG. 17 are formed concentrically with the center line 28 as the center, similarly to the outward flat part 23 and the inward flat part 19.

In the pole tip 36 of the fourth example, the cross-sectional shape of the inward surface 18 and the cross-sectional shape of the outward surface 22 are the same, so the processing of the inward surface 18 and the processing of the outward surface 22 can be made the same. Therefore, it is possible to reduce the production cost of the pole tip.

The particle beam circular accelerator 51 of the first embodiment includes

superconducting coils

3a and 3b that are air-core coils (air-core coils), and a pair of

pole tips

7a and 7b (a pair of

superconducting coils

3a and 3b). The

pole tips

34, 34, 35, 35, 36, and 36) are provided, so that the weight can be reduced compared to an accelerator having a yoke as in Patent Document 2. Since the particle beam circular accelerator 51 of the first embodiment is light in weight, it can be mounted on a rotating gantry that is smaller than the conventional one.

If the synchrocyclotron equipped with a yoke is simply reduced in weight, the number of emitted charged particles can be reduced. On the other hand, the particle beam circular accelerator 51 according to the first embodiment includes

superconducting coils

3a and 3b that are air-core coils (air-core type coils) and a pair of

pole tips

7a and 7b (a pair) disposed inside them. The

pole tips

34, 34, 35, 35, 36, 36) are provided, so that a sufficient Z-direction magnetic field can be generated while being lightweight, and sufficient charged particles equivalent to the conventional one can be emitted. it can.

Since the particle beam irradiation apparatus 59 of Embodiment 1 can mount the light particle beam circular accelerator 51 in the rotating gantry 60 compared with the accelerator provided with the yoke like patent document 2, the rotating gantry 60 can be reduced in size. it can. Moreover, since the particle beam irradiation apparatus 59 of Embodiment 1 can make the rotating gantry 60 small, a particle beam irradiation apparatus can be reduced in size. Moreover, since the particle beam irradiation apparatus 59 of Embodiment 1 can be made smaller than before, the installation area in which the particle beam irradiation apparatus is installed can be reduced, and the particle beam irradiation apparatus and the particle beam irradiation apparatus are installed. The cost of the building can be reduced.

As described above, the particle beam irradiation apparatus 59 of the first embodiment generates the charged particle beam 16 and accelerates it while rotating it with a magnetic field, and the charged particles accelerated by the particle beam circular accelerator 51. A beam transport system 54 that transports the beam 16, an irradiation field forming device 56 that irradiates the irradiation target (patient 58) with the charged particle beam 16 transported by the beam transport system 54, a particle beam circular accelerator 51, and a beam transport system 54. The particle beam irradiation apparatus includes a rotating gantry 60 that supports the irradiation field forming apparatus 56 and rotates the irradiation direction of the charged particle beam 16. The particle beam circular accelerator 51 includes an acceleration cavity 11 for accelerating the charged particle beam 16, a pair of

superconducting coils

3a and 3b arranged symmetrically with respect to the acceleration orbit plane (midplane 12) of the charged particle beam 16, and superconductivity. Arranged inside the

coils

3a and 3b and symmetrically with respect to the acceleration orbit plane (midplane 12), the charged particle beam 16 circulates in the acceleration cavity 11 from the magnetic field generated by the

superconducting coils

3a and 3b. A pair of

pole tips

7a and 7b for forming a magnetic field distribution is provided. The

pole tips

7a and 7b of the particle beam irradiation device 59 have a radial thickness in the radial direction, which is the thickness of the inward surface 18 facing the acceleration track surface (midplane 12) and the outward surface 22 farther away from the inward surface 18. A central portion (inward convex portion 20 and outward convex portion 24) that includes a coil shaft 17 that is perpendicular to the radial direction of the

superconducting coils

3a and 3b and passes through the centers of the

superconducting coils

3a and 3b, and a radially outer periphery. The inner part (inward-side outer convex part 21, outward-side outer convex part 25), the central part (inward-side convex part 20, outward-side convex part 24) and the outer peripheral part (inward-side outer convex part 21, outward-side outer convex part) The thin portion 26 is thinner than the portion 25) and has the smallest thin portion 26. The thin portion 26 has a region that is more than half of the radially arranged region, the coil shaft 17 and the outer peripheral ends of the

pole tips

7a and 7b. So that it is on the outer peripheral side of the intermediate line 29 Characterized in that the location. Due to this feature, the particle beam irradiation apparatus 59 of the first embodiment includes a pair of

superconducting coils

3a and 3b and a pair of

pole tips

7a and 7b arranged inside the

superconducting coils

3a and 3b. Since the thin portions 26 of the

pole tips

7a and 7b are arranged so as to be more than half on the outer peripheral side of the intermediate line 29 between the coil shaft 17 and the outer peripheral ends of the

pole tips

7a and 7b, a lightweight accelerator A certain particle beam circular accelerator 51 can be mounted on the rotating gantry 60, and the particle beam irradiation apparatus can be reduced in size.

Embodiment 2. FIG.
FIG. 20 is a cross-sectional view showing a schematic configuration of the particle beam circular accelerator according to the second embodiment of the present invention. 21 is a bird's-eye view of the fixed structure and the pole tip shown in FIG. 20, and FIG. 22 is a cross-sectional view showing a first example of the pole tip shown in FIG. 20 and a superconducting coil. 23 is a cross-sectional view showing a first example of the pole tip of FIG. 24 is a diagram showing the inward surface of the pole tip in FIG. 23, and FIG. 25 is a diagram showing the outward surface of the pole tip in FIG. FIG. 26 is an enlarged view of the pole tip of FIG. FIG. 27 is a cross-sectional view showing a second example of the pole tip of FIG. 28 is a bird's-eye view of the pole tip shown in FIG. 27, and FIG. 29 is a diagram showing an inward surface of the pole tip shown in FIG. 30 is a cross-sectional view showing a third example of the pole tip of FIG. 31 is a bird's-eye view of the pole tip shown in FIG. 30, and FIG. 32 is a view showing an outward surface of the pole tip shown in FIG.

The particle beam circular accelerator 51 of the second embodiment is different from the particle beam circular accelerator 51 of the first embodiment in that the outward surface 22 or the inward surface 18 includes

pole tips

37a and 37b that are flat. The reference numeral of the pole tip is generally 37, and 37a and 37b are used in the case of distinction. The pole tip 37 is an example in which the outward surface 22 is flat. The pole tip 37 has a cross-sectional shape in which the thickness that is the thickness of the inward surface 18 and the outward surface 22 changes from the center line 28 toward the outer peripheral side. A pole tip 37, which is a first example of the pole tip shown in FIGS. 23 to 26, is an example in which the outward face 22 is flat and the inward face 18 is uneven. As shown in FIGS. 24 and 25, the pole tip 37 has a circular outer periphery on the outward face 22 and the inward face 18. Further, the pole tip 37 is thickened by a plurality of flat portions from the inward-side outer peripheral convex portion 21 positioned on the left outer peripheral end side to the inward-side outer peripheral convex portion 21 positioned on the right outer peripheral end side in FIG. An example of a step-like change is shown. As shown in the enlarged view of FIG. 26, each of the plurality of flat portions is a narrow flat portion 40 having a narrow radial width. In FIG. 26,

reference numerals

40a, 40b, 40c, 40d, 40e, 40f, 40g, and 40h are given to distinguish some narrow flat portions. The broken line BB is the broken line B2 or the broken line B3. In the case of the inward-side outer peripheral convex portion 21 located on the left outer peripheral end side, the broken line BB represents the broken line B2, and the inwardly located on the right outer peripheral end side. In the case of the side outer periphery convex part 21, the broken line BB represents the broken line B3.

The change in the thickness of the pole tip 37 will be described using broken lines B1, B2, B3, and B4 parallel to the center line 28. Since the pole tip 37 has irregularities on the inward surface 18, the thickness in the direction perpendicular to the midplane 12 changes from the center line 28 toward the outer peripheral side. Between the left outer peripheral edge and the broken line B1 and between the broken line B4 and the right outer peripheral edge is the inward-side outer peripheral convex part 21, and this inward-side outer peripheral convex part 21 has the thickest thickness. That is, the pole tip 37 is thickest at the left end and the right end. The thickness in the direction of the left end from the center line 28 decreases from the center part through which the center line 28 passes toward the broken line B2, and the narrow flat part 40f on the outer peripheral side from the broken line B2 is the thinnest region. The thickness increases from the flat portion 40f toward the left end. The thickness in the right end direction from the center line 28 decreases from the central portion through which the center line 28 passes toward the broken line B3, and the narrow flat portion (narrow flat portion 40f) on the outer peripheral side from the broken line B3 is the thinnest region. It is thicker from the narrow flat part (narrow flat part 40f) toward the left end. The region of the narrow flat portion 40f having the smallest thickness corresponds to the thin portion 26 described in the first embodiment. This thin portion 26 is shown in FIG. The thickness of the pole tip 37 in the region of the narrow flat portion 40f is the thickness t1. The central portion through which the center line 28 passes is the summit where the central portion is higher than the periphery if FIG. 23 is turned upside down. Therefore, it can be said that the central portion through which the center line 28 passes is the upper part of the reverse apex. In other drawings, if a certain part is higher than the periphery and is on the top if it is turned upside down, that part is appropriately referred to as the inverted top.

FIG. 22 shows the radial positions of the thin-walled portion 26 with the smallest thickness and the outer-walled thick portion 27 with the thickest thickness. In FIG. 22, the pole tip 37a and the superconducting coil 3a are shown, but the thin portion 26 and the outer peripheral thick portion 27 of the pole tip 37b are also at the same radial position. In FIG. 22, the horizontal axis is the radial position R from the center line 28, and the vertical axis is the position in the center line 28 direction, that is, the position Z in the Z direction. The center line 28 has a radial position R of zero, the right outer peripheral edge is r1, and the left outer peripheral edge is -r1. The intermediate line 29 is an intermediate line between the center line 28 and the outer peripheral end of the pole tip 37. Intermediate line 29 is at r1 / 2 and -r1 / 2. In FIG. 22, between the broken line C <b> 5 and the broken line C <b> 6 is the inward-side outer peripheral convex portion 21 (see FIG. 23) and the outer peripheral thick portion 27. Between the broken line C7 and the broken line C8 is an inward-side outer peripheral convex portion 21 (see FIG. 23), and both are outer peripheral thick portions 27. If the thin portion 26 is at least on the outer peripheral side in the radial direction by r1 / 2 or -r1 / 2, the pole tip 37 (37a, 37b) has a minimum and maximum magnetic field strength on the outer peripheral side as shown in FIG. A magnetic field distribution 33 having a value can be generated. In FIG. 22, in order to distinguish the right side and the left side of the pole tip 37a, the description has been made using the positive and negative positions of the radial position R. However, the pole tip 37 is centered on the center line 28. Because of the concentric shape, it can be said that the thin portion 26 has a radial position from the center line 28 on the outer peripheral side from r1 / 2.

In the pole tip 37 of the first example of the second embodiment, the outward face 22 is flat and the wall thickness is changed stepwise. Therefore, the processing of the outward face 22 and the inward face 18 is easy. The production cost can be reduced. Further, since the pole tip 37 can be finely changed in thickness using a large number of narrow flat portions, a complicated shape can be realized while reducing the production cost.

As described in the first embodiment, the pole tip that forms one desired magnetic field distribution 33 has an infinite number of cross-sectional shapes. Therefore, the pole tip with the outward face 22 or the inward face 18 being flat is not limited to the pole tip 37. Other pole tips may be used. A second example of the pole tip according to the second embodiment shown in FIGS. 27 to 29 will be described. The reference number of the pole tip of the second example is 38 in order to distinguish it from the first example to the fourth example pole tip of the first embodiment and the pole tip of the first example of the second embodiment. The pole tip 38 of the second example is the first example in that the inward surface 18 includes the inward convex portion 20, the inward flat portion 19, and the inward outer peripheral convex portion 21 without using the plurality of narrow flat portions 40. Different from the pole tip 37.

In FIG. 27, the inward convex portion 20 is between the broken line B2 and the broken line B3, and the inward side flat portion 19 is between the broken line B1 and the broken line B2 and between the broken line B3 and the broken line B4. The convex portion 21 is between the broken line B1 and the left end and between the broken line B4 and the right end. The intermediate line 29 is an intermediate line between the center line 28 and the outer peripheral end of the pole tip 38. The outer peripheral ends of the pole tip 38 are a left end and a right end of the pole tip 38 in FIG.

Since the pole tip 38 has irregularities on the inward surface 18, the thickness in the direction perpendicular to the midplane 12 changes from the center line 28 toward the outer peripheral side. As for the thickness of the pole tip 38, the thickest portion (inverted top) of the inward convex portion 20 through which the center line 28 passes is the thickest. The thickness in the direction of the left end from the center line 28 decreases from the thickest part (the reverse top) of the inward-side outer peripheral convex part 21 through which the center line 28 passes from the broken line B2 to the broken line B1. It is the thinnest and thicker toward the left end. Between the broken line B2 and the broken line B1, it is the thin part 26 with the thinnest thickness in the vertical direction. The thickness in the right end direction from the center line 28 decreases toward the broken line B3 from the thickest part (upper top part) of the inward-side outer peripheral convex part 21 through which the center line 28 passes, and between the broken line B3 and the broken line B4. It is the thinnest and thicker toward the right end. Between the broken line B3 and the broken line B4 is the thin portion 26 having the smallest thickness in the vertical direction. Note that the left thin portion 26 and the right thin portion 26 in FIG. 27 are formed concentrically around the center line 28, as in the inward flat portion 19.

Since the pole tip 38 of the second example has a flat outward surface 22, the pole tip can be easily processed, and the cost for creating the pole tip can be reduced.

A third example of the pole tip according to the second embodiment shown in FIGS. 30 to 31 will be described. The reference number of the pole tip of the third example is set to 39 to distinguish it from the first example to the fourth example pole tip of the first embodiment, the first example of the second embodiment, and the second example pole tip. The pole tip 39 of the third example differs from the pole tip 38 of the second example in that the inward surface 18 is flat and includes an outward-side convex portion 24, an outward-side flat portion 23, and an outward-side outer peripheral convex portion 25.

Since the pole tip 39 has irregularities on the outward surface 22, the thickness in the direction perpendicular to the midplane 12 changes from the center line 28 toward the outer peripheral side. The pole tip 39 is thickest at the thickest portion (top) of the outward convex portion 24 through which the center line 28 passes. The thickness in the left end direction from the center line 28 decreases from the thickest portion (top) of the outward convex portion 24 through which the center line 28 passes toward the broken line A2, and is thinnest between the broken line A2 and the broken line A1. And thicker towards the left end. Between the broken line A2 and the broken line A1, it is the thin part 26 with the thinnest thickness in the vertical direction. The thickness in the right end direction from the center line 28 decreases from the thickest portion (top) of the outward convex portion 24 through which the center line 28 passes toward the broken line A3, and is thinnest between the broken line A3 and the broken line A4. It becomes thicker toward the right end. Between the broken line A3 and the broken line A4 is the thin part 26 with the smallest thickness in the vertical direction. In addition, the thin part 26 on the left side and the thin part 26 on the right side in FIG. 30 are formed concentrically with the center line 28 as the center, similarly to the outward flat part 23.

The pole tip 39 of the third example has a flat inward surface 18 so that the pole tip can be easily processed and the cost for producing the pole tip can be reduced. Further, in the pole tip 39 of the third example, since the area of the inward surface 18 on the side facing the midplane 12 is wider than the outward flat portion 23 of the outward surface 22, the machining accuracy can be sufficiently increased. . Therefore, the pole tip 39 of the third example can form the desired one magnetic field distribution 33 with higher accuracy than the pole tip 38 of the second example.

The particle beam circular accelerator 51 of the second embodiment includes

superconducting coils

3a and 3b that are air-core coils (air-core coils), and a pair of

pole tips

37a and 37b (a pair of

superconducting coils

3a and 3b). The

pole tips

38, 38, 39, 39) are provided, so that the weight can be reduced as compared with an accelerator having a yoke as in Patent Document 2. Since the particle beam circular accelerator 51 of the second embodiment is light in weight, it can be mounted on a rotating gantry that is smaller than the conventional one.

The particle beam irradiation apparatus 59 according to the second embodiment in which the particle beam circular accelerator 51 according to the second embodiment is mounted on the rotating gantry 60 is a light particle beam circular accelerator that is lighter than an accelerator having a yoke as in Patent Document 2. Since 51 is mounted on the rotating gantry 60, the rotating gantry 60 can be reduced in size. In the particle beam irradiation apparatus 59 of the second embodiment, since the rotating gantry 60 can be reduced in size, the particle beam irradiation apparatus can be reduced in size. Moreover, since the particle beam irradiation apparatus 59 of Embodiment 2 can be made smaller than before, the installation area in which the particle beam irradiation apparatus is installed can be reduced, and the particle beam irradiation apparatus and the particle beam irradiation apparatus are installed. The cost of the building can be reduced.

It should be noted that the present invention can be combined with each other within the scope of the invention, and each embodiment can be modified or omitted as appropriate.

3a, 3b ... superconducting coil, 7, 7a, 7b ... pole tip, 11 ... acceleration cavity, 12 ... midplane, 16 ... charged particle beam, 17 ... coil axis, 18 ... inward surface, 19 ... inward flat portion, 20 ... inward convex part, 21 ... inward peripheral convex part, 22 ... outward surface, 23 ... outward flat part, 24 ... outward convex part, 25 ... outward peripheral convex part, 26 ... thin part, 28 ... center line , 29 ... Intermediate line, 34, 35, 36, 37, 37a, 37b ... Pole tip, 51 ... Particle beam circular accelerator, 54 ... Beam transport system, 56 ... Irradiation field forming device, 58 ... Patient, 59 ... Particle beam irradiation Equipment, 60 ... rotating gantry

Claims

A particle beam circular accelerator that generates a charged particle beam and accelerates it while rotating by a magnetic field, a beam transport system that transports the charged particle beam accelerated by the particle beam circular accelerator, and the transported by the beam transport system An irradiation field forming apparatus that irradiates a charged particle beam to an irradiation target, and a rotating gantry that supports the particle beam circular accelerator, the beam transport system, and the irradiation field forming apparatus and that rotates the irradiation direction of the charged particle beam. A particle beam irradiation device,
The particle beam circular accelerator is
An acceleration cavity for accelerating the charged particle beam;
A pair of superconducting coils arranged symmetrically with respect to the acceleration orbital plane of the charged particle beam;
Arranged inside the superconducting coil, symmetrically arranged with respect to the acceleration orbital plane, and forming a magnetic field distribution that circulates the charged particle beam in the acceleration cavity from the magnetic field generated by the superconducting coil; With a pair of pole tips,
The pole tip is
The thickness which is the thickness of the inward surface facing the acceleration orbital surface and the outward surface farther away from the inward surface is different in the radial direction,
Inside the central portion and the outer peripheral portion in the radial direction that includes the coil axis perpendicular to the radial direction of the superconducting coil and passing through the center of the superconducting coil, the thickness is smaller than the central portion and the outer peripheral portion, and the minimum With a thin part of
Particles characterized in that the thin portion is arranged such that more than half of the radial arrangement region is on the outer peripheral side of the intermediate line between the coil shaft and the outer peripheral end of the pole tip X-ray irradiation device.
The pole tip includes, on the outward face, an outwardly flat part closest to the inward face, and an outwardly facing convex part projecting from the outwardly flat part in the direction of the coil axis and away from the inward face. Have
The thin portion is included in a region of the outward flat portion,
The particle beam irradiation apparatus according to claim 1, wherein an area of the outward flat portion is smaller than an area of the flat portion on the inward surface.
The pole tip has an inward flat portion closest to the outward surface on the inward surface, and a convex portion on the inward surface side protruding from the inward flat portion in the direction of the coil axis and away from the outward surface. Have
The thin portion is included in a region of the inward flat portion,
The particle beam irradiation apparatus according to claim 2, wherein an area of the outward flat portion is smaller than an area of the inward flat portion.
3. The particle beam irradiation apparatus according to claim 2, wherein the inward surface of the pole tip is flat.
The pole tip is
In the outward surface, it has an outward flat portion closest to the inward surface, and an outward surface convex portion protruding from the outward flat portion in the direction of the coil axis and away from the inward surface,
In the inward surface, it has an inward flat portion closest to the outward surface, and a convex portion on the inward surface side that protrudes from the inward flat portion in the direction of the coil axis and away from the outward surface,
The boundary between the outward flat portion and the convex portion on the outward surface side is the same radial position as the boundary between the inward flat portion and the convex portion on the inward surface side,
The particle beam irradiation apparatus according to claim 1, wherein the thin portion is included in a region of the outward flat portion and the inward flat portion.
The particle beam irradiation apparatus according to any one of claims 2 to 4, wherein the thickness of the convex portion on the outward surface side in the outward surface changes in a stepped manner.
6. The particle beam irradiation apparatus according to claim 5, wherein the thickness of the convex portion on the outward surface side in the outward surface and the convex portion on the inward surface side in the inward surface are changed in a stepped manner. .
The pole tip has a flat outward surface,
In the inward surface, it has an inward flat portion closest to the outward surface, and a convex portion on the inward surface side that protrudes from the inward flat portion in the direction of the coil axis and away from the outward surface,
The thin portion is included in a region of the inward flat portion,
The particle beam irradiation apparatus according to claim 1, wherein the thickness of the convex portion on the inward surface side changes in a stepped manner.
The pole tip has a flat outward surface,
In the inward surface, it has an inward flat portion closest to the outward surface, and a convex portion on the inward surface side that protrudes from the inward flat portion in the direction of the coil axis and away from the outward surface,
The particle beam irradiation apparatus according to claim 1, wherein the thin portion is included in a region of the inward flat portion.