Circular accelerator, particle beam therapy system, and method for operating accelerator

Abstract

An acceleration system in a particle beam therapy system includes: an electrode for generating an electric field that has a component for kicking a beam on an orbit; and an interruption device 350 for interrupting an accelerated beam without transporting the beam to the downstream side. The electrode is controlled to extract a beam remaining in an accelerator 1, and the beam is interrupted by the interruption device 350. As a result, provided are a circular accelerator, a particle beam therapy system, and a method for operating an accelerator, which are capable of solving a particular problem that arises when energy is switched in a variable energy accelerator.

Description

Circular accelerator, particle beam therapy system, and accelerator operation method

[0001] The present invention relates to a circular accelerator for accelerating heavy ions such as protons and carbon ions, a particle beam therapy system, and an accelerator operation method.

[0002] Patent Document 1 describes a particle beam therapy system that is small, inexpensive, and easy to adjust, and that provides an accelerator for use in a particle beam therapy system that can obtain an irradiation beam suitable for particle beam therapy using a spot scanning method. The particle beam therapy system includes an accelerator that accelerates a charged particle beam to a predetermined energy and emits it, an irradiation device that emits the charged particle beam to an irradiation target, a beam transport system that has a bending electromagnet that deflects the charged particle beam and guides the charged particle beam emitted from the accelerator to the irradiation device, and a beam blocking device that is installed in the beam transport system and blocks the supply of the charged particle beam to the irradiation device, and the beam blocking device includes a blocking electromagnet installed upstream of the bending electromagnet in the direction of travel of the charged particle beam, and a beam dump installed downstream of the bending electromagnet in the direction of travel of the charged particle beam.

[0003] Patent Document 2 describes a variable energy accelerator that can control the extraction of a charged particle beam from a circular accelerator with high precision, in which a first high frequency wave is applied in a main magnetic field to accelerate the charged particle beam while increasing the orbital radius, and a second high frequency wave having a different frequency from the first high frequency wave is applied to a concentration region of the orbit of the charged particle beam inside the circular accelerator or on the maximum energy orbit of the charged particle beam to extract the charged particle beam.

[0004] Patent No. 4691576 Patent No. 7002952

[0005] In particle therapy, the cancer tumor to be irradiated is irradiated with an ion beam with an energy level that corresponds to the depth from the body surface. The kinetic energy of the ions, in the case of protons, is approximately 200 MeV per nucleon, and an accelerator is used to generate the ion beam.

[0006] In order to apply a predetermined dose to the affected area, there is a method such as spot scanning irradiation, which is a method of irradiating the affected area while scanning an ion beam with an electromagnet in accordance with the shape of the affected area, as described in Patent Document 1, for example.

[0007] In spot scanning irradiation, the affected area is divided into layers according to the depth from the body surface, and each layer is irradiated with an ion beam at a predetermined energy level according to the depth from the body surface.In addition, the beam output from the accelerator requires high reproducibility in the beam irradiation position and energy at the time of irradiation.

[0008] An example of an accelerator used in particle beam therapy is a synchrotron accelerator described in Patent Document 1. There are also several other types of accelerators, such as cyclotrons, synchrocyclotrons, and the variable energy accelerator described in Patent Document 2.

[0009] In particle beam therapy, it is necessary to irradiate a tumor to be irradiated with a beam without exceeding the allowable range of the irradiation dose predetermined in a treatment plan, etc. Patent Document 1 discloses a technology for spot scanning irradiation in which, in regard to delayed charges that are extracted from the accelerator at unintended timing when the spot is moved, one of the electromagnets in the transport system is excited to cause the delayed charge beam to collide with a damper at a later stage, thereby preventing irradiation of the affected area.

[0010] The technique described in the above-mentioned Patent Document 1 can also be applied to the variable energy accelerator described in Patent Document 2.

[0011] Here, a phenomenon unique to variable energy accelerators such as those described in Patent Document 2 is that after irradiation of a certain layer is performed and irradiation of a predetermined dose of beam is completed, the beam remains within the accelerator and continues to circulate.

[0012] When irradiating the next layer, this remaining beam will be extracted simultaneously with the beam of the desired energy and the beam of the previous energy that is not desired at that timing.However, since the remaining beam may affect the dose distribution, it is necessary to separate and discard the beam of the previous energy from the beam of the desired energy.

[0013] However, if the method described in Patent Document 1 is simply applied to the variable energy accelerator described in Patent Document 2, it is difficult to separate and discard only the beam of the previous energy, so a different method is desired to deal with the phenomenon unique to variable energy accelerators.

[0014] An object of the present invention is to provide a circular accelerator, a particle beam therapy system, and an accelerator operating method that can solve the specific problems that arise when switching energies in a variable energy accelerator.

[0015] The present invention includes multiple means for solving the above problems, and one example is a circular accelerator equipped with electrodes that generate an electric field with a component that kicks the beam in orbit, and a blocking device that blocks the accelerated beam without transporting it to a subsequent stage, where the electrodes are controlled to extract the beam remaining in the circular accelerator and the beam is blocked by the blocking device.

[0016] According to the present invention, it is possible to solve the specific problems that arise when switching energies in a variable energy accelerator. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0017] 1 is a diagram showing an outline of the overall configuration of a particle beam therapy system of an embodiment; FIG. 2 is a diagram showing an outline of the overall configuration of an accelerator of an embodiment; FIG. 3 is a diagram showing the internal structure of an accelerator of an embodiment; FIG. 4 is a diagram showing the relationship between beam energy during orbit and orbit frequency in an accelerator of an embodiment; FIG. 5 is a diagram showing a designed orbit shape in an accelerator of an embodiment; FIG. 6 is a diagram showing the relationship between beam energy during orbit and magnetic field on a designed orbit in an accelerator of an embodiment; FIG. 7 is a diagram showing an outline of a radio frequency mode excited in a dee electrode in an accelerator of an embodiment; FIG. 8 is a diagram showing a timing chart of each device during operation in a particle beam therapy system of an embodiment; FIG. 9 is a diagram showing connections of control devices in a particle beam therapy system of an embodiment; and FIG. 10 is a diagram showing a control flow in a particle beam therapy system of an embodiment.

[0018] Embodiments of the circular accelerator, particle beam therapy system, and accelerator operation method of the present invention will be described with reference to Figures 1 to 10. In the drawings used in this specification, identical or corresponding components are designated by identical or similar reference numerals, and repeated description of these components may be omitted.

[0019] First, the overall configuration of a particle therapy system 1000 will be described with reference to Fig. 1. Fig. 1 is a diagram showing the overall configuration of the particle therapy system 1000 of this embodiment.

[0020] The particle beam therapy system 1000 shown in FIG. 1 comprises an accelerator 1 having electrodes, accelerating a beam, and extracting it to the outside, a beam transport device 2 having a blocking device 350 that blocks the accelerated beam without transporting it to a downstream stage and transporting the beam extracted from the accelerator 1, an irradiation device 3, an overall control device 40 that controls the accelerator 1 and the beam transport device 2, an irradiation control device 50, a treatment plan database 60, and a treatment planning device 70.

[0021] In the particle beam therapy system 1000, a beam generated in an accelerator 1 is transported to an irradiation device 3 via a beam transport device 2. In the irradiation device 3, the beam position is controlled by the magnetic field of a scanning electromagnet, and the beam is irradiated onto a predetermined affected area of ​​a patient 5 lying supine on a treatment couch 4.

[0022] The treatment planning device 70 is a device that calculates and determines various control parameters related to the irradiation of the beam onto the patient 5 , and the created treatment plan is recorded in the treatment plan database 60 .

[0023] The overall control device 40 controls each device based on the treatment plan obtained from the treatment plan database 60. The overall control device 40 also determines the target energy to be accelerated based on the treatment plan and transmits predetermined command values ​​to each device.

[0024] While the patient 5 is being irradiated with the beam, the irradiation device 3 constantly measures the irradiated dose and outputs the measurement results to the irradiation control device 50. The irradiation control device 50 is a control device for monitoring the irradiation dose and irradiation position, and when irradiation of a certain spot with a predetermined planned dose is completed, irradiation of the next spot is started. By repeating this process, it is possible to impart a dose distribution specified in a treatment plan previously prepared by the treatment planning device 70 to an appropriate position and depth.

[0025] In this embodiment, as shown in FIG. 1, the beam transport system 2 has a blocking device 350 that blocks the beam extracted from the accelerator 1 without transporting it to the downstream side (irradiation system 3).

[0026] The blocking device 350 includes a beam blocking electromagnet, an excitation power supply for the beam blocking electromagnet, and a beam dump for discarding the beam components removed by the blocking electromagnet (all of which are omitted for convenience of illustration). The excitation power supply is connected to the blocking electromagnet. The overall control device 40 is connected to the excitation power supply and controls the excitation of the blocking electromagnet.

[0027] The beam transport device 2 is equipped with a beam blocking magnet, a bending magnet, a beam dump, and a quadrupole magnet, from the upstream side in the beam traveling direction. In this embodiment, the bending magnet and the beam dump are installed separately, but it is also possible to install the beam dump inside the bending magnet, with the iron core of the bending magnet also serving as a radiation shield. Installing the bending magnet and the beam dump separately improves maintainability.

[0028] There are two methods for using the blocking device 350 to turn the beam supplied to the irradiation device 3 on and off: one is to deflect unnecessary beam components with a bipolar magnetic field when the beam blocking electromagnet is excited and discard them in a beam dump, and the other is to supply only the beam components deflected by the bipolar magnetic field when the beam blocking electromagnet is excited to the irradiation device 3.

[0029] In the former configuration, the beam extracted from the accelerator 1 is deflected by a beam blocking magnet, causing the deflected unnecessary beam components to collide with a beam dump. In the latter configuration, the beam blocking magnet is energized to deflect the beam, and the deflected beam components are supplied to the irradiation device 3, and the excitation of the beam blocking magnet is stopped to cause the unnecessary beam components to collide with the beam dump, thereby stopping the supply of beam to the irradiation device 3. Of these, the former configuration has the advantage that the beam transport device 2 can be easily adjusted, while the latter has the advantage of being highly safe, since the supply of beam to the irradiation device 3 can be cut off without controlling other equipment in the event of an equipment abnormality.

[0030] Although the beam transport device 2 is shown equipped with a bending electromagnet and a quadrupole electromagnet, it is also possible to directly connect the accelerator 1 and the irradiation device 3. In this case, the interrupter 350 can be disposed in a vacuum duct provided between the accelerator 1 and the irradiation device 3. In other words, the vacuum duct can be considered as a transport device.

[0031] The accelerator 1 of this embodiment is a frequency-modulated variable energy accelerator. This accelerator is a circular accelerator that has a time-constant magnetic field as the main magnetic field and accelerates protons circulating in the main magnetic field by a radio-frequency electric field. Its appearance is shown in Figure 2.

[0032] The accelerator 1 of this embodiment is not limited to an eccentric orbit accelerator as shown in FIG. 2 etc., but may be, for example, a synchrocyclotron or a cyclotron.

[0033] As shown in Fig. 2, the accelerator 1 excites a main magnetic field in a region through which the accelerating and circulating beam passes (hereinafter referred to as a beam passing region 20 (see Fig. 3)) by using an electromagnet 11 that can be separated into upper and lower parts. The beam passing region 20 inside the electromagnet 11 is evacuated by a vacuum pump (not shown).

[0034] The electromagnet 11 is provided with a plurality of through-holes that connect the outside with the beam passing region 20. For example, various through-holes such as an extracted beam through-hole 111 for extracting the accelerated beam, coil connection through-holes 112 and 113 for extracting the coil conductor arranged in the electromagnet 11 to the outside, and a high-frequency power input through-hole 114 are provided on the upper and lower divided connection surfaces.

[0035] A radio frequency acceleration cavity 21 that forms an accelerating electric field for accelerating ions into an ion beam is installed through the radio frequency power input through hole 114. As will be described later, the radio frequency acceleration cavity 21 is equipped with an acceleration dee electrode 221 (see FIG. 3 ) and a rotary variable capacitor 212 (modulation unit) that modulates the frequency of the accelerating electric field.

[0036] At a position above the electromagnet 11 and offset from the center, there are installed an ion source 12 for supplying hydrogen ions, a beam injection through-hole 115 for guiding the beam extracted from the ion source 12 to the beam passing region 20, and a monitor 12a provided at the beam injection through-hole 115 for detecting the amount of beam extracted from the ion source 12. Ions are injected between the electromagnets 11 inside the accelerator 1 through the beam injection through-hole 115 and an injection section 130 (see FIG. 3 ). Electric power required for injecting ions into the beam passing region 20 is supplied to the injection section 130 from the outside through the beam injection through-hole 115.

[0037] Next, the internal structure of the accelerator 1 will be described with reference to Figures 2 and 3. Figure 3 shows the arrangement of the equipment when the electromagnet 11 is viewed from above, dividing the surface into upper and lower halves.

[0038] As shown in Fig. 2, the upper and lower parts of the electromagnet 11 each have a cylindrical return yoke 121 and a top plate 122, and as shown in Fig. 3, a cylindrical magnetic pole 123 is located inside the upper and lower parts. The beam passing region 20 described above is located within the cylindrical space sandwiched between the upper and lower opposing magnetic poles 123. The surfaces where the upper and lower magnetic poles 123 face each other in a mirror-symmetric manner are defined as magnetic pole surfaces. Furthermore, the surfaces sandwiched between the magnetic pole surfaces and equidistant from the upper and lower magnetic pole surfaces are called orbital planes.

[0039] In a recess formed between the magnetic pole 123 and the return yoke 121, an annular coil 13 is installed along the wall on the outer periphery of the magnetic pole 123. By passing a current through the coil 13, the upper and lower opposing magnetic poles 123 are magnetized, and a magnetic field is excited in the beam passing region 20 with a predetermined distribution, which will be described later.

[0040] The RF accelerating cavity 21 excites an accelerating RF electric field for accelerating ions in the accelerating gap 223 by a λ / 4 type resonance mode. A portion of the RF accelerating cavity 21 that is fixedly installed relative to the accelerator is defined as a dee electrode 221. The RF accelerating cavity 21 is installed through the RF power input through-hole 114, and forms the dee electrode 221 that surrounds a portion of the beam passing region 20.

[0041] The ions are accelerated by a radio frequency electric field excited in an acceleration gap 223, which is a region sandwiched between a dee electrode 221 and a ground electrode 222 arranged opposite the dee electrode 221. In order for the radio frequency electric field to be synchronized with the orbital frequency of the beam, the frequency of the radio frequency electric field must be an odd multiple of the orbital frequency of the beam. In this accelerator 1, the frequency of the radio frequency electric field is set to 1 time the orbital frequency of the beam.

[0042] In this accelerator 1, ions generated in the ion source 12 are extracted into the beam passing region 20 as low-energy ions by a voltage applied to the extraction electrode of the injection section 130. The injected ions are accelerated each time they pass through the acceleration gap 223 by a radio-frequency electric field excited by the radio-frequency acceleration cavity 21, and become a high-energy ion beam.

[0043] 3, two shims 311 for generating additional magnetic fields that excite quadrupole magnetic fields or multipole magnetic fields (such as sextupole and higher) and a disturbance RF electrode 313 for applying a RF electric field are installed in an electrically insulated state on a part of the magnetic pole face in order to extract the beam from the accelerator 1. An injection port for extraction is installed at one end of the magnetic pole face.

[0044] The disturbance high-frequency electrode 313 can apply a small amplitude radio frequency (RF) electric field (disturbance high frequency), which kicks the orbiting particles in the in-plane direction of the orbit, causing the particles to deviate from the designed orbit. The particles whose orbit deviates from the designed orbit pass near the additional magnetic field generating shim 311.

[0045] The magnetic field generated by the additional magnetic field generating shim 311 restricts the stable region of the horizontal motion of the ion beam circulating in the beam passing region 20, and introduces particles that have been kicked by the disturbance high frequency and moved out of the stable region into the extraction septum electromagnet 312. In the accelerator 1 of this embodiment, the pair of additional magnetic field generating shims 311 each generate a magnetic field of opposite polarity that is superimposed on the main magnetic field formed by the magnetic pole 123.

[0046] Applying a radio frequency voltage of an appropriate frequency to the radio frequency disturbance electrode 313 disturbs the beam, and according to a principle to be described later, it becomes possible to control the beam on / off in synchronization with the on / off of the RF electric field applied to the radio frequency disturbance electrode 313. Details of the additional magnetic field generating shim 311 and the radio frequency disturbance electrode 313 will be described later.

[0047] In the accelerator 1, the shapes and arrangements of the upper and lower magnetic poles 123, coil 13, shim 311 for generating an additional magnetic field, extraction septum electromagnet 312, and disturbance high-frequency electrode 313 are designed so that the in-plane component of the main magnetic field in the orbital plane is nearly zero, resulting in a symmetrical arrangement and current distribution with respect to the orbital plane.

[0048] As shown in FIG. 3 , the shapes of the magnetic pole 123, the dee electrode 221, the coil 13, and the disturbance high-frequency electrode 313 are symmetrical with respect to a line segment connecting the center of the high-frequency power input through hole 114 and the center of the coil connection through hole 112 when the accelerator 1 is viewed from the top.

[0049] Next, the orbit and movement of the beam circulating in the accelerator 1 of this embodiment will be described.

[0050] The beam is accelerated while circulating in the beam passing region 20. The minimum kinetic energy of the beam that can be extracted from the accelerator 1 of this embodiment is 70 [MeV] and the maximum is 235 [MeV]. The greater the kinetic energy, the smaller the beam circulation frequency becomes; a kinetic energy beam immediately after injection circulates in the beam passing region 20 at 76 [MHz], and a beam that has reached 235 [MeV] circulates at 59 [MHz]. The relationship between these energies and circulation frequencies is shown in Figure 4.

[0051] The beam trajectories for each energy are shown in Figure 5. In Figure 5, the outermost circular orbit has a radius of 0.497 m, corresponding to the orbit with the maximum energy of 252 MeV, and from there, 51 circular orbits are shown, divided by the magnetic rigidity modulus, down to 0 MeV. The dotted lines connect the same orbital phases of each orbit, and are called equal orbital phase lines.

[0052] As shown in Figure 5, in the accelerator 1 of this embodiment, the center of the beam's orbit (design orbit) moves in one direction within the orbital plane as the beam accelerates. As a result of the movement of the design orbit, there are areas where orbits of different kinetic energies are close to each other (regions where orbits converge) and areas where they are far from each other (regions where orbits diverge). In other words, the design orbit of the beam is eccentric.

[0053] If you connect the points on the design orbits where the design orbits are closest to each other, you get a line segment that is perpendicular to all of the design orbits. Also, if you connect the points on the design orbits where the design orbits are furthest apart, you get a line segment that is perpendicular to all of the design orbits, and these two line segments are on the same line. If you define this line as the axis of symmetry, the shape of the design orbit will be symmetrical with respect to a plane that passes through the axis of symmetry and is perpendicular to the orbital plane.

[0054] 5 are plotted at intervals of π / 20 rotation phase from the convergence region. The acceleration gap 223 formed between the dee electrode 221 and the ground electrode 222 facing the dee electrode 221 is set along the isotropic phase line that rotates ±90 degrees from the convergence point.

[0055] In order to achieve the above-mentioned orbit configuration and to generate stable oscillations around the orbit, the accelerator 1 of this embodiment has a main magnetic field distribution in which the magnitude of the magnetic field decreases toward the outside in the deflection radius direction of the designed orbit. In other words, the relationship between the beam energy and the average value of the magnetic field on the orbit is as shown in Figure 6.

[0056] The magnetic field distribution is such that the magnetic field on the orbit decreases as the beam energy increases, i.e., the magnetic field decreases on the outer radial side. Under such a magnetic field, betatron oscillations occur stably in both the radial direction within the orbital plane of the beam and in the direction perpendicular to the orbital plane. The magnetic field is constant along the designed orbit. As a result, the designed orbit becomes circular, and the orbital radius and orbital time increase as the beam energy increases.

[0057] In this system, particles that deviate slightly from the design orbit in the radial direction are subjected to a restoring force that returns them to the design orbit, and particles that deviate perpendicular to the orbital plane are also subjected to a restoring force from the main magnetic field in the direction that returns them to the orbital plane. In other words, if the magnetic field is appropriately reduced relative to the beam energy, particles that deviate from the design orbit will always be subjected to a restoring force in the direction that tries to return them to the design orbit, and will oscillate near the design orbit.

[0058] This allows the beam to circulate and accelerate stably. This oscillation around the design orbit is called betatron oscillation. In the accelerator 1 of this embodiment, as shown in Figure 6, the magnetic field reaches a maximum of 5 [T] at the injection section 130 and decreases to 4.91 [T] at the outermost periphery.

[0059] The above-mentioned main magnetic field distribution is excited by magnetizing the magnetic poles 123 by passing a predetermined excitation current through the coils 13. Furthermore, the shape of the magnetic poles 123 is symmetrical with respect to the orbital plane, and on the orbital plane, they only have a magnetic field component in a direction perpendicular to the orbital plane.

[0060] As described above, the RF accelerating cavity 21 excites an electric field in the acceleration gap 223. To this end, RF power is introduced from an external RF power source (a low-level RF generator 42 and a RF amplifier 43, see FIG. 9 ) through the input coupler 211, and a RF electric field is excited in the acceleration gap 223 between the dee electrode 221 and the ground electrode 222.

[0061] Generally, the electromagnetic field excited by a Dee electrode has a specific resonant frequency and spatial distribution determined by the electrode shape. An electromagnetic field with a specific frequency and spatial distribution is called an eigenmode, and there are multiple types of eigenmodes, and the mode excited for acceleration is called the fundamental mode.

[0062] The electromagnetic field distribution and surface current distribution in the fundamental mode are shown in Figure 7. In Figure 7, the outline of the resonator is shown by the thick line, the electric field distribution by the thick arrow (E), the magnetic field distribution by the dotted arrow (B), and the current distribution on the resonator surface by the solid arrow. In the fundamental mode, an electric field in phase with respect to the ground electrode 222 is generated everywhere in the gap from the dee electrode 221.

[0063] In the accelerator 1 of the present invention, the frequency of the electric field is modulated in response to the energy of the circulating beam in order to excite the radio frequency electric field in synchronization with the orbiting of the beam. In the radio frequency accelerating cavity 21 using the resonance mode as used in the present invention, it is necessary to sweep the radio frequency frequency over a range wider than the width of the resonance. To do this, it is also necessary to change the resonance frequency of the radio frequency accelerating cavity 21.

[0064] This control is performed by changing the capacitance of a rotary variable capacitor 212 installed at the end of the radio frequency accelerating cavity 21. The rotary variable capacitor 212 controls the capacitance generated between the external conductor and a conductor plate directly connected to the rotation axis 213 by the rotation angle of the rotation axis 213. In other words, the rotation angle of the rotation axis 213 is changed in accordance with the acceleration of the beam.

[0065] Next, the behavior of the beam from injection into the accelerator 1 of this embodiment to extraction will be described.

[0066] First, low-energy ions are output from the ion source 12, and the beam is guided to the beam passing region 20 via the beam injection through-hole 115 and the injection section .

[0067] The beam entering the beam passing region 20 is accelerated by the radio frequency electric field, and as its energy increases, the radius of rotation of its orbit also increases. The beam is then accelerated while the radio frequency electric field ensures stability in its traveling direction.

[0068] That is, the center of gravity of the beam does not pass through the acceleration gap 223 at the time when the radio frequency electric field is at its maximum, but passes through the acceleration gap 223 when the radio frequency electric field is decreasing over time. Then, since the frequency of the radio frequency electric field and the orbital frequency of the beam are synchronized at an integer multiple ratio, particles accelerated at a predetermined phase of the acceleration electric field are also accelerated at approximately the same phase in the next turn.

[0069] On the other hand, particles accelerated in a phase earlier than the acceleration phase are accelerated by a larger amount than particles accelerated in the acceleration phase, so they are accelerated in a delayed phase in the next turn. Conversely, particles accelerated in a phase later than the acceleration phase are accelerated by a smaller amount than particles accelerated in the acceleration phase, so they are accelerated in an advanced phase in the next turn.

[0070] In this way, particles whose timing is shifted from the specified acceleration phase move in the direction returning to the acceleration phase, and this action allows them to oscillate stably even within the phase plane (direction of travel) consisting of momentum and phase. This oscillation is called synchrotron oscillation. In other words, accelerating particles are gradually accelerated while oscillating in synchrotron oscillation, and reach the specified energy to be extracted. During stable synchrotron oscillation, individual particles rotate within a stable region on the phase plane called a radio frequency bucket.

[0071] In order to extract a specified extracted beam at a target energy, the RF electric field applied to the RF acceleration cavity 21 is gradually decreased, and the output from the external RF power supply is controlled by the overall control device 40 so that the amplitude of the RF electric field becomes approximately zero when the target energy is reached.

[0072] Through this process, the beam reaches a point near the target energy and then circulates stably. Then, a high frequency is applied to the disturbance high frequency electrode 313. The frequency of the high frequency corresponds to the frequency of the betatron oscillation of the beam, and the beam is disturbed in a manner that depends on its position in the traveling direction, i.e., on the time when it passes through the disturbance high frequency electrode 313.

[0073] Focusing on a specific particle, the disturbance electric field and the orbiting betatron oscillation frequency match, so they resonate, increasing the amplitude of the betatron oscillation of the particle. If the betatron oscillation amplitude continues to increase, the betatron oscillation suddenly diverges due to the effect of the kick magnetic field excited by the additional magnetic field generating shim 311 installed outside the designed orbit, displacing the beam outside the designed orbit. As a result, the particle is introduced into the extraction septum electromagnet 312. The boundary between this stable region and unstable region is called the separatrix.

[0074] Between the time when the target energy is reached and the time when the beam is extracted, the individual particles constituting the beam orbit in a phase space determined by the horizontal position and inclination of the beam, divided into a region where the beam can orbit stably and a region where the orbital deviation continues to increase unstably, by the quadrupole magnetic field and the multipole magnetic field of sextupole or more from the shim 311 for generating the additional magnetic field.

[0075] In accelerator 1, particles inside the separatrix continue to oscillate stably in betatron oscillation, but particles outside the separatrix are subjected to a kicking action by the shim 311 for generating the additional magnetic field, which accumulates with each revolution, causing large horizontal displacements relative to the designed orbit.

[0076] The particles that have undergone a large horizontal displacement are extracted out of the accelerator 1 along the extraction orbit 322 by a disturbance electric field created by the disturbance high-frequency electrode 313 (described later) and a magnetic field formed by the extraction septum electromagnet 312 on the extraction orbit 322 that has been installed in advance.

[0077] Furthermore, when the electric field applied to the disturbance RF electrode 313 is turned off, the increase in the betatron oscillation amplitude of the beam stops and the beam orbits within the stable region, so that extraction of the beam can be stopped.

[0078] The above describes the behavior of the beam from injection to extraction during one cycle, but the accelerator 1 repeats similar operations in subsequent cycles.

[0079] In other words, the accelerator 1 performs a pattern operation consisting of an injection process, an acceleration process, and an extraction process. The extraction process is completed when most of the circulating beam is extracted and it is determined that the remaining amount of circulating beam falls below a specified value, or when irradiation on a certain layer is completed. Once the extraction process is complete, the accelerator 1 returns to the injection process.

[0080] The next injection process starts when the rotation angle of the rotary variable capacitor 212 reaches a predetermined angle and the resonance frequency of the dee electrode 221 reaches a value suitable for beam injection.

[0081] Next, the most characteristic configuration and control of the accelerator 1 of the present invention will be described.

[0082] In a treatment plan determined by the treatment planning device 70, beams of multiple types of energy are usually irradiated onto the affected area of ​​the patient 5. In the particle beam therapy system 1000 of this embodiment, when beams of multiple types of energy are irradiated, the energy of the beams generated by the accelerator 1 is changed and the beams are sequentially irradiated onto the affected area.

[0083] When irradiation of a certain layer is completed and a different layer is to be irradiated next, the accelerator 1 generates a beam with an energy different from that in the previous operation.

[0084] In this case, if there is a beam remaining circulating in the accelerator 1 when irradiation of a certain layer is completed, and a beam with an energy corresponding to the next layer is accelerated as is, the beam with the previous energy will continue to remain, and two beams with different energies will be extracted during the extraction process. In this case, the delivered dose will be disturbed by the influence of the remaining beam with an energy corresponding to the previous layer. From another perspective, the delivered dose distribution when irradiating a certain layer will depend on the previous irradiation layer, and the reproducibility of the delivered dose distribution will be reduced.

[0085] To address this issue, the accelerator 1 discards the circulating beam when energy switching, i.e., layer switching, is performed.

[0086] For this reason, in this embodiment, the overall control device 40 controls, for example, the electrodes to extract the beam remaining in the accelerator 1 and controls the cutoff device 350 to cut off the beam.

[0087] For example, when switching the extracted beam from a first energy to a second energy different from the first energy, after the extraction of the first energy beam is completed, the overall control device 40 controls the blocking device 350 to bring it into a state where the beam can be blocked, and controls the electrodes to extract the first energy beam remaining in the accelerator 1.

[0088] In this case, it is desirable that the overall control device 40 executes extraction control for discarding the beam of the first energy in conjunction with switching the beam energy from the first energy to the second energy in the irradiation plan. In other words, it is desirable that discarding the beam of the first energy is always executed in conjunction with the energy change, regardless of whether or not there is a remaining beam.

[0089] The discarding method can be realized by exciting the blocking electromagnet of the blocking device 350 installed in the beam transport device 2 and extracting the beam in this state from the accelerator 1. In other words, the beam can be discarded by applying a high-frequency electric field to the disturbance high-frequency electrode 313 while the blocking electromagnet is excited. Of course, it is also possible to keep the blocking electromagnet of the blocking device 350 excited during normal irradiation, and stop the excitation when discarding, and discard the beam using a beam dump.

[0090] In order to extract the beam from the accelerator 1 for discarding, an extraction electric field is applied to the remaining beam by an electrode that generates an electric field component that kicks the orbiting beam. The accelerator 1 of this embodiment is provided with a plurality of electrodes for applying this extraction electric field to the remaining beam. The first is a disturbance RF electrode 313 that applies a disturbance electric field that kicks the orbiting beam in the in-plane direction of the orbit, and the second is a RF acceleration cavity 21 that applies an acceleration electric field that accelerates the orbiting beam.

[0091] To extract the beam using an accelerating electric field, the frequency of the accelerating electric field must match the betatron frequency of the beam. Because the frequency of the accelerating electric field is periodically modulated, almost the entire beam is discarded at a specific timing during the modulation period.

[0092] In this way, when there are multiple electrodes that apply the electric field for extraction, it is desirable for the overall control device 40 to determine the combination of electrodes to apply the electric field based on the operating cycle phase at the time extraction is completed and the amount of beam in orbit.

[0093] In this way, the energy consumption and the time required differ between destroying the beam with disturbing high frequency waves and destroying the beam with an accelerating electric field.

[0094] According to the characteristics of the accelerator 1 of this embodiment, it takes about 20 msec to extract the entire amount of the incident beam using the disturbance radio frequency, whereas when an accelerating electric field is used, the entire amount can be discarded in about 2 msec. On the other hand, the power consumption is about 1 kW for the former and about 100 kW for the latter. In other words, the power consumption increases when an accelerating electric field that can discard the beam at high speed is used.

[0095] Therefore, in order to discard the beam with as little power consumption as possible and in the shortest time possible, it is necessary to change the discarding method depending on the remaining amount of beam. Specifically, low-power, high-speed beam discarding can be achieved by predicting the remaining circulating beam amount from the balance between the dose irradiated until the completion of irradiation in a certain operating cycle and the amount of charge of the beam accelerated by the accelerator, and then selecting an appropriate discarding method. Alternatively, it is also possible to determine the method based on the amount of power consumption per unit time.

[0096] In this way, it is desirable that the overall control device 40 use the disturbance radio frequency electrode 313 when the remaining amount of the first energy beam in orbit is less than a specified amount, and use the radio frequency acceleration cavity 21 when it is equal to or greater than the specified amount.

[0097] The remaining amount of the first energy beam during rotation can be found from the difference between the output signal value relating to the beam amount from the ion source 12 of the beam in the accelerator 1 (the amount of ions supplied from the ion source 12) and the output signal value relating to the beam amount at the subsequent stage (the beam irradiation amount from the dose measuring device 3 a in the irradiation device 3), but it can also be measured directly as the beam current amount at the rotation position.

[0098] The series of processes described above, including beam injection, acceleration, extraction, and beam destruction, are shown in the timing chart of FIG. 8. As shown in FIG. 8, at a certain time t １ In the case where a beam of the first energy is irradiated up to the point where the first energy beam is irradiated and then a beam of the second energy is irradiated, the application of a high frequency electric field in the acceleration gap 223 or the application of a high frequency electric field for disturbance is performed at the timing when the irradiation of the beam of the first energy is completed.

[0099] Thereafter, control of the acceleration of the beam of the second energy is started after the extraction and discarding of the beam of the first energy remaining in the accelerator 1. For example, as control of the acceleration of the beam of the second energy, it is desirable to start applying an acceleration electric field (a radio frequency electric field in the acceleration gap 223) that accelerates the beam during orbit.

[0100] It is also possible to execute discard control immediately when it is determined that the energy will be switched, without predicting or measuring the remaining beam amount of the first energy.

[0101] A control block diagram for realizing the above processing is shown in Fig. 9. As shown in Fig. 9, a radio frequency power supply 46 is connected to the radio frequency disturbance electrode 313. The radio frequency power supply 46 is controlled by a radio frequency disturbance control device 47. Radio frequency power obtained by amplifying the radio frequency generated by a low-level radio frequency generator 42 is input to the radio frequency accelerating cavity 21 via a radio frequency amplifier 43. In addition, a motor control device 41 is connected to the servo motor 214, and it is controlled so as to rotate at a constant angular velocity.

[0102] The disturbance high-frequency control device 47, the low-level high-frequency generator 42, and the motor control device 41 control their controlled objects based on commands from the overall control device 40. The overall control device 40 controls each device based on a treatment plan acquired from the treatment plan database 60. The overall control device 40 also determines the target energy to be accelerated based on the treatment plan, and transmits predetermined command values ​​to each device.

[0103] Next, the process from the start to the end of irradiation is shown as a flowchart in FIG.

[0104] As shown in FIG. 10, after the start of irradiation, the overall control device 40 sets the acceleration energy (S101) and also sets the spot position (S102).

[0105] Next, the injection control of the beam from the ion source 12 and the acceleration control of the beam in the beam passing region 20 are performed (S103), and once acceleration to the predetermined energy is completed, i.e., once preparation for irradiation is completed, the beam irradiation control is performed (S104).

[0106] When the beam irradiation starts, the irradiation control device 50 receives a signal from the dose measurement device 3a in the irradiation device 3 and constantly monitors the irradiation dose and irradiation position. When irradiation of a predetermined spot is completed, the next spot is irradiated and irradiated (Yes in S105, S106).

[0107] In this embodiment, when irradiation of all spots on a layer is completed (Yes in S107), the overall control device 40 checks whether irradiation on the next layer, i.e., irradiation with a different energy level, is planned (S108). If it is determined that irradiation on the next layer, i.e., irradiation with a different energy level, is planned (No in S108), the overall control device 40 determines the beam discarding means described above (S109) and controls the target device based on the determination result to discard the beam. Then, the process returns to step S101, and new setting values ​​for irradiating the next layer are sent to each control device.

[0108] The above steps are repeated until irradiation is completed for all layers (Yes in S108), and then irradiation is completed.

[0109] The configuration and operating procedure of the accelerator 1 described above allows for the discarding of the beam in the accelerator when changing layers in the spot scanning irradiation method, thereby preventing the irradiation of an unnecessary beam when irradiating the next layer. This improves the accuracy and reproducibility of the dose distribution to be irradiated. Note that the irradiation method is not limited to the spot scanning irradiation method, and can also be suitably applied to a raster scanning irradiation method in which irradiation is continued without stopping the beam when moving between spots, or a line scanning irradiation method in which the beam is continuously moved while irradiating without stopping.

[0110] Next, the effects of this embodiment will be described.

[0111] The acceleration system of this embodiment described above includes electrodes that generate an electric field with a component that kicks the beam on orbit, and a cutoff device 350 that cuts off the accelerated beam without transporting it to the subsequent stage. The electrodes are controlled to extract the beam remaining in the accelerator 1, and the beam is cut off by the cutoff device 350.

[0112] By discarding the beam remaining in the accelerator 1 in this way, it is possible to solve the particular problem that occurs when switching energies in a variable energy accelerator.

[0113] Furthermore, when switching the extracted beam from the first energy to the second energy, after the extraction of the beam of the first energy is completed, the cutoff device 350 is controlled to be in a state where the beam can be cut off, and the electrodes are controlled to extract the remaining beam, thereby preventing the beam of the previous energy from being present in the accelerator 1 at the time of the next layer irradiation, thereby enabling further improvement in the accuracy of the irradiated dose distribution and irradiation with good reproducibility. In other words, deviation from the planned dose established at the time of planning can be reduced and reproducibility can be increased.

[0114] Furthermore, by providing an accelerator 1 having electrodes, which accelerates the beam and extracts it to the outside, a beam transport device having a cutoff device 350, which transports the beam extracted from the accelerator 1, and an overall control device 40 which controls the electrodes and the cutoff device 350 to extract the remaining beam, reliable and easy disposal can be achieved.

[0115] Furthermore, the overall control device 40 controls the extraction of the first energy beam in conjunction with the switching of the beam energy from the first energy to the second energy in the irradiation plan, which ensures that the remaining beam is discarded when the energy is switched, thereby further reducing the possibility of irradiating a beam other than the desired energy, thereby reducing deviation from the planned dose and increasing reproducibility.

[0116] Furthermore, multiple electrodes are provided, and the overall control device 40 determines the combination of electrodes to apply the electric field based on the operating cycle phase at the time extraction is completed and the amount of beam in circulation, thereby enabling the execution of discard control that is more in line with the purpose of the irradiation plan.

[0117] Furthermore, the electrodes are the disturbance radio frequency electrode 313 that applies a disturbance electric field that kicks the orbiting beam in the in-plane direction of the orbit, and the radio frequency acceleration cavity 21 that applies an acceleration electric field that accelerates the orbiting beam, so that discard control can be achieved without any new configuration.

[0118] Furthermore, the overall control device 40 uses the disturbance RF electrode 313 when the remaining amount of circulating beam is less than a specified amount, and uses the RF acceleration cavity 21 when the remaining amount is equal to or greater than the specified amount, thereby enabling more energy-efficient disposal or disposal in a shorter time depending on the remaining beam.

[0119] Furthermore, by determining the remaining amount from the difference between the output signal value relating to the beam amount from the beam generating device in the accelerator 1 and the output signal value relating to the beam amount at the subsequent stage, more appropriate discarding operations can be realized according to the situation.

[0120] Furthermore, after the extraction of the first energy beam remaining in the accelerator 1 is completed, the overall control device 40 starts controlling the acceleration of the second energy beam. In particular, as control of the acceleration of the second energy beam, by starting to apply an accelerating electric field that accelerates the circulating beam, it is possible to more reliably achieve acceleration of the second energy beam when no first energy beam remains.

[0121] <Others> The present invention is not limited to the above-described embodiments, and various modifications and applications are possible. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations.

[0122] For example, the present invention may be in the following form.

[0123] (1) A circular accelerator having electrodes that generate an electric field with a component that kicks a beam in orbit, and a blocking device that blocks the accelerated beam without transporting it to a subsequent stage, in which the electrodes are controlled to extract the beam remaining in the circular accelerator and the beam is blocked by the blocking device.

[0124] (2) In the circular accelerator described in (1), when the extracted beam is switched from the first energy to the second energy, after the extraction of the beam of the first energy is completed, the blocking device is controlled to make the beam capable of being blocked, and the electrode is controlled to extract the remaining beam.

[0125] (3) In the circular accelerator described in (1) or (2), an accelerator device having the electrodes, which accelerates the beam and extracts it to the outside, a beam transport device having the cutoff device, which transports the beam extracted from the accelerator device, and a control device which controls the electrodes and the cutoff device to extract the remaining beam.

[0126] (4) In the circular accelerator described in (3), the control device executes control to extract the beam of the first energy in conjunction with switching the energy of the beam from the first energy to the second energy in the irradiation plan.

[0127] (5) In the circular accelerator described in (3) or (4), a plurality of the electrodes are provided, and the control device determines the combination of the electrodes to which the electric field is applied based on the operation cycle phase at the time when extraction is completed and the amount of beam in circulation.

[0128] (6) In the circular accelerator described in (5), the electrodes are disturbance electrodes that apply a disturbance electric field that kicks the orbiting beam in the in-plane direction of the orbit, and acceleration electrodes that apply an acceleration electric field that accelerates the orbiting beam.

[0129] (7) In the circular accelerator described in (6), the control device uses the disturbance electrode when the remaining amount of the beam during rotation is less than a specified amount, and uses the acceleration electrode when the remaining amount is equal to or greater than the specified amount.

[0130] (8) In the circular accelerator described in (7), the remaining amount is calculated from the difference between the output signal value relating to the beam amount from a beam generating device in the accelerator and the output signal value relating to the beam amount on the downstream side.

[0131] (9) In the circular accelerator described in any one of (3) to (8), the control device starts controlling the acceleration of the beam of the second energy after the extraction of the beam of the first energy remaining in the accelerator is completed.

[0132] (10) In the circular accelerator described in (9), the control device controls the acceleration of the beam of the second energy by starting application of an accelerating electric field that accelerates the beam during orbit.

[0133] (11) In the circular accelerator according to any one of (1) to (10), the accelerator device is capable of continuously accelerating and extracting the beams having different energies.

[0134] (12) A particle beam therapy system including the circular accelerator according to any one of (1) to (11).

[0135] REFERENCE SIGNS LIST 1...Accelerator (accelerating device) 2...Beam transport device 3...Irradiation device 3a...Dose measuring device 4...Treatment couch 5...Patient 11...Electromagnet 12...Ion source (beam generating device) 12a...Monitor 13...Coil 20...Beam passing area 21...Radio frequency acceleration cavity (electrode, accelerating electrode) 40...Overall control device (control device) 41...Motor control device 42...Low level radio frequency generator 43...Radio frequency amplifier 46...Radio frequency power supply 47...Radio frequency disturbance control device 50...Irradiation control device 60...Treatment plan database 70...Treatment planning device 111...Through-hole for extracted beam 112, 113...Through-hole for coil connection 114...Through-hole for radio frequency power input 115...Through-hole for beam injection 121...Return yoke 122...Top plate 123...Magnetic pole 130...Injection section 211...Input coupler 212...Rotary variable capacitance capacitor 213... Rotating shaft 214... Servo motor 221... Dee electrode 222... Ground electrode 223... Acceleration gap 311... Shim for generating additional magnetic field 312... Extraction septum electromagnet 313... Disturbance high frequency electrode (electrode, disturbance electrode) 322... Extraction orbit 350... Interrupter 1000... Particle beam therapy system

Claims

1. A circular accelerator comprising electrodes that generate an electric field with components that kick a beam in orbit, and a blocking device that blocks the accelerated beam without transporting it to a downstream stage, wherein the electrodes are controlled to extract the beam remaining within the circular accelerator and the beam is blocked by the blocking device.

2. A circular accelerator as claimed in claim 1, wherein when the extracted beam is switched from a first energy to a second energy, after extraction of the beam of the first energy is completed, the cutoff device is controlled to bring the beam into a state where it can be cut off, and the electrode is controlled to extract the remaining beam.

3. A circular accelerator as claimed in claim 2, comprising: an accelerator having the electrodes, which accelerates the beam and extracts it to the outside; a beam transport device having the cutoff device, which transports the beam extracted from the accelerator; and a control device which controls the electrodes and the cutoff device to extract the remaining beam.

4. A circular accelerator according to claim 3, wherein the control device executes control to extract the beam of the first energy in conjunction with switching of the beam energy from the first energy to the second energy in an irradiation plan.

5. A circular accelerator according to claim 3, wherein a plurality of the electrodes are provided, and the control device determines the combination of the electrodes to which the electric field is applied based on the operation cycle phase at the time extraction is completed and the amount of beam in circulation.

6. A circular accelerator according to claim 5, wherein the electrodes are disturbance electrodes that apply a disturbance electric field that kicks the orbiting beam in the in-plane direction of the orbit, and acceleration electrodes that apply an acceleration electric field that accelerates the orbiting beam.

7. A circular accelerator according to claim 6, wherein the control device uses the disturbance electrodes when the remaining amount of the circulating beam is less than a specified amount, and uses the acceleration electrodes when the remaining amount is equal to or greater than the specified amount.

8. A circular accelerator according to claim 7, wherein the remaining amount is determined from the difference between an output signal value relating to the beam amount from a beam generating device within the accelerator and an output signal value relating to the beam amount at the rear stage.

9. A circular accelerator according to claim 3, wherein the control device starts controlling the acceleration of the beam of the second energy after the beam of the first energy remaining in the accelerator has been extracted.

10. A circular accelerator according to claim 9, wherein the control device controls the acceleration of the beam of the second energy by starting application of an accelerating electric field that accelerates the beam during orbit.

11. A circular accelerator according to claim 1, wherein the accelerator device is capable of continuously accelerating and extracting the beams having different energies.

12. A particle beam therapy system comprising the circular accelerator according to any one of claims 1 to 11.

13. A method for operating a circular accelerator comprising electrodes that generate an electric field with a component that kicks a beam in orbit, and a blocking device that blocks the accelerated beam without transporting it to a downstream stage, the method comprising controlling the electrodes to extract the beam remaining in the circular accelerator and blocking it with the blocking device.

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