Accelerator and particle therapy system

Patent metadata

Field	Value
Publication number	US-12382573-B2
Application number	US-202118276094-A
Country	US
Kind code	B2
Filing date	Dec 23, 2021
Priority date	Feb 8, 2021
Publication date	Aug 5, 2025
Grant date	Aug 5, 2025

Abstract

As the ion beam is accelerated, the radii of the closed orbits gradually increase, and the centers thereof move in a direction approaching the peripheral edge portion along a predetermined radial direction of the cavity, and upon reversing the direction of movement, move further toward the center of the cavity. The intensity distribution in the orbital plane of the main magnetic field is designed to realize the foregoing feature. Thus, an accelerator is provided that is compact and that enables the energy of an extracted beam to be changed, that enhances the efficiency of beam injection into the accelerator from an external ion source, and that improves a dose rate of the resulting extracted ion beam.

First claim

The invention claimed is:

1. An accelerator comprising:
an electromagnet that includes a pair of magnetic poles arranged opposite each other having an orbital plane for circulating an ion beam interposed therebetween and that forms a main magnetic field that generates a plurality of closed orbits on the orbital plane;
an ion injection through-hole formed in the magnetic pole in order to externally introduce an ion beam to a predetermined injection position on the orbital plane;
a radiofrequency acceleration cavity that is inserted into a cavity formed between the pair of magnetic poles and that generates a radio frequency for accelerating the ion beam circulating in the orbital plane;
an additional magnetic field generator that is disposed on an outer periphery of the cavity, that feeds a magnetic field to the moving ion beam on one or more closed orbits of an outermost periphery and inside the outermost periphery such that the direction of movement of the ion beam is made to deviate from the closed orbits; and
an extraction channel that guides the ion beam which has deviated from the closed orbits, to an outside of the cavity,
wherein an intensity distribution in the orbital plane of the main magnetic field is designed such that, as the ion beam is accelerated, the radii of the closed orbits gradually increase, and the centers thereof move in a direction approaching the peripheral edge portion along a predetermined radial direction of the cavity, and upon reversing the direction of movement, move further toward the center of the cavity.

2. The accelerator according to claim 1 , wherein the intensity distribution of the main magnetic field of the electromagnet is designed such that, until the radii of the closed orbits reach a predetermined first radius, the centers thereof move in a direction approaching a peripheral edge portion of the cavity along the predetermined radial direction of the cavity, and after reaching the first radius, move toward the center of the cavity along the radial direction.

3. The accelerator according to claim 1 , wherein
each of the pair of magnetic poles has a cylindrical shape and includes magnetic pole surfaces arranged symmetrically and having the orbital plane interposed therebetween, and
the ion injection through-hole is provided in a position where a central axis thereof is perpendicular to the orbital plane and orthogonal to the predetermined radial direction.

4. The accelerator according to claim 1 , wherein a distance between a central axis of the ion injection through-hole and the center of the cavity is provided within 50% of a radial length of the cavity.

5. The accelerator according to claim 3 , wherein shims are arranged on the magnetic pole surfaces in positions between the ion injection through-hole and the center of the magnetic pole and adjacent to the ion injection through-hole.

6. The accelerator according to claim 5 , wherein
the ion injection through-hole and the shims are each provided in symmetrical positions to the opposing magnetic poles and having the orbital plane interposed therebetween, and
a distance between a pair of shims is narrower than a distance between the pair of magnetic pole surfaces in positions along the predetermined radial direction between the ion injection through-hole and an outer periphery of the magnetic pole surface and adjacent to the ion injection through-hole, or a distance between shims arranged in those positions.

7. The accelerator according to claim 1 , wherein an ion source that causes an ion beam to be injected into the ion injection through-hole is installed outside the electromagnet.

8. The accelerator according to claim 1 , wherein the extraction channel is disposed on an outer periphery of the cavity in the predetermined radial direction.

9. The accelerator according to claim 5 , wherein a magnetic field gradient in each position, along the radial direction, between the ion injection through-hole and the center of the magnetic pole is greatest in the position where the shims are arranged.

10. The accelerator according to claim 9 , wherein a magnetic field gradient in each position, along the radial direction, between the ion injection through-hole and the outer periphery of the cavity is greatest in the peripheral edge portion of the cavity.

11. The accelerator according to claim 3 , wherein the magnetic pole surfaces are provided with a plurality of ring-shaped trim coils, and the trim coils have a radius corresponding to the plurality of closed orbits of the orbital plane, and are provided on the magnetic pole surfaces in positions corresponding to the closed orbits.

12. The accelerator according to claim 1 , wherein the radiofrequency acceleration cavity includes a dee electrode, the edge of the dee electrode is arranged so as to cross the cavity in parallel with the orbital plane, and the shape of the edge is a W-shape centered near the injection position.

13. A particle therapy system with which a patient is irradiated with a particle beam, wherein the accelerator according to claim 1 is used as a device for generating the particle beam.

Assignees

• Hitachi High Tech Corp

Inventors

• Aoki Takamichi
• Seki Takayoshi
• NAKASHIMA Yuto

Classifications

• H05H2277/11

  Radiotherapy · CPC title

• A61N2005/1087

  Ions; Protons · CPC title

• A61N2005/0626

  Monitoring, verifying, controlling systems and methods · CPC title

• A61N5/1077

  Beam delivery systems · CPC title

• A61N5/103

  Treatment planning systems · CPC title