JP2023122453A - Accelerator and particle beam therapy system including the same - Google Patents

Abstract

To provide an accelerator that can efficiently generate a beam and a particle therapy system including the same.SOLUTION: A circumferential orbit type accelerator generates a beam by accelerating ions supplied from an ion source by a main magnetic field and a frequency modulated high-frequency electric field. The circumferential orbit type accelerator includes an acceleration high-frequency application device that is capable of frequency modulation and applies an acceleration high frequency wave to accelerate ions, an extraction high-frequency application device that applies an extraction high-frequency wave for extracting a beam at a frequency different from the acceleration high-frequency wave, a disturbance magnetic field area forming part that forms a disturbance magnetic field area, and a septum magnet for extracting the beam. While the beam is being extracted, new ions are supplied from an ion source and accelerated (Figs.11(1)-(8)).SELECTED DRAWING: Figure 11

Description

The present invention relates to an accelerator and a particle beam therapy system comprising the accelerator.

High-energy ion beams used in particle beam therapy and physical experiments are generated using accelerators. There are several types of accelerators that obtain beams with a kinetic energy of around 200 MeV per nucleon. For example, a cyclotron, a synchrotron, a synchrocyclotron as described in Patent Document 1, and a variable energy accelerator as described in Patent Document 2 are known. A feature of cyclotrons and synchrocyclotrons is that they accelerate a beam circulating in a static magnetic field with a high-frequency electric field. In cyclotrons and synchrotrons, the beam increases the radius of curvature of its trajectory as it is accelerated, moves to outer trajectories, reaches maximum energy and is then extracted. Therefore, the energy of the extracted beam is basically fixed.

In the synchrocyclotron of Patent Document 1, a pair of ferromagnetic poles having a substantially circular cross section with a radius R are arranged vertically with the median plane interposed therebetween with their central axes aligned. A pair of poles are separated by a gap that defines a cavity having a substantially symmetrical profile with respect to the median plane. The height of the gap varies in the radial direction of the pole. The height of the gap is Hcenter at the center axis, and in the circular portion from the center axis to the radius R2, the height gradually increases from Hcenter as the radius increases, reaching a maximum value Hmax at the radius R2. The annular portion larger than the radius R2 gradually decreases in gap height as the radius increases, and the gap height at the edge of the pole is Hedge. A synchrocyclotron with such a gap-shaped cavity is disclosed in US Pat. No. 6,300,000 to minimize the size of the synchrocyclotron while minimizing the magnetic field in the gap.

Patent Document 2 discloses an orbital accelerator that accelerates a beam by a main magnetic field and a frequency-modulated high-frequency electric field as a compact accelerator capable of extracting a beam of variable energy, and is capable of frequency modulation. an acceleration high-frequency applying device for applying an accelerating high-frequency wave for accelerating the beam; an extracting high-frequency applying device for applying an extracting high-frequency wave having a different frequency from the accelerating high-frequency wave for extracting the beam; and a magnetic field having a number of poles of two or more. and a septum electromagnet having a magnetic shim and a septum coil. Accelerators are described.

Japanese Patent Publication No. 2013-541170 JP 2020-38797 A

In particle beam therapy, it is required to irradiate a tumor to be irradiated with a beam without exceeding an allowable range of irradiation dose predetermined in a treatment plan or the like. In the particle beam therapy system using the synchrocyclotron of Patent Document 1, it is necessary to make the amount of beam that can be accelerated and extracted within one operation cycle of the synchrocyclotron sufficiently smaller than the allowable range of irradiation dose. Therefore, in Patent Document 1, the amount of charge accelerated in one operation cycle must be smaller than the upper limit determined by the performance of the accelerator, and it takes time to complete the irradiation.

Since the energy of the extracted beam is variable in the variable energy accelerator of Patent Document 2, it is possible to emit a beam with an energy that matches the irradiation dose determined in the treatment plan. Therefore, the variable energy accelerator can shorten the beam irradiation time of particle beam therapy compared to the synchrocyclotron. The variable energy accelerator is equivalent in accelerator size to cyclotrons and synchrocyclotrons, and is small. Therefore, the variable energy accelerator is expected to further shorten the beam irradiation time as an accelerator of a particle beam therapy system. However, in the accelerator operation method described in Patent Document 2, the accelerator operates in a cycle of about several milliseconds. During this cycle, an ion beam (hereafter referred to as a beam) is extracted during the period during which ions are injected from the ion source into the accelerator, the period during which the ions are accelerated, and the period from when all the injected ions are irradiated until they are injected again. I can't.

An object of the present invention is to provide an accelerator capable of efficiently generating beams and a particle beam therapy system equipped with the accelerator.

In order to solve the above problems, an accelerator according to the present invention is an orbital accelerator that accelerates ions supplied from an ion source to generate a beam by means of a main magnetic field and a frequency-modulated high-frequency electric field. An acceleration high-frequency applying device for applying an accelerating high-frequency wave for accelerating ions, an extraction high-frequency applying device for applying a high-frequency wave for extracting a beam at a frequency different from the accelerating high-frequency wave, and a disturbing magnetic field region. A stray magnetic field region forming portion to form and a septum electromagnet for beam extraction are provided, and new ions are supplied from the ion source and accelerated during beam extraction.

According to the present invention, beams can be efficiently generated and extracted.

1 is an overall schematic diagram of an accelerator of Example 1. FIG. Internal structure of the accelerator. FIG. 10 is a diagram showing the relationship between beam energy during circulation and circulation frequency. Explanatory drawing of a design track|orbit shape. FIG. 11 is a diagram showing the relationship between the beam energy during orbit and the design on-orbit magnetic field. Schematic diagram of high frequency modes excited in the Dee electrode. Schematic diagram of a high frequency bucket. Explanatory drawing which shows the phase space just before the end of acceleration. Explanatory drawing which shows the phase space immediately after the completion|finish of acceleration. Accelerator control block diagram. Timing chart of accelerator operation. 4 is a flowchart showing control processing of an accelerator; 4 is a flowchart of processing for measuring beam amount; FIG. 10 is a structural example of a high-frequency cavity according to Example 3; FIG. Overall configuration diagram of a particle beam therapy system.

The accelerator will be described below with reference to the drawings. In this embodiment, temporally serial processes of injection of ions (output of ions), acceleration of injected ions, extraction of accelerated ions (beam), and deceleration are executed in parallel. do. In this embodiment, the injection process and the acceleration process are repeatedly performed to maintain a state in which the beam corresponding to the irradiation energy is constantly replenished in the accelerator. As a result, in this embodiment, the injection process, the acceleration process, and the extraction process can be executed in parallel, so that the time during which the beam cannot be irradiated can be shortened and the efficiency can be improved.

Furthermore, in the particle beam therapy system equipped with the accelerator described in this embodiment, it is possible to reduce the time during which irradiation is not possible in terms of accelerator control, increase the proportion of time during which beam irradiation is possible, and increase the treatment time. can be shortened.

1 to 13, the accelerator 1 according to the present embodiment includes a high-frequency acceleration cavity 21 that forms an acceleration electric field for accelerating ions, and a rotary variable cavity for modulating the frequency of the acceleration electric field. An additional magnetic field generating shim 311 that gives a kick action from the stable region to the ions orbiting by the magnetic field formed by the capacitance capacitor 212 and the magnetic pole 123, and the ions given the kick action by the additional magnetic field generating shim 311 are transferred to the accelerator. 1, a low-level high-frequency generator 42 for controlling the accelerating electric field, and a high-frequency disturbance control device 47 for controlling the electric field for disturbance. A plurality of annular circulating trajectories of ions, each circulating, has a converging region and a discrete region, and ions injected in different cycles circulate at the same time with approximately the same energy.

A first embodiment will be described with reference to FIGS. 1 to 13. FIG. The accelerator 1 of this embodiment is a frequency modulated variable energy accelerator. This accelerator has a temporally constant magnetic field as its main magnetic field, and is a circular accelerator that accelerates protons orbiting in the main magnetic field by a high-frequency electric field. Its appearance is shown in FIG.

As shown in FIG. 1, the accelerator 1 uses electromagnets 11 that can be divided vertically to generate a main magnetic field in a region through which the beam passes during acceleration and circling (hereinafter referred to as a beam passage region 20 (see FIG. 2)). Excite. Electromagnet 11 is an example of a "pair of magnets." The inside of the electromagnet 11 is evacuated by a vacuum pump (not shown).

The electromagnet 11 is provided with a plurality of through holes for connecting the beam passing region 20 to the outside. For example, through-hole 111 for extraction beam for taking out the accelerated beam, through-holes 112 and 113 for drawing out the coil conductor arranged in electromagnet 11 to the outside, through-hole 114 for high-frequency power input, etc. Through holes are provided on the upper and lower split connection surfaces of the electromagnet 11 .

A high-frequency acceleration cavity (acceleration electrode) 21 is installed through the high-frequency power input through-hole 114 to form an acceleration electric field for accelerating ions into an ion beam. As will be described later, the high-frequency acceleration cavity 21, which is an example of the "high-frequency acceleration applying device", includes a dee electrode 221 for acceleration (see FIG. 2) and a rotary variable capacitor for modulating the frequency of the electric field for acceleration. A capacitor (modulation unit) 212 is installed.

An ion source 12 for supplying hydrogen ions is installed at an off-center position above the electromagnet 11 . The ion source 12 injects ions between the electromagnets 11 inside the accelerator 1 through the beam injection through-hole 115 and the injection section 130 (see FIG. 2). Electric power necessary for injecting ions into the beam passing region 20 is supplied from the outside to the injection section 130 through the through hole 115 .

The internal structure of the accelerator 1 will be described with reference to FIGS. 1 and 2. FIG. FIG. 2 is a diagram showing the arrangement of equipment when a plane obtained by dividing the electromagnet 11 into upper and lower parts is viewed from above.

As shown in FIG. 1, the upper and lower portions of the electromagnet 11 each have a cylindrical return yoke 121 and a top plate 122, and a cylindrical magnetic pole 123 is provided inside them, as shown in FIG. have. The beam passing region 20 described above is present in the cylindrical space sandwiched by the magnetic poles 123 facing each other vertically. A surface where the upper and lower magnetic poles 123 face each other is defined as a magnetic pole surface. A plane sandwiched between magnetic pole faces and parallel to the magnetic pole face and equidistant from the upper and lower magnetic pole faces is called a track surface.

In the recess formed between the magnetic pole 123 and the return yoke 121, the annular coil 13 is installed along the wall on the outer peripheral side of the magnetic pole 123. As shown in FIG. When a current is passed through the coil 13 , the magnetic poles 123 facing up and down are magnetized, and a magnetic field is excited in the beam passing region 20 with a predetermined distribution, which will be described later.

The RF acceleration cavity 21 excites an acceleration RF electric field for accelerating ions into the acceleration gap 223 by a λ/4 type resonance mode. A portion of the high-frequency acceleration cavity 21 that is fixedly installed with respect to the accelerator 1 is defined as a Dee electrode 221 . The high frequency acceleration cavity 21 forms a dee electrode 221 surrounding a partial area of the beam passage area 20 through the through hole 114 . Ions are accelerated by a high-frequency electric field excited by an acceleration gap 223 which is a region sandwiched between a Dee electrode 221 and a ground electrode 222 arranged to face the Dee electrode 221 . In order to synchronize with the aforementioned beam's circling frequency, the frequency of the high-frequency electric field needs to be an integer multiple of the beam's circulating frequency. In the accelerator 1, the frequency of the high-frequency electric field is one times the circulating frequency of the beam.

The magnetic pole 123 is provided with a plurality of trim coils 33 for fine adjustment of the magnetic field. The trim coil 33 is connected to an external power source through through holes 112 and 113 . By adjusting the excitation current for each system, the trim coil current is adjusted before operation so as to approximate the distribution of the main magnetic field described later and realize stable betatron oscillation.

In the accelerator 1 described above, ions generated by the ion source 12 are extracted to the beam passage region 20 in the state of low-energy ions by a voltage applied to the extraction electrode of the injection section 130 . The injected ions are accelerated by the high-frequency electric field excited by the high-frequency acceleration cavity 21 each time they pass through the acceleration gap 223 to form an ion beam.

As shown in FIG. 2, in order to extract the beam from the accelerator 1, two additional magnetic field generating shims (kick portions) 311 for exciting a quadrupole magnetic field or a multipolar magnetic field of six or more poles and a high-frequency electric field are applied. A disturbance electrode (disturbance portion) 313 is provided in an electrically insulated state on a part of the magnetic pole face. An incident part of the extraction septum electromagnet 312 is installed at one of the ends of the magnetic pole face.

The perturbation electrode 313 can apply a small amplitude radio frequency (RF) electric field that kicks the orbiting particles in the plane of their trajectories, causing them to deviate from their designed trajectories. Particles whose trajectories deviate from the designed trajectory pass near the additional magnetic field generating shim 311 .

The magnetic field generated by the additional magnetic field generating shim 311 restricts the stable region of the ion beam circulating in the beam passing region 20 and introduces the particles outside the stable region to the extraction septum electromagnet 312 . The pair of additional magnetic field generating shims 311 superimpose and excite magnetic fields of opposite polarities on the main magnetic field formed by the magnetic poles 123 .

When the beam is disturbed by applying a high-frequency voltage of an appropriate frequency to the disturbing electrode 313, the beam is turned on/off in synchronization with the on/off of the RF electric field applied to the disturbing electrode 313 according to the principle described later. /OFF control becomes possible. Details of the additional magnetic field generating shim 311 and the disturbance electrode 313 will be described later.

The upper and lower magnetic poles 123, the coil 13, the trim coil 33, the additional magnetic field generating shim 311, the extraction septum electromagnet 312, and the disturbance electrode 313 are shaped and arranged so that the in-plane component of the main magnetic field is approximately 0 on the orbital plane. is designed, and has a symmetrical arrangement and current distribution with respect to the orbital plane. The magnetic pole 123, the dee electrode 221, the coil 13, the trim coil 33, and the disturbance electrode 313 are shaped so that, as shown in FIG. The shape is symmetrical with respect to the line segment connecting the center of the

The trajectory and motion of the beam orbiting inside the accelerator 1 will be described. The beam is accelerated while circulating in the beam passing area 20 . The kinetic energy of the beam that can be extracted from the accelerator 1 is 70 MeV minimum and 235 MeV maximum. The higher the kinetic energy, the lower the circulating frequency of the beam. The beam of kinetic energy immediately after incidence circulates in the beam passing region 20 at 76 MHz, and the beam reaching kinetic energy of 235 MeV at 59 MHz. The relationship between these energies and the circulating frequency is as shown in FIG. The vertical axis in FIG. 3 indicates the lap frequency, and the horizontal axis in FIG. 3 indicates the kinetic energy.

As shown in FIG. 5, the formed magnetic field has a uniform distribution along the beam trajectory and the magnetic field decreases as the energy increases. That is, a magnetic field is formed such that the magnetic field on the radially outer side is reduced. Under such a magnetic field, the betatron oscillates stably in each of the radial direction in the orbital plane of the beam and the direction perpendicular to the orbital plane.

FIG. 4 shows the trajectory of each energy. A plurality of orbits are shown in FIG. In FIG. 4, there is a circular orbit with a radius of 0.497 m corresponding to the orbit with the maximum energy of 252 MeV on the outermost side, and from there, a total of 51 circular orbits are shown, which are divided into 51 by the magnetic rigidity up to the energy of 0 MeV. . A dotted line is a line connecting the same orbital phases of each orbit, and this line is called an isometric phase line.

As shown in FIG. 4, in the accelerator 1, the orbital center (designed orbit) of the beam moves in one direction within the orbital plane as the beam is accelerated. As a result of the movement of the design trajectory, there are places where trajectories with different kinetic energies are close to each other (regions where the loop trajectories converge) and regions where they are far from each other (regions where the loop trajectories are discrete). That is, the design trajectory of the beam is eccentric.

A line segment orthogonal to all the design trajectories is obtained by connecting each point of the design trajectories where the design trajectories are closest to each other. A line segment orthogonal to all the design trajectories is obtained by connecting points of the design trajectories that are farthest apart from each other. These two line segments are on the same straight line. If this straight line is defined as the axis of symmetry, the shape of the design raceway passes through the axis of symmetry and is symmetrical with respect to a plane perpendicular to the raceway surface.

The isochronous phase lines shown in FIG. 4 are plotted for each cyclic phase π/20 from the aggregated region. An acceleration gap 223 formed between the Dee electrode 221 and the ground electrode 222 facing the Dee electrode 221 is set along an equicircular phase line that rotates ±90 degrees when viewed from the consolidation point.

In order to generate the above-described orbit configuration and stable oscillation around the orbit, the accelerator 1 has a main magnetic field distribution in which the magnitude of the magnetic field decreases toward the outside in the deflection radial direction of the design orbit. The magnetic field is assumed constant along the design trajectory. Therefore, the designed trajectory is circular, and as the beam energy increases, the trajectory radius and lap time increase.

In such a system, particles slightly deviated from the design trajectory in the radial direction receive a restoring force that returns them to the design trajectory, and at the same time, particles that deviate in the direction perpendicular to the orbital plane are also returned to the orbital plane. receives a restoring force from the main magnetic field. In other words, if the magnetic field is appropriately reduced with respect to the energy of the beam, the particles deviated from the designed trajectory will always have a restoring force acting in the direction of returning them to the designed trajectory, and will vibrate in the vicinity of the designed trajectory. become. This makes it possible to stably circulate and accelerate the beam. Oscillations centered on this design orbit are called betatron oscillations. FIG. 5 shows the value of the magnetic field in the beam of each energy. The magnetic field reaches a maximum of 5 T at the incident portion 130 and decreases to 4.91 T at the outermost circumference.

The main magnetic field distribution described above is excited by magnetizing the magnetic pole 123 by applying a predetermined exciting current to the coil 13 and the trim coil 33 supporting it. In order to form a distribution in which the magnetic field is increased at the ion injection part 130 and decreased toward the outer periphery, the distance (gap) between the magnetic poles 123 facing each other is the smallest at the injection part 130 and increases toward the outer periphery. becomes. Furthermore, the shape of the magnetic pole 123 is symmetrical with respect to a plane (orbital plane) passing through the center of the gap, and has only a magnetic field component in a direction perpendicular to the orbital plane on the orbital plane. Further, fine adjustment of the magnetic field distribution is performed by adjusting the current applied to the trim coils 33 installed on the magnetic pole faces to excite a predetermined magnetic field distribution.

As described above, RF acceleration cavity 21 excites an electric field in acceleration gap 223 . For this purpose, high-frequency power is introduced from an external high-frequency power supply (see low-level high-frequency generator 42 and amplifier 43 in FIG. 10) through input coupler 211, and a high-frequency electric field is generated in acceleration gap 223 between dee electrode 221 and ground electrode 222. Excited.

In general, the electromagnetic field excited by the Dee electrode 221 is an electromagnetic field with a specific resonance frequency and spatial distribution determined by the shape of the electrode. An electromagnetic field with a specific frequency and spatial distribution is called an eigenmode. There are multiple types of eigenmodes, and the mode excited for acceleration is called the fundamental mode. FIG. 6 shows the fundamental mode electromagnetic field distribution and surface current distribution. In FIG. 6, the external shape of the resonator, the distribution of the electric field (E) by the thick arrow, the distribution of the magnetic field (B) by the dotted arrow, and the outline of the current distribution (j) on the surface of the resonator by the solid arrow. . In the fundamental mode, an electric field is generated in the same direction from the dee electrode 221 to the ground electrode 222 everywhere in the gap.

The accelerator 1 modulates the frequency of the electric field corresponding to the energy of the orbiting beam in order to excite a high-frequency electric field in synchronization with the orbiting of the beam. In the high-frequency acceleration cavity 21 using the resonance mode of this embodiment, it is necessary to sweep the high-frequency frequency over a range wider than the resonance width. Therefore, it is necessary to change the resonance frequency of the high-frequency acceleration cavity 21 as well. The control is performed by changing the capacitance of a rotary variable capacitor 212 installed at the end of the high frequency acceleration cavity 21 . The rotary variable capacitor 212 controls the electrostatic capacitance generated between the conductor plate directly connected to the rotary shaft 213 and the external conductor (both not shown) by the rotation angle of the rotary shaft 213 . That is, the rotation angle of the rotating shaft 213 is changed as the beam is accelerated.

The behavior of the beam from the beam injection to the beam extraction of the accelerator 1 will be described. First, low-energy ions are output from the ion source 12 and guided to the beam passing region 20 via the beam-incident through-hole 115 and the incident portion 130 .

The beam incident on the beam passing region 20 is accelerated by the high-frequency electric field, its energy is increased, and the radius of rotation of the trajectory is increased. The beam is then accelerated while ensuring directional stability due to the high-frequency electric field.

The center of gravity of the beam does not pass through the acceleration gap 223 at the time when the high frequency electric field becomes maximum, but passes through the acceleration gap 223 when the high frequency electric field decreases with time. Since the frequency of the high-frequency electric field and the circulating frequency of the beam are synchronized at a ratio of just an integral multiple, the particles accelerated by a given phase of the accelerating electric field are accelerated in the next turn with substantially the same phase. On the other hand, particles accelerated in a phase earlier than the acceleration phase are accelerated in a phase delayed in the next turn because the amount of acceleration is greater than that of particles accelerated in the acceleration phase. Conversely, particles accelerated in a phase later than the acceleration phase when present are accelerated in a phase advanced in the next turn because the amount of acceleration is smaller than that of particles accelerated in the acceleration phase.

In this way, particles whose timing deviates from a predetermined acceleration phase move in the direction of returning to the acceleration phase, and by this action, they can oscillate stably even within the phase plane (advancing direction) consisting of momentum and phase. This oscillation is called synchrotron oscillation. That is, the accelerating particles are gradually accelerated while undergoing synchrotron oscillation and reach a predetermined energy to be taken out. During stable synchrotron oscillation, individual particles rotate on the phase plane within a stable region called a high-frequency bucket.

FIG. 7 shows a schematic diagram of the shape of the high-frequency bucket Bu on the phase plane and the trajectory of particles moving inside it. The width of the high-frequency bucket Bu in both directions of motion is proportional to the square root of the voltage amplitude applied to the acceleration cavity, and the area of the high-frequency bucket Bu is monotonic with respect to the beam energy increase (acceleration speed) per unit time. It is known that each

Under the operating cycle determined by the rotation speed of the rotary variable capacitor 212, the acceleration speed is naturally determined. Therefore, below a certain voltage amplitude, the area of the high-frequency bucket Bu becomes 0, and stable synchrotron oscillation cannot be realized. If the voltage amplitude when the area of the high-frequency bucket Bu exceeds 0 for the first time is called the critical voltage Vc

The critical voltage Vc monotonically increases with beam energy during acceleration. Conversely, when high-frequency power is input to the high-frequency acceleration cavity 21 so as to provide a constant voltage amplitude, the area of the high-frequency bucket Bu gradually decreases as the beam is accelerated. Under the condition that the area of the high-frequency bucket Bu gradually decreases, the momentum dispersion of the beam during acceleration also decreases.

In order to extract a predetermined extraction beam with a target energy, the high frequency electric field applied to the high frequency acceleration cavity 21 is gradually lowered, and when the target energy is reached, the amplitude of the high frequency electric field becomes zero. 40 controls the output from the external high frequency power supply. This allows the beam to circulate stably at the target energy. A high frequency is applied to the disturbance electrode 313 .

The frequency of the high frequency matches the frequency of the beam's betatron oscillations. The beam is disturbed depending on its position in the direction of travel, ie the time of passage through the disturbing electrode 313 . Focusing on a specific particle, since the frequency of the perturbing electric field and the orbiting betatron oscillation are the same, they resonate and the betatron oscillation amplitude of a certain particle increases. When the betatron oscillation amplitude continues to increase, the kick magnetic field excited by the additional magnetic field generating shim 311 installed outside the design orbit causes the betatron oscillation to diverge abruptly. beam is displaced to As a result, the beam is introduced into the extraction septum magnet 312 . The boundary between this stable region and unstable region is called a separatrix.

From the time the target energy is reached until the beam is extracted, the individual particles that make up the beam are positioned in the horizontal direction of the beam by the quadrupolar magnetic field derived from the additional magnetic field generating shim 311 and the multipolar magnetic field of six or more poles. In the phase space determined by the inclination, the orbit is divided into a stable orbital area and an unstable orbital deviation increasing area.

Particles inside the separatrix continue betatron oscillation stably. Particles outside the separatrix undergo a large displacement in the horizontal direction with respect to the design trajectory because the kick action by the additional magnetic field generating shim 311 is accumulated for each revolution. Particles that have undergone a large displacement in the horizontal direction are moved along the extraction orbit 322 by the electric field for disturbance by the disturbance electrode 313 described later and the magnetic field formed by the septum electromagnet 312 for extraction on the extraction orbit 322 set in advance. , and is taken out of the accelerator 1.

When the electric field applied to the perturbation electrode 313 is turned off, the betatron oscillation amplitude of the beam stops increasing and the beam orbits within the stable region. This makes it possible to stop beam extraction.

In the process of extracting the beam, suppressing the momentum dispersion of the circulating beam can suppress the spatial spread of the beam and reduce the amount of the beam lost by colliding with the septum electromagnet 312 or the like. It is valid. Therefore, it is desirable that the area of the high-frequency bucket is made as small as possible at the end of the acceleration to suppress the momentum dispersion of the beam during the orbit.

Moreover, the attenuation of the accelerating electric field takes a certain amount of time based on the Q value of the resonance of the high-frequency accelerating cavity 21 . Typically, the Q value is about 3000, and the high frequency voltage amplitude becomes small and the high frequency bucket disappears in about 3000 cycles from the time when the power input to the high frequency acceleration cavity 21 is stopped. During the attenuation of the high-frequency voltage amplitude, the arrival energy of each particle varies according to the time when the high-frequency bucket collapses as the high-frequency bucket contracts. The more time it takes for the high-frequency bucket to disappear, the more the momentum dispersion of the subsequent orbiting beam spreads in proportion to that time.

From the above, if the high frequency voltage amplitude during acceleration can form a high frequency bucket and if the charge amount of the beam that can be accelerated can be secured sufficiently, the high frequency bucket should be kept as small as possible to improve the extraction efficiency and result. It is effective for shortening the irradiation time.

However, if the high-frequency amplitude voltage is too low, the high-frequency bucket may disappear during acceleration, making it impossible to accelerate the beam to the target energy. For example, there is an optimum RF voltage amplitude value for acceleration up to 70 MeV. However, even if an attempt is made to accelerate to 235 MeV with that high-frequency voltage amplitude value, the high-frequency bucket disappears during acceleration, so acceleration to 235 MeV is not possible.

That is, there is an optimum voltage amplitude in terms of extraction efficiency or irradiation time depending on the target energy to be reached. By exciting the high frequency with the optimum voltage amplitude, it is possible to improve the extraction efficiency or shorten the irradiation time. The accelerator 1 of this embodiment includes the voltage amplitude calculator 45 that holds the correspondence relationship between the arrival energy and the voltage amplitude described above.

So far, the behavior of the beam during one cycle has been described with respect to beam entry and exit. The accelerator 1 repeats similar operations in subsequent cycles. After the second cycle, the already accelerated beam is circulating in the beam passage area 20 with a predetermined energy. In this case, the high-frequency electric field that accelerates the beam in the second cycle also acts on the accelerated beam. However, for the beam that has already been accelerated, the energy of the high frequency that accelerates the beam immediately after incidence does not match the circulating frequency, so the energy only oscillates minutely. Therefore, until the beam in the second cycle approaches the energy of the accelerated beam sufficiently, the accelerated beam stably circulates with almost no change in energy or motion, and part of the beam is extracted. A beam that is already circulating can also be referred to as a leading beam, and a beam that is generated after that as a trailing beam.

When the energy of the second cycle beam (subsequent beam) approaches the energy of the accelerated beam (previous beam), more specifically, the high-frequency bucket containing the second cycle beam in the phase space becomes the accelerated beam does not have a significant effect on the accelerated beam from the radio frequency until it begins to overlap the region where the is present.

FIG. 8 is a schematic diagram of the distribution on the phase space at this timing. A region A1 shaded in gray in FIG. 8 is a region in which the circulating beam that has already been accelerated exists, and the high-frequency bucket Bu containing the beam of the second cycle is included therein.

As described above, the high-frequency bucket is controlled to have an appropriate shape so that the momentum dispersion is small, and its height in the momentum direction is smaller than that of the orbiting beam. When the high frequency bucket and the circulating beam approach each other, the circulating beam cannot enter the high frequency bucket and moves to another position in the phase space so as to be pushed away by the high frequency bucket.

FIG. 9 shows the beam distribution in the phase space at the moment when the second cycle beam acceleration is completed. At the instant shown in FIG. 9, the high frequency bucket passes through a region where the leading beam is already circling, the effect of which is to disturb the distribution of the leading beam and increase the momentum dispersion. Furthermore, the second cycle beam (subsequent beam) spills out of the high-frequency bucket as it contracts, and is arranged in a certain area on the phase space. The region on the phase space between the accelerated beam and the newly accelerated beam has a clear boundary at this timing. In FIG. 9, the area A2 where the accelerated beam (preceding beam) exists is indicated by a dot pattern, and the area A3 where the newly accelerated beam (following beam) exists is indicated by oblique lines. In this way, it is possible to add a new beam at the expense of increasing the momentum dispersion of the circulating beam.

10 and 11, the control diagram and operation flow of each device when the beam is accelerated according to the principle described above and taken out of the accelerator 1 will be described. FIG. 10 shows a control block diagram of the accelerator 1 of this embodiment.

As shown in FIG. 10, the configuration for accelerating the beam and its control system include a rotary variable capacitor 212 attached to the high frequency acceleration cavity 21 and a rotating shaft 213 of the rotary variable capacitor 212 (see FIG. 1). ), and a motor control device 41 that controls the servo motor 214 . Further, there is an input coupler 211 (see FIG. 1) for inputting high frequency power to the high frequency acceleration cavity 21, and a low level high frequency generator 42 and amplifier 43 for generating the high frequency power to be supplied.

The rotary variable capacitor 212 is controlled by the motor controller 41 . The motor control device 41 is controlled by the overall control device 40 . The overall control device 40 controls the motor control device 41 based on the indicated values predetermined by the treatment plan data in the treatment plan database 60 .

When the servomotor 214 rotates at a predetermined rotational speed, this causes the rotating shaft 213 to rotate. The capacitance is temporally modulated by temporally changing the rotation angle of the rotating shaft 213 . This changes the resonant frequency of the fundamental mode.

A high frequency input to the high frequency acceleration cavity 21 is generated by amplifying the high frequency signal generated by the low level high frequency generator 42 with the amplifier 43 . The frequency of the high-frequency signal generated by the low-level high-frequency generator 42 follows the resonance frequency of the fundamental mode. The amplitude of the high-frequency signal is determined by the treatment plan database 60 and instructed by the general control device 40 .

A high-frequency power input to the high-frequency acceleration cavity 21 is generated by amplifying a high-frequency signal generated by a device 42 for generating low-level high-frequency waves for the harmonic mode by an amplifier 43 . The frequency of the high-frequency signal produced by the low-level high-frequency generator 42 for harmonic mode follows the resonance frequency of the harmonic mode, and the amplitude is determined by the energy of the beam determined by the treatment plan database 60. 45 refers to and the amplitude value determined by the calculation of the voltage amplitude calculator 45 is specified by the overall controller 40 .

The configuration and control system for extracting the beam out of the accelerator 1 includes a high-frequency power source 46 for applying a high-frequency voltage to the disturbance electrode 313 and a high-frequency disturbance control device for controlling the high-frequency power source 46, as shown in FIG. 47.

A high-frequency disturbance controller 47 controls the voltage output from the high-frequency power supply 46 to the disturbance electrode 313 . The specified value of the voltage output from the high-frequency power supply 46 is determined by the treatment plan data stored in the treatment plan database 60 as a value uniquely determined from the extraction beam energy and the output current of the extraction beam. The general control device 40 acquires the specified value from the treatment plan data and instructs the disturbance high-frequency control device 47 .

Based on FIG. 11 and FIG. 12, the operation (operating method) of each device in the control system of the accelerator 1 described above when beams of certain two types of energy are continuously extracted will be described. FIG. 11 is a timing chart of the operation of each device. FIG. 12 is a flowchart showing the operation flow.

The vertical axis of the chart in FIG. 11 represents, from the top, (1) the rotation angle of the rotary shaft 213 of the rotary variable capacitor 212, (2) the resonance frequency of the high frequency acceleration cavity 21, and (3) the high frequency acceleration cavity 21. (4) the amplitude of the high frequency for acceleration in the acceleration gap 223; (5) the current waveform of the beam output by the ion source 12; The disturbance high frequency input to the disturbance electrode 313 and (8) the beam current waveform output from the accelerator 1 are shown. The horizontal axis of the chart shown in FIG. 11 is all time.

As shown in FIG. 11, the resonance frequency of the high-frequency acceleration cavity 21 changes periodically depending on the rotation angle of the rotary shaft 213 of the rotary variable capacitor 212 . Correspondingly, the frequency of the high-frequency signal output from the low-level high-frequency generator 42 and input to the high-frequency acceleration cavity 21 also changes synchronously. Here, the period from the time when the resonance frequency reaches its maximum to the next time when it reaches its maximum is defined as the operation period.

As shown in FIG. 11(5), a beam is output from the ion source 12 immediately after the start of the operation cycle. A beam is accelerated if it is injected into a range where stable synchrotron oscillation is possible. On the other hand, particles whose synchrotron oscillation is not stable collide with structures inside the accelerator 1 without being accelerated, and are lost. The process up to this point is the injection process shown in FIG. The injection process includes step S11 of starting application of acceleration voltage and step S12 of outputting ions from the ion source.

Returning to FIG. 11, the beam is accelerated as the resonance frequency decreases, and is accelerated to near the predetermined extraction energy. After that, the amplitude of the high frequency input to the high frequency acceleration cavity 21 begins to decrease. The start timing of this decrease is set to start from a predetermined timing before the ion beam reaches the target energy. For example, it is desirable to start the decrease at the timing when the energy expected to reach the target energy is reached before the acceleration electric field generated in the acceleration gap 223 becomes 0 after the input of the high-frequency power is turned off. This is the acceleration process in FIG. The acceleration process includes step S13 of accelerating the ion beam and step S14 of stopping the application of the acceleration voltage.

Returning to FIG. 11, when the amplitude of the accelerating electric field becomes sufficiently small, the beam has reached the predetermined extraction energy. When the acceleration is completed, the amount of beam that can be extracted reaches a certain value, and beam extraction becomes possible. The beam circulates to fill the separatrix defined by the additional magnetic field generating shim 311 .

Next, a disturbing high frequency is applied by the disturbing electrode 313 . The time for extracting the beam is predetermined. The high-frequency disturbance is applied and the beam continues to be extracted until all the circulating charges are extracted or a predetermined irradiation dose is irradiated.

During this time, the servomotor 214 associated with the high-frequency acceleration cavity 21 continues to rotate, and the resonance frequency continues to fluctuate. When the incident frequency and the resonance frequency match, the beam is output again from the ion source, and while the beam is accelerated in the same manner as described above, the extraction of the beam proceeds in parallel. Only for a very short period of time after the end of acceleration (when the amplitude of the acceleration high frequency is attenuating), the disturbance high frequency is turned off to suppress the energy fluctuation of the irradiation beam. Since the acceleration high frequency generated by the high frequency acceleration cavity 21 does not match the circulating frequency of the beam during the acceleration process, it hardly affects the beam. Therefore, the beam is sequentially extracted by the applied disturbing high frequency wave while circulating with constant energy.

Although it depends on the intensity of the disturbance high frequency, as shown in FIG. 11(6), after the first acceleration is completed, the cyclic charge is always added except for the period during which the amplitude of the acceleration high frequency is attenuating. Therefore, it is possible to control the on/off of the beam at any time. The above is the irradiation process shown in FIG.

The irradiation process includes a step S15 for starting application of the extraction high-frequency wave, a step S16 for stopping the application of the extraction high-frequency wave, a step S17 for determining whether the irradiation process has been completed, a step S18 for measuring the circulating charge amount, and a next cycle. It includes a step S19 of comparing the amount of charge that can be irradiated with a reference value. When it is determined in step S17 that the irradiation process has been completed, the irradiation control process shown in FIG. 12 ends. If the irradiation process has not been completed (S17: NO), the process proceeds to step S18. If it is determined in step S19 that the amount of charge that can be irradiated by the next cycle is greater than the reference value (amount of charge>reference value), the process returns to step S15. If it is determined that the charge amount that can be irradiated by the next cycle is equal to or less than the reference value (charge amount≦reference value), the process returns to step S11.

Return to FIG. When the irradiation with a certain energy ends, the operation is started in a pattern corresponding to the energy of the ion beam to be extracted in the next operation cycle until the next operation cycle is reached. By repeating the above process, the accelerator 1 that can irradiate arbitrary energy with arbitrary dose is realized.

FIG. 11 shows a timing chart in the case of irradiating energy different from the first operation cycle (previous beam operation cycle) in the second operation cycle (subsequent beam operation cycle).

Here, a case will be described in which the irradiation energy of the subsequent beam is greater than the irradiation energy of the preceding beam. As shown in FIG. 11(4), the operation of the trailing beam differs from the operation of the leading beam in the amplitude value of the accelerating high frequency wave and its application period. Acceleration to higher energy is achieved by increasing the application time of the high frequency. As described above, the amplitude value calculated by the voltage amplitude calculator 45 is determined for each energy in order to suppress the momentum dispersion of the circulating beam after acceleration. This avoids making the high-frequency bucket unnecessarily large, and suppresses the momentum dispersion of the circulating beam. Furthermore, it is possible to increase the beam extraction efficiency and shorten the beam irradiation time.

In the above explanation, it is assumed that ions are always injected at a timing when ions can be injected. The amount of charge to be irradiated is compared with the amount of beam actually circulating, and if the amount of circulating charge is sufficiently large, it is conceivable not to inject new ions (ion output from the ion source 12). In that case, the accelerator 1 is provided with an electrode-type orbiting beam intensity monitor BM (see FIG. 2) as means for monitoring the beam intensity. The beam amount monitor BM is an electrode installed at an arbitrary position on the beam trajectory, and can extract a signal proportional to the voltage and charge amount excited on the electrode. If the amount of charge circulating is greater than the predetermined amount of charge, the injection of ions is skipped.

Other methods may be used for the beam amount monitoring means. There is no need to measure the beam amount directly. Since the ratio of the amount of extracted beam to the high-frequency amplitude for disturbance is an amount related to the amount of circulating beam, a method of estimating the amount of beam from the ratio may be used.

For example, it is also possible to measure the beam circulation amount by using a loop antenna for acquiring a pick-up signal of the accelerating cavity, or a reflected wave monitor from the input coupler. In this case, calibration is performed in advance in consideration of the circulating frequency of the beam and the bunch structure of the beam, and a calibration table based on the energy of the beam and the elapsed time from acceleration stop is prepared.

FIG. 13 shows a flowchart of processing for measuring the beam amount. The beam amount measurement process includes, for example, a step S20 of acquiring a pick-up signal of the acceleration electrode, a step S21 of analyzing the frequency of the acquired signal, a step S22 of acquiring the signal intensity corresponding to the beam frequency, and frequency characteristics and acceleration stop. A step S23 is included in which the amount of beam is converted with the elapsed time from .

That is, in the beam amount measurement process, after the measurement is started (S20), the signal of the specific frequency component of the monitor signal is taken out (S21, S22) and converted into the circulating beam amount from the calibration table (S23). Accordingly, it is possible to determine whether or not to skip the injection of new ions based on the circulating charge amount.

The high frequency acceleration cavity 21 is not limited to the configuration described above. For example, as a modulating mechanism for the high-frequency cavity, instead of changing the electrostatic capacity of the rotary variable capacitor 212, the change in magnetic permeability can be used. By placing a ferrite magnetic material inside the cavity, it is possible to utilize the change in magnetic permeability caused by an external magnetic field, which is the property of the ferrite magnetic material.

FIG. 14 shows the structure of the high frequency acceleration cavity 21 in that case. FIG. 14 shows a resonance cavity in which one end of the acceleration cavity has a coaxial structure, and a ferrite magnetic body 231 is placed in the gap surrounded by the inner body and the outer conductor in the coaxial structure. A bias current coil 232 is wound around the ferrite magnetic body 231 and connected to an external power source. The current applied to the bias current coil 232 depends on the radio frequency. Since the magnetic permeability of the ferrite magnetic body 231 is determined by the value of the bias current, it is possible to form a table of the relationship between the resonance frequency and the bias current in advance. Therefore, when using this type of acceleration cavity, unlike modulation using a variable capacitor, the high frequency is controlled by controlling the bias current.

According to this embodiment configured in this way, it is possible to execute in parallel time-sequential processes of the ion injection process, the ion acceleration process, the ion beam extraction process, and the deceleration process. The accelerator 1 of this embodiment repeatedly executes the injection process and the acceleration process, and maintains a state in which the beam corresponding to the irradiation energy is constantly replenished within the accelerator. Therefore, the accelerator 1 of this embodiment can shorten the time during which the beam cannot be irradiated and improve the efficiency of beam extraction.

Example 2 will be described. In the following examples including this example, differences from the first example will be mainly described. Embodiment 2 is not shown, but can be understood and implemented by those skilled in the art.

In Example 1, hydrogen ions were used as accelerating nuclides, but in Example 2, carbon ions were used as accelerating nuclides. The accelerator of Example 2 is a frequency-modulated variable energy accelerator capable of extracting carbon ions with a kinetic energy per nucleon in the range of 140 MeV to 430 MeV.

Since the principle of operation of the accelerator of Example 2, its equipment configuration, and its operating procedure are the same as those described in Example 1, detailed description thereof will be omitted.

The accelerator of the second embodiment differs from the accelerator 1 of the first embodiment in the relationship between the size of the orbital radius, the magnetic field and energy, and the relationship between the orbital frequency and energy. They can be determined from the accelerator 1 shown in Example 1 by making the product of the orbital radius and the magnetic field proportional to the ratio of the magnetic stiffness of the beam.

Therefore, also in the accelerator of the second embodiment, the same configuration and method as those of the accelerator 1 of the first embodiment produce the same effects as those of the first embodiment. That is, the accelerator of Example 2 can suppress the momentum dispersion of the orbiting beam, can improve the extraction efficiency and shorten the irradiation time when used for particle beam therapy, compared to the operation method of the conventional technology.

Example 3 will be described with reference to FIG. A third embodiment describes a particle beam therapy system 1000 including the accelerator 1 described in the first embodiment or the accelerator described in the second embodiment. FIG. 15 is an overall configuration diagram of a particle beam therapy system.

As shown in FIG. 15, the particle beam therapy system 1000 sets the energy of proton beams or carbon beams (hereinafter collectively referred to as beams) to an appropriate value depending on the depth from the body surface of the affected area, and treats the patient. It is an irradiation device.

A particle beam therapy system 1000 includes an accelerator 1 , a beam transport system 2 , an irradiation device 3 , a treatment table 4 , a general control device 40 , an irradiation control device 50 , a treatment plan database 60 and a treatment planning device 70 .

Accelerator 1 was described in Example 1 or Example 2. The beam transport system 2 is a mechanism that transports the beam accelerated by the accelerator 1 to the irradiation device 3 . The irradiation device 3 is a device that irradiates a target in the patient 5 fixed on the treatment table 4 with the beam transported by the beam transport system 2 . A general controller 40 controls the accelerator 1 , the beam transport system 2 and the irradiation device 3 . The irradiation controller 50 controls beam irradiation to the target. The treatment plan database 60 stores treatment plans created by the treatment planning device 70 . The treatment planning device 70 creates a beam irradiation plan for the target.

In the particle beam therapy system 1000, the energy and dose of the irradiated particle beam are determined by the treatment plan. The energy and dose of the particle beam determined by the treatment plan are sequentially input from the overall control device 40 to the irradiation control device 50 . As a result, the particle beam therapy system 1000 performs a procedure of transferring to the next energy when an appropriate dose is applied, and irradiating the particle beam again.

According to the particle beam therapy system 1000 of the third embodiment configured in this manner, it is possible to utilize the characteristic of the accelerator 1 of the first embodiment or the accelerator of the second embodiment that irradiation can be completed in a short time. , can provide a system with a short irradiation time.

The beam transport system 2 of the particle beam therapy system 1000 can also use a rotating gantry instead of a fixed irradiation device. The rotating gantry can rotate around the patient 5 together with the irradiation device 3 to irradiate the beam. Furthermore, a plurality of fixed irradiation devices 3 may be provided. Furthermore, the beam may be directly transported from the accelerator 1 to the irradiation device 3 without providing the beam transport system 2 .

In addition, this invention is not limited to embodiment mentioned above. Those skilled in the art can make various additions, modifications, etc. within the scope of the present invention. The above-described embodiments are not limited to the configuration examples illustrated in the attached drawings. The configuration and processing method of the embodiment can be changed as appropriate within the scope of achieving the object of the present invention.

In addition, each component of the present invention can be selected arbitrarily, and the present invention includes an invention having a selected configuration. Furthermore, the configurations described in the claims can be combined in addition to the combinations specified in the claims.

Reference Signs List 1 Accelerator 2 Beam transport system 3 Irradiation device 11 Electromagnet 12 Ion source 13 Coil 20 Beam passage area 21 High frequency acceleration cavity 33 Trim coil 40 Overall control device 41 Motor control device 42 Low Level high-frequency generator 43 Amplifier 45 Voltage amplitude calculator 46 High-frequency power supply 47 High-frequency disturbance control device 50 Irradiation control device 60 Treatment plan database 70 Treatment planning device 111 Extraction beam through-holes 112, 113 Coil Through-hole for connection 114 High-frequency power input through-hole 115 Beam incident through-hole 121 Return yoke 122 Top plate 123 Magnetic pole 130 Incidence part 211 Input coupler 212 Rotary variable capacitor 213 Rotary shaft 214 Servo motor 221 Dee electrode 222 Ground electrode 223 Acceleration gap 231 Ferrite magnetic material 232 Bias current coil 311 Additional magnetic field generating shim 312 Extraction septum electromagnet 313 Disturbance abuse electrode 322 Extraction trajectory 1000 Particles Radiation therapy system

Claims (5)

An orbital accelerator that accelerates ions supplied from an ion source to generate a beam with a main magnetic field and a frequency-modulated high-frequency electric field,
an accelerating high-frequency applying device capable of frequency modulation and applying an accelerating high-frequency wave for accelerating ions;
an extracting high-frequency applying device for applying an extracting high-frequency wave for extracting the beam, the extracting high-frequency applying device having a frequency different from the accelerating high-frequency wave;
a disturbance magnetic field region forming part for forming a disturbance magnetic field region;
a septum magnet for beam extraction;
An accelerator into which new ions are supplied from the ion source and accelerated during extraction of the beam. An orbital accelerator that accelerates ions supplied from an ion source to generate a beam with a main magnetic field and a frequency-modulated high-frequency electric field,
an accelerating high-frequency applying device capable of frequency modulation and applying an accelerating high-frequency wave for accelerating ions;
an extracting high-frequency applying device for applying an extracting high-frequency wave for extracting the beam, the extracting high-frequency applying device having a frequency different from the accelerating high-frequency wave;
a disturbed magnetic field region forming unit for forming a disturbed magnetic field region composed of a high-order magnetic field including magnetic field components with a plurality of poles and including at least four pole magnetic field components;
a septum magnet for beam extraction;
An accelerator in which ions supplied from the ion source in one cycle are accelerated until they have approximately the same energy as ions supplied in another cycle prior to the said cycle and already orbiting. An accelerator for accelerating ions to produce a beam,
a pair of magnets arranged facing each other, the pair of magnets having magnetic poles for forming a magnetic field therebetween;
an ion source that outputs ions between the pair of magnets;
an accelerating electrode that forms an accelerating electric field that accelerates the ions;
a modulation unit for modulating the frequency of the accelerating electric field;
a kick portion disposed between the magnetic poles of the pair of magnets and providing a kick action from the stable region to the ions orbiting by the magnetic field formed by the magnetic poles;
a disturbance unit that generates a disturbance electric field that disturbances the ions in the radial direction;
a high-frequency electric field control unit that controls the electric field for acceleration;
high-frequency electric field amplitude determination means for inputting the amplitude value of the acceleration electric field to the high-frequency electric field control unit;
a disturbance intensity control unit that controls the electric field for disturbance;
with
Circular trajectories of a plurality of annular ions formed by the pair of magnets, in which ions of different energies respectively circulate, have an area where orbits are concentrated and an area where the orbits are discrete,
The modulating unit periodically modulates the electric field frequency according to a period,
The high-frequency electric field amplitude determining means determines the voltage amplitude according to the energy of the irradiated beam,
The ion source outputs ions during a period in which the frequency of the accelerating electric field is a specific value,
the value of the frequency at which the ions are output is deviated from the orbital frequency corresponding to the energy of the extracted beam;
An accelerator in which ions output from the ion source are ions output in another cycle and are accelerated until they have approximately the same energy as ions already in a circulating state. Furthermore, a beam amount monitoring means is provided,
2. The accelerator according to claim 1, wherein whether or not to output said ions is determined based on the circulating beam amount obtained by said beam amount monitoring means. an irradiation device for irradiating a target with ions accelerated by the accelerator according to any one of claims 1 to 4;
a control device that controls the accelerator and the irradiation device;
A particle beam therapy system with

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