Circular accelerator and particle beam treatment system

Abstract

To provide a circular accelerator and a particle beam treatment system that can apply a large and high-quality beam and are low-cost.SOLUTION: A circular accelerator 1 accelerates a beam of charge particles rotating in a magnetic field so that the closed orbit of the energy of the beam becomes eccentric. The circular accelerator includes: a beam drawing port for drawing out beams with different energies from a closed orbit; a first deflection electromagnet 21 and a second deflection electromagnet 22 for deflecting a beam drawn out of the beam drawing port; and a controller 40a for controlling the amount of excitation of the first and second deflection electromagnets according to the energy of the drawn-out beam. The controller 40a deflects the beam by exciting the first deflection electromagnet 21 and the second electromagnet 22 if the drawn-out beam has the largest energy of the designed circular accelerator.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a circular accelerator for accelerating a particle beam and a particle beam therapy system.

Background Art

[0002] As an example of a technique for precisely controlling the emission of a charged particle beam from a circular accelerator that accelerates a charged particle beam while increasing the orbital radius by applying a high frequency in a main magnetic field, Patent Document 1 describes that in a circular accelerator that accelerates a charged particle beam while increasing the orbital radius by applying a high frequency in a main magnetic field, a high frequency having a different frequency from the high frequency used for acceleration is applied to the charged particle beam to emit the charged particle beam.

[0003] As an example of a particle beam therapy apparatus that can shorten the adjustment time of a particle accelerator, reduce the number of types of operation parameter files, significantly reduce the moving sound of a range shifter and the energy change time, and has a low frequency of system stops due to equipment fluctuations of the particle accelerator, and has small fluctuations in the energy and intensity of a charged particle beam, Patent Document 2 describes that the thickness in the direction in which a charged particle beam passes is different in one direction orthogonal to the beam transmission direction, and a range shifter in which the energy of the transmitted charged particle beam decreases by an amount proportional to the thickness, an upstream-side deflection electromagnet pair that translates the orbit of the charged particle beam in a direction in which the thickness changes parallel to the upstream side of the range shifter in order to transmit the charged particle beam to different portions of the thickness of the range shifter, a downstream-side deflection electromagnet pair that translates the orbit of the charged particle beam transmitted through the range shifter parallel to the extension line of the orbit when it enters the upstream-side deflection electromagnet pair, and a change control device that controls the upstream-side deflection electromagnet pair and the downstream-side deflection electromagnet pair so that the charged particle beam travels along an orbit in which the energy of the charged particle beam decreases to a desired value by passing through the range shifter.

Prior Art Documents

Patent Documents

[0004] Patent Document 1 Japanese Patent Application Laid-Open No. 2019-133745 Patent Document 2 Japanese Patent No. 4115468 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] Particle beam therapy is performed in which a charged particle beam (hereinafter simply referred to as a beam) is accelerated by an accelerator such as a synchrotron or a cyclotron, and the accelerated beam is irradiated onto a lesion such as cancer.

[0006] As one type of accelerator used for particle beam therapy, for example, there is an accelerator as described in Patent Document 1. In the circular accelerator described in Patent Document 1, a circular closed orbit (hereinafter referred to as a central orbit) formed by beam particles having different kinetic energies (hereinafter simply referred to as energies) in a static magnetic field is arranged so as to be eccentric toward the beam extraction port from the accelerator, and beams having different energies are extracted from the same beam extraction port to the outside of the accelerator.

[0007] In the circular accelerator described in Patent Document 1, after accelerating the beam (hereinafter referred to as a circulating beam) orbiting in the accelerator to a desired energy, a high-frequency voltage in a direction (hereinafter referred to as a horizontal direction) perpendicular to the beam traveling direction and the magnetic pole gap direction (hereinafter referred to as the vertical direction) is applied to the circulating beam. The beam particles to which the high-frequency voltage is applied gradually increase the amplitude of the horizontal direction of the vibration (hereinafter referred to as betatron vibration) centered on the central orbit, and come into contact with a magnetic field distribution for generating resonance of the betatron vibration called a peeler magnetic field and a regenerator magnetic field formed around the central orbit. The beam particles that have come into contact with the peeler magnetic field and the regenerator magnetic field rapidly increase the amplitude of the horizontal betatron vibration and enter the extraction septum coil. The septum coil deflects the beam in the outer peripheral direction of the circular accelerator. The deflected beam is extracted to a high-energy beam transport system outside the circular accelerator.

[0008] Therefore, although the circular accelerator described in Patent Document 1 is a circular accelerator that accelerates a beam in a static magnetic field, it is possible to switch the energy of the beam extracted from the circular accelerator within a predetermined range (for example, in the range from 70 MeV to 230 MeV).

[0009] On the other hand, in the circular accelerator described in Patent Document 1, since the septum coil is installed in a limited space within the magnetic pole of the circular accelerator, the intensity of the magnetic field (septum magnetic field) generated by the septum coil is limited. Since the septum coil has a function of aligning the orbits of beams with different energies at the extraction port of the circular accelerator, in the circular accelerator described in Patent Document 1, the orbit of the beam extracted from the circular accelerator may change with the change in energy due to the lack of the septum magnetic field.

[0010] Here, devices such as deflection electromagnets and quadrupole electromagnets that make up the high-energy beam transport system need to be manufactured so as to enclose the beam orbits of all energies passing through the high-energy beam transport system.

[0011] For this reason, in the circular accelerator described in Patent Document 1, in order to cope with the change in the extraction beam orbit, the component devices of the high-energy beam transport system are enlarged, and there is room for improvement because the installation area and cost of the accelerator system composed of the high-energy beam transport system, the circular accelerator, and the beam transport system may increase.

[0012] The energy changing device described in Patent Document 2 is composed of an energy absorber (range shifter) with different thicknesses depending on the location in a plane perpendicular to the beam orbit, two deflection electromagnets installed upstream of the range shifter, and two deflection electromagnets installed downstream of the range shifter.

[0013] In the energy conversion device described in Patent Document 2, the position where the beam extracted from the accelerator enters the range shifter, that is, the thickness of the range shifter, is controlled by deflecting the beam with an upstream deflection electromagnet, and the energy of the beam after passing through the range shifter is changed to a desired value. The beam that has passed through the range shifter is deflected by a downstream deflection electromagnet and aligned on the extension of the beam orbit before entering the energy conversion device. As a result, the energy conversion device described in Patent Document 2 can adjust the energy of the beam to a desired value without changing the orbit of the beam, so that the energy of the beam extracted from a static magnetic field type accelerator such as a cyclotron can be adjusted and used for applications such as particle beam therapy.

[0014] On the other hand, since the energy conversion device described in Patent Document 2 uses a range shifter for energy conversion, there is a risk that the spatial spread (beam size) of the beam after energy conversion will increase due to scattering between the beam and the range shifter.

[0015] In recent years, in particle beam therapy, a scanning irradiation method in which the affected area is three-dimensionally scanned with a narrow-diameter beam has become widespread, and it is desirable to suppress the expansion of the beam size as much as possible in order to form a high-precision dose distribution by the scanning irradiation method.

[0016] Therefore, when using the energy conversion device described in Patent Document 2, the spread of the energy of the beam particles (hereinafter referred to as momentum dispersion) increases when the beam passes through the range shifter, and there is a risk that the passing efficiency of the high-energy beam transport system will decrease and the effective beam current will decrease. Therefore, it is difficult to apply the technology as it is, and improvement is required.

[0017] The present invention has been made in view of the above problems, and an object thereof is to provide a circular accelerator and a particle beam therapy system that can irradiate a high-current and high-quality beam and are still low-cost.

Means for Solving the Problems

[0018] The present invention includes a plurality of means for solving the above problems. For example, a circular accelerator that accelerates a beam of charged particles orbiting in a magnetic field so that the closed orbits for each energy of the beam are eccentric, a beam extraction port that extracts beams of different energies from the closed orbit, a first deflection electromagnet and a second deflection electromagnet that deflect the beam extracted from the beam extraction port, and a control unit that controls the excitation amounts of the first deflection electromagnet and the second deflection electromagnet according to the energy of the extracted beam. The control unit is characterized in that when the energy of the extracted beam is the maximum energy in the design of the circular accelerator, both the first deflection electromagnet and the second deflection electromagnet are excited to deflect the beam.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a circular accelerator and a particle beam therapy system that can irradiate a high-current and high-quality beam and are also low-cost. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0021] Embodiments of the circular accelerator and particle beam therapy system of the present invention will be described below with reference to the drawings. In the drawings used in this specification, the same or corresponding components are denoted by the same or similar reference numerals, and repeated descriptions of these components may be omitted.

[0022] <Embodiment 1> Embodiment 1 of the circular accelerator and particle beam therapy system of the present invention will be described with reference to FIGS. 1 and 2.

[0023] First, the overall configuration of the particle beam therapy system including the circular accelerator will be described with reference to FIG. 1. FIG. 1 is a schematic diagram showing the configuration of the particle beam therapy system using the circular accelerator according to Embodiment 1.

[0024] The particle beam therapy system 100 according to the present embodiment shown in FIG. 1 includes a circular accelerator 1 that accelerates and extracts a beam of charged particles orbiting in a magnetic field, a high-energy beam transport system 30 that transports the charged particle beam accelerated by the circular accelerator 1, an irradiation nozzle 53 that irradiates the charged particle beam transported by the high-energy beam transport system 30, a control device 40, and the like.

[0025] In the particle beam therapy system 100, the beam extracted from the circular accelerator 1 is transported by the high-energy beam transport system 30 and irradiated to the affected part 52 of the patient 51 to treat lesions such as cancer.

[0026] The downstream stage of the high-energy beam transport system 30 is a rotating gantry 50. The rotating gantry 50 can irradiate the beam from a plurality of different directions by rotating around the patient 51.

[0027] An irradiation nozzle 53 that shapes the beam from the circular accelerator 1 according to the shape of the affected part 52 is provided at the straight part at the most downstream of the rotating gantry 50.

[0028] Devices such as electromagnets constituting the high-energy beam transport system 30 and the rotating gantry 50 are connected to the control device 40 in the same manner as the circular accelerator 1.

[0029] In particle beam therapy, the distance that the beam travels through the body of the patient 51 (hereinafter referred to as the range) is controlled by the energy of the beam irradiated to the patient 51.

[0030] The control device 40 controls the circular accelerator 1 based on the information on the irradiation position and irradiation dose of the beam (hereinafter referred to as the treatment plan) created in advance for each patient 51, and adjusts the energy of the beam extracted from the circular accelerator 1 to a value corresponding to the depth of the affected part 52. The control device 40 controls the first deflection electromagnet 21, the second deflection electromagnet 22, the high-energy beam transport system 30, and the rotating gantry 50 based on the treatment plan, and the beam extracted from the circular accelerator 1 is irradiated to the affected part 52.

[0031] Next, the configuration of the circular accelerator will be described with reference to FIG. 2. FIG. 2 shows an overview of the circular accelerator 1 of the present embodiment, particularly a schematic diagram of a beam orbit adjustment device provided outside the main body 10 of the circular accelerator 1.

[0032] As shown in FIG. 2, the circular accelerator 1 includes magnetic poles 11, coils 12, an extraction magnetic field generation device 13, and a yoke 14, and a beam extraction port 15 is formed in the yoke 14. When a predetermined current is passed through the coil 12, a magnetic field (hereinafter referred to as the main magnetic field) for circulating the beam in the circular accelerator 1 is generated between the magnetic poles 11, and a circular circulating beam orbit 16 is formed on the orbit plane. The radius of the circulating beam orbit 16 increases as the kinetic energy of the beam particles (hereinafter simply referred to as energy) increases.

[0033] In the circular accelerator 1 of the present embodiment, the closed orbits for each beam energy are eccentric. More specifically, the center of the circulating beam orbit 16 moves away from the extraction magnetic field generation device 13 as the energy increases, and an orbit concentration region 17 where the circulating beam orbits 16 with different energies gather in a narrow region is formed in the vicinity of the extraction magnetic field generation device 13. By forming the orbit concentration region 17, the circular accelerator 1 can extract beams with different energies from the common extraction port 15 without changing the intensity of the main magnetic field.

[0034] The extraction magnetic field generator 13 deflects the beam incident on the extraction magnetic field generator 13 and guides the beam to the extraction port 15. The extraction magnetic field generator 13 is composed of, for example, a septum coil formed along the beam orbit. The septum coil can adjust the direction and amount of beam deflection according to the energy by changing the current flowing through the coil. In this embodiment, an example in which the extraction magnetic field generator 13 is composed of a septum coil has been described. However, instead of the septum coil, a magnetic field correction structural member (hereinafter referred to as a magnetic channel) made of a magnetic material such as iron may be arranged along the beam orbit. The magnetic channel does not require a power source for excitation. On the other hand, the generated magnetic field is constant regardless of the energy of the beam. Note that the extraction magnetic field generator 13 may be configured by arranging both the septum coil and the magnetic channel.

[0035] Downstream of the extraction port 15 of the circular accelerator 1, a first deflection electromagnet 21 and a second deflection electromagnet 22 are installed. The orbit control device 18 of this embodiment includes a first deflection electromagnet 21, a second deflection electromagnet 22, power supplies 23, 24, and a control unit 40a (preferably a part of the control device 40). The first deflection electromagnet 21 is connected to the power supply 23, and the second deflection electromagnet 22 is connected to the power supply 24. By controlling the power supply 23 by the control unit 40a, the excitation current for exciting the first deflection electromagnet 21 is controlled. Also, by controlling the power supply 24 by the control unit 40a, the excitation current for exciting the second deflection electromagnet 22 is controlled.

[0036] The first deflection electromagnet 21 deflects the beam in a direction away from the center of the magnetic pole 11, that is, in the outer peripheral direction of the circular accelerator 1, and the second deflection electromagnet 22 deflects the beam in a direction approaching the center of the magnetic pole 11, that is, in the inner peripheral direction of the circular accelerator 1.

[0037] In this embodiment, as shown in FIG. 1, the diameter of the first deflection electromagnet 21 is larger than the diameter of the second deflection electromagnet 22 and the diameters of the deflection electromagnets 50a, 50b, 50c constituting the high energy beam transport system 30.

[0038] Further, as shown in FIG. 1, the second deflection electromagnet 22 has a diameter smaller than that of the first deflection electromagnet 21 but larger than the diameters of the deflection electromagnets 50a, 50b, and 50c that constitute the high-energy beam transport system 30. Note that the diameter of the second deflection electromagnet 22 does not necessarily have to be smaller than that of the first deflection electromagnet 21 and larger than the diameters of the deflection electromagnets 50a, 50b, and 50c, and it may be the same as the diameter of the first deflection electromagnet 21 or the same as the diameters of the deflection electromagnets 50a, 50b, and 50c. When the diameter of the second deflection electromagnet 22 is the same as that of the first deflection electromagnet 21 or the deflection electromagnets 50a, 50b, and 50c, since their specifications are shared, it is not necessary to manufacture the second deflection electromagnet as a deflection electromagnet with a dedicated specification, and cost reduction can be achieved.

[0039] Also, the diameter of the vacuum duct (omitted for illustration purposes) disposed inside the deflection electromagnet tends to be the same as the diameter of the deflection electromagnet. For example, the diameter of the vacuum duct in the portion where the first deflection electromagnet 21 is installed is larger than the diameter of the vacuum duct in the portion where the second deflection electromagnet 22 is installed and the diameters of the vacuum ducts in the portions where the deflection electromagnets 50a, 50b, and 50c are installed.

[0040] A high-energy beam transport system 30 for transporting the beam to the irradiation target is formed on the downstream side of the second deflection electromagnet 22, and profile monitors 31 and 32 for measuring the position and shape of the beam in a plane perpendicular to the beam traveling direction are installed in the straight portion immediately after the second deflection electromagnet 22 in the high-energy beam transport system 30. Note that the installation location of the profile monitor for measuring the position and shape of this beam is not limited to within the high-energy beam transport system 30, and it can be provided at other locations, for example, within the orbit control device 18.

[0041] The first deflection electromagnet 21 is connected to the power supply 23, and the second deflection electromagnet 22 is connected to the power supply 24. The power supply 23, the power supply 24, the circular accelerator 1, and the profile monitor 31 are connected to the control device 40.

[0042] A method for providing an accelerator system that can irradiate a high-current and high-quality beam with the circular accelerator 1 of the present embodiment and is still low-cost will be described.

[0043] The circular accelerator 1 of the present embodiment can extract beams with different energies from a common extraction port 15 without changing the intensity of the main magnetic field. However, the beam trajectory at the extraction port 15 may differ for each energy within the range that can pass through the extraction port 15.

[0044] The cause of the beam trajectory deviation at this extraction port 15 is, for example, that the septum coil constituting the extraction magnetic field generator 13 cannot generate a magnetic field with sufficient intensity, or that the magnetic field generated by the magnetic channel is constant regardless of the energy. The degree of deficiency in the magnetic field intensity of the septum coil depends on the design of the circular accelerator 1, but when generating a main magnetic field with a high intensity (for example, about 2.5 T) for the purpose of miniaturizing the circular accelerator 1, the deficiency in the magnetic field intensity of the septum coil becomes a problem.

[0045] Also, when the extraction magnetic field generator 13 is constituted by a magnetic channel, the beam trajectory at the extraction port 15 changes according to the energy regardless of the design of the circular accelerator 1.

[0046] When connecting a high-energy beam transport system immediately after the extraction port 15, the constituent devices of the high-energy beam transport system 30, such as electromagnets such as deflection electromagnets 50a, 50b, 50c and quadrupole electromagnets, and measuring devices such as profile monitors 31, 32 need to be designed large so that beams of all energies can pass through the inside. As a result, in an accelerator system using a conventional circular accelerator, there is a risk of increasing the installation area and manufacturing cost of the high-energy beam transport system.

[0047] Therefore, in the circular accelerator 1 of the present embodiment, the first deflection electromagnet 21 and the second deflection electromagnet 22 are installed on the downstream side of the extraction port 15, and the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 are controlled so that the orbits of beams with different energies coincide on the downstream side of the second deflection electromagnet 22. Thereby, in the circular accelerator 1 of the present embodiment, it is possible to prevent the expansion of the beam passage region in the high-energy beam transport system 30 and to reduce the size of the devices constituting the high-energy beam transport system 30.

[0048] Note that the excitation amount of the electromagnet represents the intensity of the magnetic field generated by the electromagnet, and generally is proportional to the current flowing through the coil constituting the electromagnet. The current flowing through the coil of the first deflection electromagnet 21 is controlled by the power supply 23, and the current flowing through the coil of the second deflection electromagnet 22 is controlled by the power supply 24.

[0049] Next, a method for making the orbits of beams with different energies coincide in the high-energy beam transport system 30 using the first deflection electromagnet 21 and the second deflection electromagnet 22 will be described.

[0050] Since a magnetic field is generated inside the circular accelerator 1 to deflect the beam toward the inner peripheral side of the circular accelerator 1, at the extraction port 15, the orbit of the beam with higher energy is located more on the outer peripheral side, and the orbits are different for each energy.

[0051] In FIG. 2, the orbit 25 represents the design beam orbit (hereinafter, design orbit) at the maximum energy (hereinafter, highest energy) extracted from the circular accelerator 1, and the orbit 26 represents an example of the beam orbit at an energy lower than the highest energy. Since the orbits of the beams extracted from the circular accelerator 1 are different for each energy, the intensity of the deflection magnetic field generated by the first deflection electromagnet 21 and the second deflection electromagnet 22 needs to be controlled according to the energy of the beam extracted from the circular accelerator 1, and the amount by which the first deflection electromagnet 21 and the second deflection electromagnet 22 deflect the beam needs to be different for each energy of the beam.

[0052] Furthermore, in the control unit 40a of the control device 40, when the energy of the extracted beam is the maximum energy in the design of the circular accelerator 1, both the first deflection electromagnet 21 and the second deflection electromagnet 22 are excited to deflect the beam. At this time, preferably, when the energy of the extracted beam is the minimum energy in the design of the circular accelerator 1, it is desirable that both the first deflection electromagnet 21 and the second deflection electromagnet 22 are excited to deflect the beam.

[0053] Here, the first deflection electromagnet 21 deflects the beam in the outer peripheral direction, the second deflection electromagnet 22 deflects the beam in the inner peripheral direction, and the magnetic field strengths generated by the first deflection electromagnet 21 and the second deflection electromagnet 22 are controlled so that the beam orbit 26 of each energy at the exit of the second deflection electromagnet 22 coincides with the design orbit 25 when the energy of the beam is the maximum value in the design.

[0054] The design value of the excitation amount of the first deflection electromagnet 21 and the design value of the excitation amount of the second deflection electromagnet 22 at the maximum energy are not both 0, and the design orbit 25 at the maximum energy is bent by the first deflection electromagnet 21 and the second deflection electromagnet 22. In the circular accelerator 1 of the present embodiment, the beam orbits in the high-energy beam transport system 30 are made to coincide with the design orbit 25 at the maximum energy by bending the orbit 26 of the beam with an energy lower than the maximum energy more than the design orbit 25 at the maximum energy.

[0055] The excitation amount of the first deflection electromagnet 21 and the excitation amount of the second deflection electromagnet 22 are determined in an adjustment operation (hereinafter, beam adjustment) performed before the circular accelerator 1 is used for beam irradiation such as particle beam therapy.

[0056] When adjusting the beam orbit 26 at an energy lower than the maximum energy, the control device 40 controls the circular accelerator 1 so that the energy of the beam extracted from the circular accelerator 1 becomes the target value.

[0057] In addition, the control device 40 controls the power supplies 23 and 24, and sets the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 to the design values in the energy to be adjusted. The design values of the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 are derived in advance by analyzing the beam orbit using a computer or the like.

[0058] The position and inclination of the beam in the high-energy beam transport system 30 are measured using the profile monitors 31 and 32. Since the magnetic field generated by the circular accelerator 1 has a deviation from the design value due to manufacturing errors of the magnetic poles 11 or the like, the position and inclination of the beam in the high-energy beam transport system 30 may not completely match the design value in the initial state.

[0059] Therefore, in the circular accelerator 1 of the present embodiment, the profile monitors 31 and 32 are used to measure the beam position and the inclination of the beam to measure the deviation from the design value, and the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 are adjusted so that the beam position and the inclination match the design values.

[0060] Note that the deviation of the beam orbit at the extraction port 15 to the inner peripheral side or the outer peripheral side can be obtained by measuring with the profile monitors 31 and 32 in the high-energy beam transport system 30. Specifically, by obtaining the position and inclination of the beam in the high-energy beam transport system 30, it is possible to determine whether the beam orbit at the extraction port 15 is deviated to the inner peripheral side or the outer peripheral side from the design orbit 25.

[0061] Since the change amount of the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 and the change amounts of the position and inclination of the beam in the high-energy beam transport system 30 are in a linear relationship, the adjustment amount of the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 can be easily obtained from the measurement results of the beam position and inclination. The control device 40 may derive the change amount of the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 based on the measurement results of the beam position and inclination, or the adjuster of the circular accelerator 1 may separately calculate from the measurement results of the beam position and inclination and input it to the control device 40.

[0062] After adjusting the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22, the position and inclination of the beam in the high-energy beam transport system 30 are measured again to confirm that the beam orbit coincides with the design orbit 25 at the maximum energy. If there is an unacceptable deviation between the beam orbit and the design orbit 25 at the maximum energy at this stage, the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 are adjusted again in the same procedure. The adjustment results of the excitation amounts are stored in the control device 40, and when actually performing beam irradiation by the circular accelerator 1, the first deflection electromagnet 21 and the second deflection electromagnet 22 are excited based on this adjustment result.

[0063] Next, a method for adjusting the beam orbit at the maximum energy in the circular accelerator 1 of the present embodiment will be described.

[0064] In the present embodiment, the beam orbits 26 at each energy in the high-energy beam transport system 30 are adjusted to coincide with the design orbit 25 at the maximum energy. However, since it is expected that the beam orbit itself at the maximum energy will deviate from the design orbit 25 due to the influence of magnetic field errors, etc., it is necessary to adjust the beam orbit for the maximum energy as well as for the other energies.

[0065] When the beam orbit at the maximum energy at the extraction port 15 is located on the inner peripheral side of the design orbit 25, the beam orbit can be deflected to the outer peripheral side by setting the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 to values higher than the design values, and the beam orbit at the maximum energy can be made to coincide with the design orbit 25.

[0066] Conversely, when the beam orbit at the maximum energy at the extraction port 15 is located on the outer peripheral side of the design orbit 25, the beam orbit at the maximum energy can be made to coincide with the design orbit 25 by setting the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 to values lower than the design values.

[0067] Next, the effects of the present embodiment will be described.

[0068] In the circular accelerator 1 in the particle beam therapy system 100 according to the first embodiment of the present invention described above, the circular accelerator accelerates a beam of charged particles orbiting in a magnetic field such that the closed orbit for each beam energy is eccentric, and has a beam extraction port for extracting beams of different energies from the closed orbit, a first deflection electromagnet 21 and a second deflection electromagnet 22 for deflecting the beam extracted from the beam extraction port, and a control unit 40a for controlling the excitation amounts of the first deflection electromagnet and the second deflection electromagnet according to the energy of the extracted beam. When the energy of the extracted beam is the maximum energy in the design of the circular accelerator 1, the control unit 40a excites both the first deflection electromagnet 21 and the second deflection electromagnet 22 to deflect the beam. Further, the diameter of the first deflection electromagnet 21 may be configured to be larger than the diameters of the deflection electromagnets 50a, 50b, 50c constituting the high energy beam transport system 30.

[0069] Thus, in the circular accelerator 1 of the present embodiment, since the design values of the excitation amounts of the first deflection electromagnet 21 and the second deflection electromagnet 22 are set to non-zero values with respect to the design orbit 25 at the maximum energy, even when the beam orbit of the maximum energy at the extraction port 15 is on the outer peripheral side of the design orbit 25, it is possible to make the beam orbit of the maximum energy coincide with the design orbit 25. Thereby, in the circular accelerator 1 of the present embodiment, the beam orbit in the high energy beam transport system 30 can be efficiently corrected, the expansion of the devices constituting the high energy beam transport system 30 can be prevented, and the manufacturing cost of the accelerator system can be suppressed.

[0070] In addition, since the closed orbits of beams with different energies in the circular accelerator 1 of the present embodiment are arranged eccentrically, it is possible to extract beams with different energies from the common extraction port 15. As a result, when changing the energy of the irradiation beam, the circular accelerator 1 does not need to install an energy absorber in the high-energy beam transport system. Therefore, an increase in the irradiation beam size due to scattering with the energy absorber can be prevented, and a high-quality beam can be irradiated. Furthermore, in the circular accelerator 1, since it is not necessary to change the intensity of the main magnetic field of the circular accelerator 1 in order to change the energy of the extracted beam, it is possible to continuously extract the beam from the circular accelerator 1, and a high beam current can be obtained. In particular, in the scanning irradiation method of suppressing the expansion of the size of the beam irradiated to the patient 51 and three-dimensionally scanning the affected part 52 with the beam, highly accurate irradiation can be performed. Moreover, since the circular accelerator 1 of the present embodiment can irradiate a high-current beam regardless of the beam energy, in particle beam therapy, the treatment can be completed in a shorter time than in the conventional case, and the burden on the patient can be further reduced.

[0071] In the circular accelerator 1 of the present embodiment, the design orbit 25 of the highest energy is bent by the first deflection electromagnet 21 and the second deflection electromagnet 22, that is, the design value of the excitation amount of these deflection electromagnets corresponding to the highest energy is a non-zero value. Due to this feature, even when the beam orbit before beam adjustment at the highest energy in the circular accelerator 1 is located on the outer peripheral side of the design orbit 25, the beam orbit at the highest energy can be corrected, and an increase in the beam passing region in the high-energy beam transport system 30 can be suppressed.

[0072] According to the particle beam therapy system 100 of the present embodiment, it is possible to irradiate a high-current and high-quality beam and to provide a low-cost accelerator system.

[0073] In addition, since the diameter of the second deflection electromagnet 22 is smaller than the diameter of the first deflection electromagnet 21, the manufacturing cost can be reduced.

[0074] Furthermore, the intensity of the magnetic fields generated by the first deflection electromagnet 21 and the second deflection electromagnet 22 is controlled so that the beam orbit 26 of each energy at the exit of the second deflection electromagnet 22 coincides with the design orbit 25 when the energy of the beam is the maximum value in design, thereby reducing the passing area of the beam in the high-energy beam transport system and making it possible to reduce the cost of the accelerator system.

[0075] The circular accelerator 1 of this embodiment accelerates a beam of charged particles orbiting in a magnetic field so that the closed orbit for each beam energy is eccentric, extracts the accelerated beam from the closed orbit, and guides it to the extraction port 15. The beam orbit after being extracted from the extraction port 15 becomes a different orbit according to the energy of the beam. However, as in this embodiment, a plurality of deflection electromagnets are installed at a position downstream of the extraction port 15 of the circular accelerator 1 and upstream of the high-energy beam transport system 30, and by controlling the excitation amount of these deflection electromagnets according to the energy of the beam, the beam orbits can be made to substantially coincide within the high-energy beam transport system 30. Therefore, the particle beam therapy system can be miniaturized. In particular, when the extraction magnetic field generator 13 is configured by a magnetic channel, since the magnetic field generated by the magnetic channel is constant, the beam orbit after being extracted from the extraction port 15 becomes a greatly different orbit according to the energy of the beam, and the effect of further miniaturizing the particle beam therapy system can be obtained.

[0076] In addition, in the present Embodiment 1 and Embodiments 2 and 3 described later, the case where there are two deflection electromagnets (the first deflection electromagnet and the second deflection electromagnet) constituting the orbit control devices 18, 18A, and 18B is described. However, the number of deflection electromagnets installed in the orbit control device provided between the exit side of the main body of the circular accelerator and the high-energy beam transport system may be two or more and is not particularly limited.

[0077] <Embodiment 2> The circular accelerator and the particle beam therapy system according to Embodiment 2 of the present invention will be described with reference to FIG. 3. FIG. 3 shows a schematic diagram of the circular accelerator 1A of this embodiment.

[0078] The circular accelerator 1A of the present embodiment shown in FIG. 3 basically has the same configuration as the circular accelerator 1 described in the first embodiment. However, the orbit control device 18A of the embodiment includes a first deflection electromagnet 61, a second deflection electromagnet 62, power supplies 63 and 64, and a control unit 40a1 (preferably a part of the control device 40A), and is different from the first embodiment in that the first deflection electromagnet 61 and the second deflection electromagnet 62 deflect the beam in both the outer circumferential direction and the inner circumferential direction of the circular accelerator 1A.

[0079] The power supply 63 for exciting the first deflection electromagnet 61 and the power supply 64 for exciting the second deflection electromagnet 62 are bipolar power supplies capable of switching the direction of the current flowing through the coil constituting the first deflection electromagnet 61 or the second deflection electromagnet 62 in order to deflect the beam in both directions.

[0080] Next, a method for matching the orbits of beams with different energies using the first deflection electromagnet 61 and the second deflection electromagnet 62 in the high-energy beam transport system 30 will be described.

[0081] In the present embodiment, the intensities of the magnetic fields generated by the first deflection electromagnet 61 and the second deflection electromagnet 62 are controlled so that the beam orbits of each energy at the exit of the second deflection electromagnet 62 coincide with the design orbit 65 when the energy of the beam is greater than the minimum value in design and less than the maximum value in design.

[0082] For example, a reference energy (reference energy) is defined between the minimum energy (hereinafter, minimum energy) and the maximum energy taken out from the circular accelerator 1A, and the excitation amounts of the first deflection electromagnet 61 and the second deflection electromagnet 62 are controlled so that the beam orbits of each energy in the high-energy beam transport system 30 coincide with the design orbit 65 at the reference energy.

[0083] At this time, the first deflection electromagnet 61 deflects the beam with the lowest energy (orbit 66) in the outer peripheral direction and deflects the beam with the highest energy (orbit 67) in the inner peripheral direction. The second deflection electromagnet 62 deflects the beam with the lowest energy in the inner peripheral direction and deflects the beam with the highest energy in the outer peripheral direction.

[0084] In beam adjustment, the procedure for adjusting the excitation amounts of the first deflection electromagnet 61 and the second deflection electromagnet 62 using the profile monitors 31 and 32 in the high-energy beam transport system 30 is the same as that in the first embodiment.

[0085] The other configurations and operations are substantially the same as those of the circular accelerator 1 and the particle beam therapy system of the first embodiment described above, and the details are omitted.

[0086] In the circular accelerator 1A and the particle beam therapy system according to the second embodiment of the present invention, since the directions in which the first deflection electromagnet 61 and the second deflection electromagnet 62 deflect the beam are different between the lowest energy and the highest energy, the beam orbit in the high-energy beam transport system 30 can be efficiently corrected in the same manner as in the first embodiment. For example, when the beam orbit 67 before adjustment at the highest energy is on the outer peripheral side of the designed orbit 65 at the highest energy, the beam orbit 67 can be made to coincide with the designed orbit 65 by weakening the excitation amounts of the first deflection electromagnet 61 and the second deflection electromagnet 62 from the designed values.

[0087] Further, the power supply 63 for exciting the first deflection electromagnet 61 and the power supply 64 for exciting the second deflection electromagnet 62 are configured by bipolar power supplies capable of switching the direction of the current flowing through the coils constituting the first deflection electromagnet 61 or the second deflection electromagnet 62, so that the magnetic field strength of the deflection electromagnet can be further reduced.

[0088] Furthermore, the intensity of the magnetic fields generated by the first deflection electromagnet 61 and the second deflection electromagnet 62 is controlled such that the beam trajectory of each energy at the exit of the second deflection electromagnet 62 coincides with the design trajectory 65 when the energy of the beam is greater than the minimum value in design and less than the maximum value in design. In the circular accelerator 1A of the present embodiment, the beam trajectory 66 with the lowest energy only needs to be deflected to the position of the design trajectory 65 at the reference energy, and compared with Embodiment 1 where the beam needs to be deflected to the position of the design trajectory 65 at the highest energy, the maximum value of the excitation amount of the first deflection electromagnet 61 and the second deflection electromagnet 62 can be reduced. Conversely, even when the maximum value of the excitation amount of these deflection electromagnets becomes equal to the value in Embodiment 1, in the present embodiment, the length in the traveling direction of the first deflection electromagnet 61 and the second deflection electromagnet 62 (hereinafter, the magnetic pole length) is shortened, and the accelerator system can be miniaturized.

[0089] <Embodiment 3> The circular accelerator and the particle beam therapy system according to Embodiment 3 of the present invention will be described with reference to FIG. 4. FIG. 4 is a schematic diagram of the circular accelerator 1B of the present embodiment.

[0090] The circular accelerator 1B of the present embodiment shown in FIG. 4 basically has the same configuration as the circular accelerator 1 described in Embodiment 1. However, the orbit control device 18B of the embodiment includes a first deflection electromagnet 21, a second deflection electromagnet 22B, a quadrupole electromagnet 71, power supplies 23, 24, 72, and a control unit 40a2 (preferably a part of the control device 40B), and is different from Embodiment 1 in that the quadrupole electromagnet 71 is installed downstream of the first deflection electromagnet 21 and upstream of the second deflection electromagnet 22B.

[0091] The quadrupole electromagnet 71 is connected to the power supply 72, and the power supply 72 is connected to the control device 40B. Similar to the first deflection electromagnet 21 and the second deflection electromagnet 22B, the excitation amount of the quadrupole electromagnet 71 is controlled by the control device 40B via the power supply 72.

[0092] In the circular accelerator 1B of the present embodiment, the orbit control device 18B includes the quadrupole electromagnet 71 and is configured to converge the passing beam in the horizontal and vertical directions. The beam extracted from the circular accelerator 1B gradually expands in the horizontal and vertical directions. However, by installing the quadrupole electromagnet 71 as in the present embodiment, the expansion of the beam size downstream of the quadrupole electromagnet 71 can be suppressed. Thereby, it is possible to prevent beam loss caused by the beam colliding with structures such as the second deflection electromagnet 22B and the vacuum duct. Further, since the circular accelerator 1B of the present embodiment is configured to include the quadrupole electromagnet 71 on the downstream side of the first deflection electromagnet 21 and on the upstream side of the second deflection electromagnet 22B, the beam passing through the first deflection electromagnet 21 can be converged in the horizontal or vertical direction using the quadrupole electromagnet 71, the expansion of the beam size in the second deflection electromagnet 22B is suppressed, the second deflection electromagnet 22B can be further miniaturized, and the manufacturing cost of the second deflection electromagnet 22B can be reduced.

[0093] Also, in the circular accelerator 1B of the present embodiment, the excitation amount of the quadrupole electromagnet 71, that is, the intensity of the generated magnetic field, is adjusted according to the energy of the beam.

[0094] Other configurations and operations are substantially the same as those of the circular accelerator 1 and the particle beam therapy system of the aforementioned embodiment 1, and the details are omitted.

[0095] In the circular accelerator 1B and the particle beam therapy system of Embodiment 3 of the present invention, substantially the same effects as those of the circular accelerator 1 and the particle beam therapy system of Embodiment 1 described above can be obtained.

[0096] In the circular accelerator 1B of the present embodiment, by providing the quadrupole electromagnet 71 on the upstream side of the second deflection electromagnet 22B, the energy dependence of the beam size in the high-energy beam transport system 30 can be reduced, and the beam adjustment after the high-energy beam transport system 30 can be simplified.

[0097] In the circular accelerator 1B of the present embodiment, since the quadrupole electromagnet 71 is installed on the downstream side of the first deflection electromagnet 21, the beam emerging from the main body 10 of the circular accelerator 1B is quickly kicked by the first deflection electromagnet 21 to deflect the beam orbit, and it is possible to suppress the increase in the diameter of the second deflection electromagnet 22B.

[0098] In the circular accelerator 1B of the present embodiment, the intensity of the magnetic field generated by the quadrupole electromagnet 71 is set to different values for each beam energy, so that the effect of suppressing the expansion of the beam size can be obtained more reliably.

[0099] In the circular accelerator 1B of the present embodiment, the configuration in which one quadrupole electromagnet is installed between the first deflection electromagnet 21 and the second deflection electromagnet 22B has been described as an example. However, two or more quadrupole electromagnets may be installed in this region. When a plurality of quadrupole electromagnets are installed between the first deflection electromagnet 21 and the second deflection electromagnet 22B, it is possible to further suppress the beam size at the exit of the second deflection electromagnet 22B to be smaller than when only one quadrupole electromagnet is installed.

[0100] Also, in the present embodiment, the example in which the quadrupole electromagnet 71 is installed on the downstream side of the first deflection electromagnet 21 has been described. However, the location where the quadrupole electromagnet 71 is installed is not limited to this, and one or more may be installed on the upstream side of the first deflection electromagnet 21.

[0101] Furthermore, the quadrupole electromagnet 71 of the present embodiment is also applicable to Embodiment 2. That is, the orbit control device of Embodiment 2 may be configured to include one or more quadrupole electromagnets on the upstream side of the second deflection electromagnet 62. Furthermore, preferably, one or more quadrupole electromagnets may be installed on the downstream side of the first deflection electromagnet 61 of Embodiment 2.

[0102] <Others> Note that the present invention is not limited to the above-described embodiments, and various modifications are included. The above embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.

[0103] Also, it is possible to replace a part of the configuration of a certain embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of a certain embodiment. Also, it is possible to add, delete, or replace other configurations for a part of the configuration of each embodiment.

Description of Reference Numerals

[0104] 1, 1A, 1B... circular accelerators 10... main body 11... magnetic poles 12... coils 13... extraction magnetic field generator 14... yoke 15... extraction port 16... circulating beam orbit 17... orbit focusing region 18, 18A, 18B... orbit control devices 21, 61... first deflection electromagnets 22, 62, 22B... second deflection electromagnets 23, 24, 63, 64... power supplies 25, 65... designed orbit 26, 66, 67... beam orbit 30... high-energy beam transport system 31, 32... profile monitors 40, 40A, 40B... control devices 40a, 40a1, 40a2... control units 50... rotating gantry 50a, 50b, 50c... deflection electromagnets 51... patient 52... affected part 53... irradiation nozzle 71... quadrupole electromagnets 72... power supply 100... particle beam therapy system

Claims

1. A circular accelerator that accelerates a beam of charged particles orbiting in a magnetic field so that a closed orbit for each energy of the beam becomes eccentric, a beam outlet for extracting beams of different energies from the closed orbit; a first deflection electromagnet and a second deflection electromagnet for deflecting the beam extracted from the beam outlet; a control unit that controls an excitation amount of the first bending electromagnet and the second bending electromagnet in accordance with energy of the extracted beam, The control unit is When the energy of the extracted beam is the maximum energy in the design of the circular accelerator, both of the first bending electromagnet and the second bending electromagnet are excited to deflect the beam. A circular accelerator characterized by:

2. 2. The circular accelerator according to claim 1, The control unit is When the energy of the extracted beam is a minimum energy in the design of the circular accelerator, both of the first bending electromagnet and the second bending electromagnet are excited to deflect the beam. A circular accelerator characterized by:

3. 2. The circular accelerator according to claim 1, The strength of the magnetic field generated by the first bending electromagnet and the second bending electromagnet is controlled so that the beam trajectory of each energy at the outlet of the second bending electromagnet coincides with a design trajectory when the energy of the beam is at a design maximum value. A circular accelerator characterized by:

4. 2. The circular accelerator according to claim 1, A first power supply for exciting the first deflection electromagnet and a second power supply for exciting the second deflection electromagnet are configured by a bipolar power supply capable of switching the direction of the current flowing through the coil constituting the first deflection electromagnet or the second deflection electromagnet. A circular accelerator characterized by:

5. 5. The circular accelerator according to claim 4, The strength of the magnetic field generated by the first bending electromagnet and the second bending electromagnet is controlled so that the beam trajectory of each energy at the outlet of the second bending electromagnet coincides with a design trajectory when the energy of the beam is greater than a design minimum value and less than a design maximum value. A circular accelerator characterized by:

6. 2. The circular accelerator according to claim 1, The second deflection electromagnet is disposed upstream of the second deflection electromagnet and further includes one or more quadrupole electromagnets. A circular accelerator characterized by:

7. 7. The circular accelerator according to claim 6, The quadrupole electromagnet is disposed downstream of the first bending electromagnet. A circular accelerator characterized by:

8. 7. The circular accelerator according to claim 6, The strength of the magnetic field generated by the quadrupole electromagnet is set to a different value for each energy of the beam. A circular accelerator characterized by:

9. A particle beam therapy system comprising the circular accelerator according to any one of claims 1 to 8.

10. A circular accelerator according to any one of claims 1 to 8; a beam transport system that transports the beam extracted from the circular accelerator; an irradiation device that irradiates the beam transported by the beam transport system, the beam transport system includes a beam detector that measures a position and an inclination of the beam passing through the beam transport system; The control unit controls the excitation amounts of the first bending electromagnet and the second bending electromagnet so that the beam trajectory calculated from the position and inclination of the beam becomes a designed beam trajectory. A particle beam therapy system comprising:

11. a circular accelerator that accelerates a beam of charged particles orbiting in a magnetic field so that a closed orbit for each energy of the beam becomes eccentric; a beam transport system for transporting the charged particle beam accelerated by the circular accelerator; an irradiation device that irradiates the charged particle beam transported by the beam transport system, The circular accelerator comprises: a first deflection electromagnet and a second deflection electromagnet disposed downstream of a beam outlet for extracting the beams of different energies from the closed orbit of the circular accelerator, the first deflection electromagnet and the second deflection electromagnet deflecting the beams extracted from the beam outlet; a control unit that controls an excitation amount of the first bending electromagnet and the second bending electromagnet in accordance with the energy of the extracted beam, The diameter of the first bending electromagnet is larger than the diameter of the bending electromagnet constituting the beam transport system. A particle beam therapy system comprising:

12. The particle beam therapy system according to claim 11, The diameter of the second bending electromagnet is smaller than the diameter of the first bending electromagnet. A particle beam therapy system comprising:

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