Accelerators and particle beam therapy equipment

Abstract

To provide an accelerator capable of improving the beam usage efficiency than before, and a piece of particle beam therapy equipment.SOLUTION: A circular accelerator 30 is a device for applying a static magnetic field that orbits the charged particle beam, a frequency-modulated high-frequency accelerating electric field that accelerates a charged particle beam, and a high-frequency disturbance electric field that emits a charged particle beam. After stopping the high-frequency accelerating electric field, the orbiting frequency of the charged particle beam or the kinetic energy of the charged particle beam orbiting inside the circular accelerator 30 is found, and a high-frequency disturbance electric field is generated according to the determined circulating frequency or kinetic energy.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an accelerator and a particle beam therapy device. [Background technology]

[0002] Patent Document 1 describes, as an example of a synchrocyclotron for extracting beams of various energies, that the synchrocyclotron includes a magnetic unit including a valley sector and a peak sector, is configured to create a z-component of the main magnetic field, and has a radial tune of a continuous orbit that is other than 1 and falls within 1±0.1 for all values ​​of the mean radius between a low radius and a high radius corresponding to the respective mean radial positions of charged particles at low and high energies.

[0003] Patent Document 2 describes that in a circular accelerator that accelerates a charged particle beam while increasing the orbital radius by applying high frequency waves in a main magnetic field, the charged particle beam is emitted by applying high frequency waves to the charged particle beam that have a different frequency from the high frequency waves used for acceleration.

[0004] Non-Patent Document 1 describes an example of a compact superconducting synchrocyclotron as part of a small footprint proton therapy system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Registration No. 11160159 [Patent Document 2] Japanese Patent Application Publication No. 2019-133745 [Non-patent literature]

[0006] [Non-Patent Document 1] W. Kleeven, “The IBA Superconducting Synchrocyclotron Project S2C2”, Proceedings of Cyclotrons 2013 Summary of the Invention [Problem to be solved by the invention]

[0007] Particle therapy, a cancer treatment method, irradiates the affected area with a beam of charged particles such as protons or carbon ions. The particle therapy equipment used in particle therapy adjusts the energy and spatial spread of the charged particle beam to form a dose distribution that matches the shape of the affected area. A particle therapy equipment includes an accelerator, a beam transport system, and an irradiation device.

[0008] An accelerator is a device that accelerates a charged particle beam to the energy required for treatment, and examples of accelerators used in particle beam therapy include synchrotrons, cyclotrons, and synchrocyclotrons.

[0009] The compactness of particle beam therapy equipment can be achieved by miniaturizing accelerators. The compactness of accelerators can be achieved by using superconducting magnets as electromagnets to deflect charged particle beams.

[0010] An example of an accelerator that uses superconducting electromagnets is the synchrocyclotron described in Non-Patent Document 1. In a synchrocyclotron, a particle beam orbits in a static magnetic field formed by a superconducting coil and is accelerated by a radio-frequency accelerating electric field synchronized with the orbit of the particle beam. In a synchrocyclotron, the orbital frequency of the beam decreases as it accelerates, so the frequency of the radio-frequency accelerating electric field is modulated to match the orbital frequency. The horizontal orbit of the beam in the synchrocyclotron is concentric for each energy, and a beam that has reached the maximum energy designed is extracted from the extraction channel. To use the extracted beam for treatment, it must be decelerated by a scatterer to an energy level appropriate for the depth of the affected area.

[0011] In contrast to this, circular accelerators described in Patent Documents 1 and 2 are accelerators in which the energy of the extracted beam can be varied.

[0012] In the circular accelerator described in Patent Document 1, a dynamic magnetic field that disturbs the beam is excited by a coil in a conventional synchrocyclotron, thereby emitting beams of various energies that circulate concentrically.

[0013] In the circular accelerator described in Patent Document 2, the main magnetic field distribution is formed so that the orbits of beams with different energies are offset radially from the center of the circular accelerator to one side, and the high-frequency electric field generated in the region where the beam orbits are concentrated increases the betatron oscillation amplitude, and a disturbance magnetic field is passed through the region to extract a beam of a specific energy.

[0014] Scanning irradiation is a method for forming the emitted beam into a dose distribution that matches the shape of the affected area. In this method, the dose distribution is formed by scanning the beam using a scanning magnet installed upstream of the affected area.

[0015] When increasing the betatron oscillation amplitude of a beam in a circular accelerator using a radio-frequency electric field, it is necessary to apply a radio-frequency electric field with a frequency determined by the beam's circulation frequency and the beam's betatron oscillation frequency.However, it has become clear that if there is a discrepancy in this frequency, the increase in the betatron oscillation amplitude will be suppressed, which may lead to a decrease in the final beam utilization efficiency, and it has become clear that improvement is desirable.

[0016] The present invention provides an accelerator and a particle beam therapy system that can improve beam utilization efficiency compared to conventional systems. [Means for solving the problem]

[0017] The present invention includes a plurality of means for solving the above-mentioned problems. One example of the present invention is a circular accelerator that applies a static magnetic field that circulates a charged particle beam, a frequency-modulated radio-frequency acceleration electric field that accelerates the charged particle beam, and a radio-frequency disturbance electric field that emits the charged particle beam, wherein the circular frequency or kinetic energy of the charged particle beam circulating inside the circular accelerator after the radio-frequency acceleration electric field is stopped is determined, and the radio-frequency disturbance electric field is generated in accordance with the determined circular frequency or kinetic energy. [Effects of the Invention]

[0018] According to the present invention, it is possible to improve the beam utilization efficiency compared to the prior art. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is an external view of a circular accelerator according to a first embodiment. [Figure 2] 1 is a cross-sectional view of a circular accelerator according to a first embodiment. [Figure 3] A view taken along the arrows A-A' in Figure 2. [Figure 4] A view taken along the arrows B-B' in Figure 2. [Figure 5] 3 is a control flowchart of the circular accelerator according to the first embodiment. [Figure 6] 3 is a control chart of the circular accelerator of the first embodiment. [Figure 7] Table data 1 of the circular accelerator of the first embodiment. [Figure 8] Table data 2 for the circular accelerator of Example 1. [Figure 9] Table data 3 for the circular accelerator of Example 1. [Figure 10] FIG. 10 is an external view of a circular accelerator according to a second embodiment. [Figure 11] FIG. 10 is a cross-sectional view of a circular accelerator according to a second embodiment. [Figure 12] 12 is a view taken along the line CC' in FIG. 11. [Figure 13] 10 is a control chart of the circular accelerator of the second embodiment. [Figure 14] Table data 1 of the circular accelerator of the second embodiment. [Figure 15] Table data 2 of the circular accelerator of the second embodiment. [Figure 16] 10 is a control flowchart of the circular accelerator according to the second embodiment. [Figure 17] FIG. 10 is a diagram showing the overall configuration of a particle beam therapy system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] The accelerator and particle beam therapy system of the present invention will be described below with reference to the accompanying drawings. In the drawings used in this specification, identical or corresponding components are designated by the same or similar reference numerals, and repeated explanations of these components may be omitted.

[0021] Example 1 A first embodiment of the accelerator of the present invention will be described with reference to FIGS. 1 to 9. FIG.

[0022] First, the overall configuration of the circular accelerator 30 will be described with reference to Fig. 1. Fig. 1 shows an external view of the circular accelerator 30.

[0023] The circular accelerator 30 of this embodiment shown in FIG. 1 applies a static magnetic field that circulates the charged particle beam, a frequency-modulated high-frequency acceleration electric field that accelerates the charged particle beam, and a high-frequency disturbance electric field that emits the charged particle beam. Its outer shell is formed by a main electromagnet 40 that can be separated in the vertical direction, and the beam acceleration region inside the main electromagnet 40 is kept in a vacuum.

[0024] An ion source 53 is installed above the main electromagnet 40 to generate a beam of ions to be injected into the main electromagnet 40. The beam generated by the ion source 53 passes through a low-energy beam transport line 51 and is injected from an ion injection section 55 provided near the center of the main magnetic pole 35 into a beam acceleration region inside the main electromagnet 40 where the beam is accelerated.

[0025] An ECR ion source, a laser ion source, or the like can be used as the ion source 53. When ions are injected from outside, they are injected into the beam acceleration region, for example, through an electrostatic inflector 56. The ion source 53 may be placed inside the evacuated beam acceleration region inside the main electromagnet 40, in which case a PIG-type ion source or the like is suitable.

[0026] FIG. 2 shows a cross-sectional view of the circular accelerator 30 taken along the central plane, and FIG. 3 shows a cross-sectional view of the circular accelerator 30 taken along the vertical direction (a view taken along the line AA' in FIG. 2).

[0027] The main electromagnet 40 is made up of a main magnetic pole 35, a yoke 37, and a main coil 38. The yoke 37 forms the exterior of the main electromagnet 40 and defines a roughly cylindrical region inside. The main coil 38 is an annular coil that is installed along the inner wall of the yoke 37. The main coil 38 is a superconducting coil, and is cooled by a cryostat 36 installed around the main coil 38.

[0028] Main magnetic poles 35 are installed vertically facing each other on the inner periphery of the main coil 38. The magnetic field formed by the energized main coils 38 and 42 and the main magnetic pole 35 is called the main magnetic field. The acceleration region is a region for accelerating the beam in the main magnetic field.

[0029] The yoke 37 has a number of through-holes. Among them, a beam through-hole 44 for emitting the accelerated beam, a coil through-hole 48 for drawing out various coil conductors inside the yoke 37, a vacuum through-hole 49, and a radio frequency system through-hole 50 for the radio frequency accelerating cavity 10 are provided on the connection surface of the yoke 37.

[0030] The RF accelerating cavity 10 is a resonant cavity and includes a dee electrode 12 , a dummy dee electrode 13 , an inner conductor 14 , and an outer conductor 15 .

[0031] The dee electrode 12 is a D-shaped hollow electrode connected to the inner conductor 14. The dummy dee electrode 13 is an electrode connected to the outer conductor 15 that surrounds the inner conductor 14 and is at ground potential. An acceleration gap 11 is formed between the dummy dee electrode 13 and the dee electrode 12. An acceleration voltage that is frequency-modulated by a radio-frequency acceleration voltage control device 20 is generated in the acceleration gap 11 between the dee electrode 12 and the dummy dee electrode 13. The acceleration gap 11 shown in Figure 2 is for the case where the number of harmonics is 1, i.e., the circular frequency and the acceleration frequency are the same. The shape of the acceleration gap 11 is formed according to the trajectory shape of the beam.

[0032] Here, the behavior of the beam from when it is injected into the circular accelerator 30 until it is extracted will be described.

[0033] The beam injected from the ion source 53 is accelerated by the radio frequency electric field and moves around in the main magnetic field while increasing in energy. As the beam accelerates, the radius of curvature of the orbit increases, forming a spiral orbit.

[0034] Here, within the beam acceleration region, the orbit that the beam passes through from the start of acceleration until it reaches maximum energy is called the circular orbit. Of the circular orbits, the orbit through which the beam with the lowest energy passes is called the minimum energy orbit 80, and the orbit through which the beam with the highest energy passes is called the maximum energy orbit 81, and the plane on which the circular orbit describes a spiral is called the orbital plane. When the orbital plane is considered as a two-dimensional polar coordinate system with the center of the acceleration region as the origin, the axis extending radially outward from the center is called the r-axis. The main magnetic field satisfies the beam stabilization condition, where the value n, expressed by the following equation (1), is greater than 0 and less than 1.

[0035]

number

[0036] In equation (1), ρ is the deflection radius of the design orbit, Bz is the magnetic field strength, and ∂Bz / ∂r is the magnetic field gradient in the r direction. At this time, a beam that deviates slightly radially from the design orbit is subjected to a restoring force that returns it to the design orbit, and at the same time, a beam that deviates perpendicular to the orbital plane is subjected to a restoring force from the main magnetic field in a direction that returns it to the orbital plane. This oscillation is called a betatron oscillation, and the frequency of this oscillation is called the betatron frequency.

[0037] The beam undergoes betatron oscillation near the designed orbit, and the ∂Bz / ∂r of the main magnetic field is designed to ensure stable orbit and acceleration of the beam. The frequency of oscillation per revolution is called the tune, and the beam's displacement on the r-axis outside the orbital plane per revolution is called the turn separation. The betatron oscillation of an orbiting beam in the orbital plane and perpendicular to the beam's orbit is called the horizontal betatron oscillation, and the tune is called the horizontal tune. The amplitude of betatron oscillation increases due to resonance when an appropriate radio-frequency voltage is applied. For a full-energy beam, the betatron frequency (horizontal tune) νr parallel to the orbital plane and perpendicular to the orbit is set to a value close to 1.

[0038] The main magnetic field distribution described above is formed by the main pole 35 and the trim coils and pole pieces installed on the surface of the main pole 35. These components that form the main magnetic field distribution are arranged symmetrically with respect to the orbital plane, so the main magnetic field, on the orbital plane, only has a magnetic field component perpendicular to the orbital plane. The radio frequency acceleration voltage frequency controller 23 may be configured as shown in Figure 4, and may include a variable capacitor 60 and a variable capacitor controller 61.

[0039] In this embodiment, a rotating capacitor is used as the variable capacitor 60. In this case, the variable capacitor control device 61 controls the rotation of the motor connected to the rotating capacitor, etc.

[0040] The circular accelerator 30 of this embodiment has a kicker coil 85, a radio frequency kicker 83, a septum coil 41, and a high energy beam transport line 45 as devices for extracting a beam.

[0041] The radio frequency kicker 83 is a device that applies a radio frequency voltage to the passing circulating beam, thereby further applying a dynamic magnetic field that kicks the charged particle beam circulating within the circular accelerator 30 into a region where a radio frequency disturbance electric field is generated.

[0042] Inside the main electromagnet 40, a pole magnetic field region 42 and a regenerator magnetic field region 43 are formed, which are high-frequency disturbance magnetic fields consisting of a dipole magnetic field or a multipole magnetic field.

[0043] The beam is extracted using a radio frequency kicker 83, a peeler magnetic field region 42, a regenerator magnetic field region 43, a septum coil 41, and a high energy beam transport line 45. The circulating beam reaches the position of the radio frequency kicker 83 by exciting the kicker coil 85.

[0044] Thereafter, a voltage is supplied from the RF extraction power supply 25 in response to a command from the RF extraction power supply controller 26, and a RF electric field is generated by the RF kicker 83 via the RF extraction voltage controller 24, which realizes the frequency specified by the RF extraction voltage frequency controller 27. This RF electric field increases the betatron oscillation amplitude of the beam. The beam, whose betatron oscillation amplitude has increased, eventually reaches the peeler magnetic field region 42 and the regenerator magnetic field region 43, which are located on the outer periphery of the maximum energy orbit 81 at a certain distance from the maximum energy orbit 81.

[0045] The beam that reaches the peeler magnetic field region 42 is kicked toward the outer periphery of the orbital plane, while the beam that reaches the regenerator magnetic field region 43 is kicked toward the inner periphery of the orbital plane. The kick from the quadrupole magnetic field component of the peeler magnetic field region 42 further increases the betatron oscillation amplitude of the beam, increasing the turn separation. At the same time, the magnetic field of the regenerator magnetic field region 43 prevents the beam from suddenly fluctuating in the horizontal direction, preventing the beam from being lost due to betatron oscillation diverging in the vertical direction, which is 90 degrees perpendicular to the horizontal direction, before it is extracted.

[0046] Once sufficient turn separation is obtained, the beam enters the septum coil 41, is kicked out of the orbital plane, passes through the high-energy beam transport line 45, and is extracted to the outside of the circular accelerator 30.

[0047] The increase in turn separation caused by the peeler magnetic field region 42 and the regenerator magnetic field region 43 is much greater than that caused by the radio frequency kicker 83. Therefore, by adjusting the radio frequency voltage applied by the radio frequency kicker 83, it is possible to adjust the amount of the beam that reaches the peeler magnetic field region 42 and the regenerator magnetic field region 43 out of the beam orbiting on the maximum energy orbit 81.

[0048] As a result, by stopping the application of radio frequency to the radio frequency kicker 83 during beam extraction, the beam will not reach the peeler magnetic field region 42 and the regenerator magnetic field region 43, and it becomes possible to interrupt the beam extraction from the circular accelerator 30. Similarly, by restarting the application of radio frequency to the radio frequency kicker 83, it is possible to resume the beam extraction.

[0049] Furthermore, by controlling the strength of the voltage applied to the high frequency kicker 83 or the amplitude, phase, or frequency of the high frequency, the strength of the beam emitted from the circular accelerator 30 can be controlled.

[0050] The beam that travels inside the septum coil 41 is deflected and transported to the high-energy beam transport line 45. Two or more septum coils 41 may be arranged in the beam traveling direction. If the beam can be transported by the magnetic field formed by the main electromagnet 40 alone, the septum coil 41 may not be necessary.

[0051] A high-energy beam transport system 45 for transporting the extracted beam from inside the main electromagnet 40 to outside is arranged next to the septum coil 41 , through the beam through-hole 44 and to the outside of the main electromagnet 40 .

[0052] The peeler magnetic field region 42 and the regenerator magnetic field region 43 are regions where a multipole magnetic field acting on the beam exists. This multipole magnetic field includes at least a quadrupole magnetic field component, and may include a multipole magnetic field of more than four poles, or even a bipole magnetic field. The peeler magnetic field region 42 has a magnetic field gradient that weakens the main magnetic field toward the radially outer periphery, while the regenerator magnetic field region 43 has a magnetic field gradient that strengthens the main magnetic field toward the radially outer periphery. Note that the peeler magnetic field region 42 can also be a region where the main magnetic field at the pole tip decreases.

[0053] The peeler magnetic field region 42 and the regenerator magnetic field region 43 are respectively arranged on the outer periphery of the maximum energy orbit 81 in azimuthal regions on either side of the beam extraction path entrance 82. Furthermore, it is desirable that the peeler magnetic field region 42 and the regenerator magnetic field region 43 be arranged on the outer periphery of the maximum energy orbit 81 with a distance greater than the amplitude of the betatron oscillation before resonance, so that the beam does not advance into the peeler magnetic field region 42 or the regenerator magnetic field region 43 before the betatron oscillation amplitude is increased by the high-frequency kicker 83.

[0054] It is also desirable to place the peeler magnetic field region 42 on the upstream side and the regenerator magnetic field region 43 on the downstream side in the beam traveling direction, but the reverse is also possible.

[0055] A plurality of magnetic pole pieces and / or coils made of magnetic material are fixed by a non-magnetic material near the peeler magnetic field region 42 and the regenerator magnetic field region 43 to form the desired multipole magnetic field. For example, for each of the peeler magnetic field region 42 and the regenerator magnetic field region 43, a multipole magnetic field is formed by the plurality of magnetic pole pieces and a dipole magnetic field is formed by the coils. The plurality of magnetic pole pieces and coils can be arranged close to each other or at spatially separated locations.

[0056] Figure 5 shows a flowchart of the process from when a beam of a certain energy is requested to be irradiated to the outside of the accelerator until the irradiation is completed.

[0057] After an irradiation request is made, the beam is accelerated to the required energy by beam acceleration (S71). The acceleration stops when the RF acceleration power supply control device 22 stops the voltage supply from the RF acceleration power supply 21 (S72), and the beam is accumulated in the accelerator.

[0058] In this embodiment, after the RF acceleration voltage is stopped 62, the RF acceleration voltage controller 20 determines the circulation frequency or kinetic energy of the charged particle beam circulating inside the circular accelerator 30 (S73), and the RF extraction voltage controller 24 generates a RF disturbance electric field in accordance with the determined circulation frequency or kinetic energy.

[0059] Here, in this embodiment, as specific examples of methods for determining the circulation frequency or kinetic energy of the charged particle beam circulating inside the circular accelerator 30, any of the following methods can be adopted: (1) determining by measuring the circulation frequency or kinetic energy, (2) determining the circulation frequency or kinetic energy based on a command value to the Dee electrode 12 that applies the high-frequency acceleration electric field, (3) determining the circulation frequency or kinetic energy based on the measured value of the high-frequency acceleration electric field, or (4) determining the circulation frequency or kinetic energy based on the time when the high-frequency acceleration electric field is stopped.

[0060] In the method (1), for example, the measurement electrode 84 in FIG. 2 is used to measure the rotational position or rotational frequency of the charged particle beam circulating inside the circular accelerator 30, and the radio frequency acceleration voltage control device 20 determines the rotational frequency or kinetic energy from the measured rotational position or rotational frequency.

[0061] In the method (2), the orbital frequency or kinetic energy is calculated from the command value of the high frequency acceleration voltage output to the high frequency acceleration power supply 21 immediately before the power supply is stopped. For example, the relationship between the minimum and maximum command values ​​and the orbital frequency or kinetic energy is calculated in advance, and the orbital frequency or kinetic energy is calculated by interpolating between the minimum and maximum command values.

[0062] In method (3), for example, when the RF acceleration voltage is stopped 62, the orbital frequency is calculated from the RF acceleration voltage generated by the RF acceleration power supply 21 immediately before the stop, and the kinetic energy is calculated from the rotation angle of the motor connected to the rotation capacitor. By expressing the RF acceleration voltage or the motor rotation angle as a function of the acceleration start time, the orbital frequency or the kinetic energy of the orbital beam can be calculated backward.

[0063] In the method (4), the orbital frequency or kinetic energy is obtained from the output timing of the command to stop the high frequency acceleration voltage 62 .

[0064] Preferably, the extraction frequency is changed (S75) by referring to the parameter (circulation frequency or kinetic energy) determined in S73 by any of the methods (1) to (4) above, and a kicker coil current is applied (S76) to realize the changed extraction frequency, thereby applying a high-frequency extraction electric field (S77).

[0065] Here, betatron oscillation has the property that its amplitude increases resonantly when the product of either the tune or the fractional part of the tune and the orbital frequency of the beam is approximately the same as the frequency of the applied high-frequency extraction voltage.

[0066] Therefore, the frequency of the high frequency emission voltage f ext is the horizontal tune of the maximum energy beam, ν r The decimal part of Δν r and the maximum energy beam rotation frequency f rev The product Δν r ×f rev As a result, the amplitude of the horizontal betatron oscillation continues to increase resonantly, and the beam eventually reaches the peeler magnetic field region 42 and the regenerator magnetic field region 43.

[0067] In addition, the frequency of the frequency voltage f ext The horizontal tune of the maximum energy beam is ν r and the maximum energy beam rotation frequency f rev The product of ν r×f rev It may be set to be equal to

[0068] The beam is kicked toward the outer periphery when it passes through the peeler magnetic field region 42, and is kicked toward the inner periphery when it passes through the regenerator magnetic field region 43. Since both the peeler magnetic field region 42 and the regenerator magnetic field region 43 have a magnetic field gradient in the radial direction, the amount of kick gradually increases as the beam makes multiple orbits, and the turn separation increases. In other words, 2ν r By utilizing the resonance condition of the betatron oscillation at .DELTA.=2, the turn separation can be increased.

[0069] When a turn separation that greatly exceeds the thickness of the coil conductor installed on the inner circumference of the septum coil 41 is obtained, the beam is guided into the septum coil 41, subjected to sufficient deflection, and guided to the high-energy beam transport line 45, where it is extracted.

[0070] Figure 6 shows the control chart for this embodiment. θrot is the rotation angle of the motor connected to the rotating capacitor. Here, the rotation speed is assumed to be constant, but it may be modulated. f rf is the frequency of the high-frequency acceleration voltage, which is an integer multiple of the motor rotation frequency. acc is the amplitude of the RF acceleration voltage, which is applied and stopped according to the required beam energy. In addition, the intensity may be modulated to adjust the RF bucket area. kicker is the kicker coil current required to reach the high frequency kicker 83, which becomes constant after a certain rise time due to the inductance of the coil.

[0071] At the same time, the high frequency emission voltage V rfk By applying a current of 1000 kJ / s, the horizontal betatron oscillation amplitude increases, and finally the beam is extracted from the accelerator, and the beam extraction current I ext It is measured as:

[0072] FIG. 7 shows an example of table data 69 used for parameter reference in this embodiment.

[0073] In this embodiment, based on the previously determined orbital frequency or kinetic energy, the frequency of the high-frequency disturbance electric field can be determined based on parameters referenced from the table data 69. More specifically, in the table data 69 of FIG. 7, the central energy K of the beam, the kicker coil current I required to reach the high-frequency kicker 83, kicker , the beam rotation frequency f rev , horizontal tune of the beam ν r are stored in the RF emission voltage control device 24, for example, in a linked state.

[0074] As a result, the beam kinetic energy to be applied to the calculated beam kinetic energy is calculated. Here, the beam central energy K is used as an index, but the beam circulating frequency f rev may be.

[0075] Also, when a high frequency kicker is applied, the horizontal tuning r When fluctuating, its minimum value ν rmin and the maximum value ν rmax By storing these as table data 69A and generating band noise based on them, more efficient beam extraction is expected.

[0076] Furthermore, instead of band noise, a high frequency emission voltage of any power spectrum may be applied through a function generator, etc. In this case, parameters required to express each spectrum are stored as table data 69.

[0077] In an accelerator such as this embodiment, the beam oscillates synchrotronically within the RF bucket, giving it a certain width relative to the energy of the central beam. This width depends on the width of the RF bucket in the energy direction, and further depends on the RF acceleration voltage V acc Therefore, the RF acceleration voltage V accBy storing the upper and lower limits of the kinetic energy of the beam as table data 69B as shown in FIG. 9, the kicker coil current and the frequency f of the RF extraction voltage that cover these energies can be determined. ext By determining this based on the table data 69 and 69A shown in FIG. 7 and FIG. 8, the beam extraction efficiency can be further improved.

[0078] Next, the effects of this embodiment will be described.

[0079] The circular accelerator 30 of the first embodiment of the present invention described above is a device that applies a static magnetic field that circulates a charged particle beam, a frequency-modulated radio-frequency acceleration electric field that accelerates the charged particle beam, and a radio-frequency disturbance electric field that emits the charged particle beam. After the radio-frequency acceleration electric field is stopped, the circular accelerator 30 determines the circular frequency or kinetic energy of the charged particle beam circulating inside the circular accelerator 30, and generates a radio-frequency disturbance electric field according to the determined circular frequency or kinetic energy.

[0080] In the past, the ratio of the RF acceleration electric field to the RF disturbance electric field was one to one, but in this invention, the orbital frequency or kinetic energy of the circulating charged particle beam after acceleration is calculated, and the RF disturbance electric field is generated according to the calculated orbital frequency or kinetic energy. Therefore, even if there is a frequency deviation, the betatron oscillation amplitude can be increased by a more appropriate RF disturbance electric field, thereby improving the final beam utilization efficiency.

[0081] Furthermore, a dynamic magnetic field is further applied to kick the charged particle beam circulating within the circular accelerator 30 into the region where the high-frequency disturbance electric field is generated, thereby realizing highly accurate extraction of the charged particle beam.

[0082] Furthermore, by measuring the orbital frequency or kinetic energy, by determining the orbital frequency or kinetic energy based on the command value to the dee electrode 12 and dummy dee electrode 13 that apply the radio frequency acceleration electric field, by determining the orbital frequency or kinetic energy based on the measured value of the radio frequency acceleration electric field, or by determining the orbital frequency or kinetic energy based on the time when the radio frequency acceleration electric field is stopped, it is possible to apply an accurate radio frequency acceleration voltage that is more suitable for the extraction of an orbiting charged particle beam.

[0083] Furthermore, by determining the frequency of the high frequency disturbance electric field based on parameters referenced from the table data 69 on the basis of the rotation frequency or kinetic energy, it is possible to realize rapid and accurate extraction of the charged particle beam.

[0084] <Example 2> An accelerator according to a second embodiment of the present invention will be described with reference to Figures 10 to 16. In this embodiment, the description of the same configuration as in the first embodiment will be omitted, and only the different configuration will be described.

[0085] The circular accelerator 30A of this embodiment shown in FIG. 10 is an eccentric orbit accelerator in which the orbit of the charged particle beam is eccentric in one direction from the center of the circular accelerator 30A, and the main magnetic field is formed so as to eccentrically move the beam toward the entrance 82 of the beam extraction path.

[0086] 11 and 12 show the cross-sectional configuration of the eccentric orbit accelerator. Structural changes from those in FIG. 2 include the shapes of the dee electrode 12A and dummy dee electrode 13A, and the shape of the acceleration gap 11A formed between them. Here, the center line is the line passing through the center of the circle of the acceleration region. The ion injection section 55A and the low-energy beam transport system 51A are located on the center line closer to the beam extraction path entrance 82 than the center of the acceleration region.

[0087] Although not shown for convenience of illustration, the shapes of the upper and lower opposing surfaces of the main pole 35A for forming a magnetic field, which will be described later, are also significantly different from those of the first embodiment.

[0088] The acceleration gap 11A formed between the dee electrode 12A and the opposing dummy dee electrode 13A is arranged along the isotropic phase line. More specifically, the dee electrode 12A has a hollow sector-like shape with its tip near the center of the concentric orbit and its radius along the isotropic phase line. The dummy dee electrode 13A is shaped to face the dee electrode 12A.

[0089] In the low-energy region of the beam, the orbit is close to a concentric orbit centered near the ion injection section 55A, as in a cyclotron, but orbits of higher energy are densely concentrated near the entrance 82 of the beam extraction path, and conversely, near the inner conductor 14, the orbits of each energy are spaced apart. The point where these orbits are densely concentrated is called the concentrated region, and the area where they are dispersed is called the dispersed region. By arranging the orbit in this way and extracting the beam near the concentrated region, the required beam kick can be reduced, making it easy to extract a beam with variable energy.

[0090] To achieve the above-described orbit configuration and to generate stable vibrations around the orbit, the accelerator of this embodiment creates a distribution in which the main magnetic field decreases radially outward by the shape of the main pole 35 and the trim coils and pole pieces installed on its surface. Furthermore, the main magnetic field is a constant value along the line of the designed orbit. Therefore, the designed orbit is circular.

[0091] Next, we will explain the beam extraction method. The beam is extracted using a radio-frequency kicker 83, which is installed near the convergence region where the beam orbits of all the extracted energies are converged, and the peeler magnetic field region 42, regenerator magnetic field region 43, septum coil 41, and high-energy beam transport line 45, which are located on both sides of the radio-frequency kicker 83.

[0092] In this embodiment, among the above elements used for extraction, the configuration of the radio frequency kicker 83 is different from that of the first embodiment. Also, the kicker coil 85 may be omitted. The beam extraction procedure is essentially the same as that described in the first embodiment, but by shifting the timing of cutting off the accelerating radio frequency voltage and the timing of starting to apply a radio frequency voltage to the radio frequency kicker 83 earlier, a beam of any energy can be extracted. By starting to apply a radio frequency voltage, the amplitude of the betatron oscillation of the beam of the desired energy is increased by the radio frequency kicker 83. Eventually, the beam reaches the peeler magnetic field region 42 and the regenerator magnetic field region 43 and is extracted.

[0093] 13 to 16 are respectively equivalent to Fig. 5 to Fig. 8, but for cases where the kicker coil 85 is not used in this embodiment. When the kicker coil 85 is applied to this embodiment, the same control and table data as those in Fig. 5 to Fig. 8 are used.

[0094] The other configurations and operations are substantially the same as those of the accelerator of the first embodiment, and the details are omitted here.

[0095] The accelerator according to the second embodiment of the present invention also provides substantially the same effects as those of the accelerator according to the first embodiment described above.

[0096] Furthermore, since the orbit of the charged particle beam is eccentric in one direction from the center of the circular accelerator 30A, the orbit of the orbiting beam is converged in the convergence region, and therefore the beam can be deflected to the extraction orbit with a smaller local magnetic field than in a non-converged orbit, making extraction extremely easy. In particular, since the spacing between the beam orbits in the convergence region is narrower than in the past, an ion beam of a predetermined energy can be stably and easily extracted even if the ion beam energy ranges widely.

[0097] Example 3 A particle beam therapy system according to a third embodiment of the present invention will be described with reference to Fig. 17. Fig. 17 is a diagram showing the overall configuration of the particle beam therapy system according to this embodiment.

[0098] The particle beam therapy device 150 of this embodiment shown in Figure 17 comprises the circular accelerator 30 shown in Example 1 or the circular accelerator 30A shown in Example 2, a rotating gantry 90, an irradiation device 92 including a scanning electromagnet, a treatment table 101, and a control device 91 that controls them.

[0099] In the particle beam therapy system 150, the beams extracted from the circular accelerators 30, 30A are transported to the irradiation device 92 by the rotating gantry 90. The transported ion beam is shaped in accordance with the affected area by the irradiation device 92 and by adjusting the beam energy, and a predetermined amount is irradiated onto the affected area of ​​the patient 100 lying on the treatment couch 101.

[0100] The irradiation device 92 incorporates a dose monitor and monitors the dose irradiated to each irradiation spot on the patient 100. Based on this dose data, the control device 91 calculates the required dose for each irradiation spot and uses this as input data for the accelerator control device 93. The accelerator control device 93 controls the injection, acceleration, and extraction of the charged particle beam in the circular accelerators 30 and 30A, and supplies a beam of the required dose and energy.

[0101] The configuration and operation of the circular accelerators 30 and 30A are substantially the same as those of the first and second embodiments described above, and the details thereof will be omitted.

[0102] <Other> It should be noted that the present invention is not limited to the above-described embodiment, and includes various modifications. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations.

[0103] It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment, or to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0104] The embodiment of the present invention may be in the following form.

[0105] (1) A circular accelerator that applies a static magnetic field for circulating a charged particle beam, a frequency-modulated radio-frequency acceleration electric field for accelerating the charged particle beam, and a radio-frequency disturbance electric field for emitting the charged particle beam, wherein the circular accelerator determines the rotation frequency or kinetic energy of the charged particle beam circulating inside the circular accelerator after the radio-frequency acceleration electric field is stopped, and generates the radio-frequency disturbance electric field in accordance with the determined rotation frequency or kinetic energy.

[0106] (2) In the circular accelerator described in (1), a dynamic magnetic field is further applied to kick the charged particle beam circulating within the circular accelerator into a region where the high-frequency disturbance electric field is generated.

[0107] (3) In the circular accelerator according to (1) or (2), the orbital frequency or the kinetic energy is determined by measuring it.

[0108] (4) In the circular accelerator described in any one of (1) to (3), the orbital frequency or the kinetic energy is calculated based on a command value to an accelerating electrode that applies the high-frequency accelerating electric field.

[0109] (5) In the circular accelerator according to any one of (1) to (4), the orbital frequency or the kinetic energy is determined based on a measurement value of the high-frequency accelerating electric field.

[0110] (6) In the circular accelerator according to any one of (1) to (5), the orbital frequency or the kinetic energy is calculated based on the time when the high frequency accelerating electric field is stopped.

[0111] (7) In the circular accelerator according to any one of (1) to (6), the frequency of the high-frequency disturbance electric field is determined based on the orbital frequency or the kinetic energy, and on parameters referenced from table data.

[0112] (8) In the circular accelerator according to any one of (1) to (7), the orbit of the charged particle beam is eccentric in one direction from the center of the circular accelerator.

[0113] (9) A particle beam therapy device comprising the circular accelerator described in any one of (1) to (8). [Explanation of symbols]

[0114] 10...Radio frequency acceleration cavity 11,11A…acceleration gap 12, 12A...Dee electrode (accelerating electrode) 13, 13A...Dummy Dee electrode (acceleration electrode) 14...Inner conductor 15...Outer conductor 20...High frequency acceleration voltage control device 21...High frequency acceleration power supply 22...High frequency acceleration power supply control device 23...High frequency acceleration voltage frequency control device 24...High frequency emission voltage control device 25...High frequency emission power supply 26...High frequency emission power supply control device 27...High frequency emission voltage frequency control device 30,30A...Circular accelerator 35,35A…Main magnetic pole 36...Cryostat 37…York 38...Main coil 40...Main electromagnet 41...Septum coil 42…Peeler magnetic field region 43...Regenerator magnetic field region 44...Beam penetration hole 45...High energy beam transport system 46…Resonance suppression magnetic field region 48...Coil through hole 49...Vacuum hole 50...High frequency through hole 51, 51A...Low energy beam transport system 53...Ion source 55, 55A...Ion injection section 56...Electrostatic inflector 60...Variable capacitor 61...Variable capacitor control device 69, 69A, 69B, 69C, 69D...Table data 80...Minimum energy orbital 81...Highest energy orbit 82...Beam exit path entrance 83...High frequency kicker 84...Measuring electrode 85...Kicker Coil 90...Rotating gantry 91...Control device 92…Irradiation device 93...Accelerator control device 100...patient 101…Treatment table 150…Particle beam therapy device

Claims

1. A circular accelerator that applies a static magnetic field that circulates a charged particle beam, a frequency-modulated high-frequency acceleration electric field that accelerates the charged particle beam, and a high-frequency disturbance electric field that ejects the charged particle beam, determining a rotation frequency of the charged particle beam circulating inside the circular accelerator or a kinetic energy of the charged particle beam after the radio frequency acceleration electric field is stopped; The high-frequency disturbance electric field is generated in accordance with the determined orbital frequency or kinetic energy. Circular accelerator.

2. 2. The circular accelerator according to claim 1, A dynamic magnetic field is further applied to kick the charged particle beam circulating within the circular accelerator into a region where the high-frequency disturbance electric field is generated. Circular accelerator.

3. 2. The circular accelerator according to claim 1, Obtained by measuring the orbital frequency or the kinetic energy Circular accelerator.

4. 2. The circular accelerator according to claim 1, The orbital frequency or the kinetic energy is calculated based on a command value to the accelerating electrode that applies the high-frequency accelerating electric field. Circular accelerator.

5. 2. The circular accelerator according to claim 1, The orbital frequency or the kinetic energy is calculated based on the measurement value of the high frequency acceleration electric field. Circular accelerator.

6. 2. The circular accelerator according to claim 1, The orbital frequency or the kinetic energy is calculated based on the time when the high frequency acceleration electric field is stopped. Circular accelerator.

7. 2. The circular accelerator according to claim 1, The frequency of the high-frequency disturbance electric field is determined based on the parameters referenced from table data, based on the orbital frequency or the kinetic energy. Circular accelerator.

8. 2. The circular accelerator according to claim 1, The orbit of the charged particle beam is eccentric in one direction from the center of the circular accelerator. Circular accelerator.

9. A circular accelerator according to any one of claims 1 to 8 is provided. Particle beam therapy equipment.

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