Charged particle emission control device, method and computer program product

Abstract

The present invention provides a charged particle emission control technology, which can stably perform slow extraction of a charged particle beam from a synchrotron even when beam adjustment is not implemented or completed. The charged particle emission control device (10) comprises: a first receiving unit (11) for receiving a first detection signal (S1) obtained by detecting the current value of a charged particle swirling in a synchrotron (20); a processing unit (16) for performing time differentiation on the first detection signal (S1) and outputting a beam intensity equivalent value (D); and an emission control unit (18) for outputting a control signal (G) for causing a charged particle beam (51) to be emitted from a synchrotron (20) to a beam transport system (30) in a manner that the beam intensity equivalent value (D) is consistent with a target value (17).

Description

Technical Field

[0001] Embodiments of the present invention relate to a technique for controlling the emission of charged particles whirling in a synchrotron. Background Art

[0002] In recent years, research on the application of charged particles (ions) supplied to accelerators to accelerate them into charged particle beams in a high-energy state has been promoted in a wide range of fields such as engineering and medicine. The accelerator system currently in widespread use is roughly composed of an ion source, a linear accelerator (linac), and a circular accelerator (synchrotron), and the charged particles are accelerated in this order. In addition, when the charged particles whirled in the synchrotron reach a specified energy, the emission control device is activated to extract the charged particle beam whose travel direction has been changed from the whirling orbit to the beam transport system.

[0003] The emission control device for extracting charged particle beams from synchrotrons is classified into fast extraction and slow extraction according to specifications. "Fast extraction" refers to a method of extracting all the groups (beams) of charged particles whirling around the synchrotron within the time required for one revolution.

[0004] In contrast, "slow extraction" refers to a method of extracting a charged particle beam little by little while spinning in a synchrotron. Therefore, a charged particle beam irradiated by "slow extraction" can be extracted little by little after spinning many times compared to "fast extraction".

[0005] In the case where a particle beam therapy device scans and irradiates a lesion with a charged particle beam, it is necessary to extract the charged particle beam from the synchrotron in a manner that reduces the variation of the beam intensity. In addition, in order to monitor the supply of a charged particle beam with a stable intensity to the beam delivery system, a beam intensity monitor is provided at at least one of the irradiation port of the treatment room or the beam delivery system to detect the beam intensity of the charged particles. In addition, the detected value is fed back to the emission control device to appropriately control the beam intensity of the charged particles extracted from the synchrotron in a manner that the detected value becomes a preset value.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2017-112021 Summary of the invention

[0009] However, when installing an accelerator system and a particle beam therapy device on site or performing system maintenance, various equipment adjustment operations are performed. This adjustment operation is sometimes performed while slowly extracting a charged particle beam from a synchrotron. However, sometimes when the adjustment of the beam delivery system is not completed, the charged particle beam cannot be made to reach the irradiation port or the monitor of the beam delivery system arranged in the treatment room. In this case, in the above-mentioned known technology, feedback control cannot function, so the slow extraction of the charged particle beam cannot be stably performed from the synchrotron.

[0010] However, one of the adjustments of the beam delivery system is a beam adjustment operation that gradually adjusts the current value of the electromagnet so that the charged particle beam passes through the center of the tube and the beam size reaches a target value. Therefore, if the slow extraction of the charged particle beam that controls the beam intensity to a certain value cannot be performed stably, the adjustment operation is extremely difficult and takes a long time.

[0011] The embodiments of the present invention have been proposed in consideration of these circumstances, and an object of the present invention is to provide a charged particle emission control technology that can stably extract a charged particle beam slowly from a synchrotron even when beam adjustment is not performed or completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a block diagram of a charged particle emission control device according to the first embodiment of the present invention.

[0013] Figure 2 (A), (B), (C), (D), and (E) are timing diagrams for explaining the emission control of charged particles according to the embodiment.

[0014] Figure 3 This is a block diagram of a charged particle emission control device according to the second embodiment.

[0015] Figure 4 This is a flowchart for explaining the charged particle emission control method and emission control program according to the first embodiment.

[0016] Figure 5 It is a flowchart explaining the emission control method and emission control program of charged particles according to the second embodiment. DETAILED DESCRIPTION

[0017] (First Embodiment)

[0018] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1This is a block diagram of a charged particle emission control device 10A (hereinafter referred to as "emission control device 10A") according to a first embodiment of the present invention. Such an emission control device 10A (10) comprises: a first receiving unit 11 for receiving a first detection signal S1 obtained by detecting the current value of a charged particle swirling in a synchrotron 20; a calculation processing unit 16 for performing a calculation including at least time differentiation on the first detection signal S1 and outputting a beam intensity equivalent value D; and an emission control unit 18 for outputting a control signal G for causing a charged particle beam 51 to be emitted from the synchrotron 20 to a beam transport system 30 in such a manner that the beam intensity equivalent value D is consistent with a target value 17a.

[0019] Furthermore, the injection control device 10A (10) includes a noise filter 15 for removing noise components contained in the first detection signal S1 before the first detection signal S1 is time-differentiated by the operation processing unit 16. Furthermore, an amplifier (not shown) is provided for amplifying the first detection signal S1 as an analog signal before inputting the first detection signal S1 into the noise filter 15. The amplified first detection signal S1 may be directly processed as an analog signal in the noise filter 15 and the operation processing unit 16, or may be converted into a digital signal and then processed in the noise filter 15 and the operation processing unit 16.

[0020] In this way, by removing the noise component from the first detection signal S1, the accuracy of the differential processing of the calculation processing unit 16 is improved, and as described later, the matching of the beam intensity of the charged particle beam 51 and the beam intensity equivalent value D is improved. In addition, the calculation processing unit 16 can set the time differential value of the first detection signal S1 to the beam intensity equivalent value D, or further multiply the time differential value of the first detection signal S1 by a conversion coefficient and set it to the beam intensity equivalent value D.

[0021] The accelerator system is composed of an ion source 21, a linear accelerator 22, and a synchrotron 20, and the charged particles are accelerated in stages in this order. After the charged particles whirled in the synchrotron 20 reach a predetermined energy, the ejection device 29 is operated while maintaining the energy, and the charged particle beam 51 whose traveling direction has been changed from the whirling orbit is drawn out to the beam transport system 30. In addition, in this description, "energy" refers to "energy occupied by nucleons".

[0022] The ion source 21 may be a high frequency (including microwave) irradiation type ion source such as an ECR (Electron Cyclotron Resonance) ion source or a PIG (Penning Ionization Gauge) ion source, or a laser irradiation type ion source, but is not limited thereto.

[0023] The linear accelerator 22 arranges a plurality of accelerating electric fields adjacent to each other and having electric field components in opposite directions in a straight line, and repeatedly reverses the direction of the electric field at a high frequency, so that the charged particles passing through the accelerating electric field are always accelerated in only one direction. Furthermore, the linear accelerator 22 accelerates the ions incident from the ion source 21 to a predetermined energy and then emits them to the synchrotron 20.

[0024] The synchrotron 20 is composed of a high-frequency acceleration cavity 25, a plurality of deflection electromagnets 26, a plurality of quadrupole electromagnets 27, a current detector 28, and an ejection device 29. The high-frequency acceleration cavity 25 accelerates the charged particles incident from the linear accelerator 22 through high-frequency power; the plurality of deflection electromagnets 26 generate a magnetic field that imparts centripetal force to the swirling charged particles; the plurality of quadrupole electromagnets 27 generate a magnetic field that causes the swirling charged particles to diverge / converge and control them within a swirling orbit; the current detector 28 detects the current value of the beam of the swirling charged particles; and the ejection device 29 ejects the beam of charged particles swirling around the synchrotron 20 little by little to the beam transport system 30.

[0025] The synchrotron 20 configured in this way can spin the beam of charged particles incident from the linear accelerator 22 at low energy and finally accelerate it to an upper limit energy of 70 to 80% of the speed of light. Furthermore, the synchrotron 20 can maintain the energy of the beam of charged particles being swirled at an arbitrary energy lower than the upper limit energy. Furthermore, the accelerator control unit 23 controls the ion source 21, the linear accelerator 22, and the synchrotron 20 in a linked manner so that the acceleration of the beam of charged particles described above is performed correctly.

[0026] In addition, the beam delivery system 30 is also provided with a quadrupole electromagnet 27 for controlling the charged particles traveling in a straight line within the track, and a deflection electromagnet 26 for applying centripetal force to the charged particles to bend the track. Furthermore, an irradiation device 50 for treating a patient's tumor by irradiating a charged particle beam 51 is connected after the beam delivery system 30. In addition, the irradiation device 50 is an example, and the facilities connected after the beam delivery system 30 are not particularly limited.

[0027] The ejection device 29 used in the embodiment is a "slow extraction" specification that gradually extracts a group (beam) of charged particles swirling in the synchrotron 20. The ejection device 29 excites an ejection electrode (not shown) based on a control signal G input from the ejection control device 10, thereby extracting the beam that has migrated to the unstable region from the synchrotron 20 to the beam transport system 30.

[0028] In addition, a beam intensity monitor 55 a is provided in the beam transport system 30 , and a beam intensity monitor 55 b is provided in the irradiation device 50 , so that the beam intensity of the charged particle beam 51 can be monitored.

[0029] Figure 2 FIG. 1 is a timing chart for explaining the emission control of charged particles according to the embodiment. Figure 2 The timing shown in (A) is from the accelerator control unit 23 ( Figure 1 ) sends a command signal 61 to the ion source 21. Then, the charged particles are output from the ion source 21, and after being accelerated by the linear accelerator 22, the beam of the charged particles is supplied to the synchrotron 20.

[0030] Figure 2 (B) indicates that the accelerator control unit 23 ( Figure 1 ) is a profile of the excitation current applied to the deflection electromagnet 26. The excitation current applied to the deflection electromagnet 26 is a value uniquely determined according to the energy of the swirling charged particles, so it can also be understood as Figure 2 (B) is a schematic graph showing the energy of charged particles whirling in the synchrotron 20 .

[0031] Before sending the command signal 61, the synchrotron 20 is set to an initial state corresponding to cyclotron the charged particles having incident energy E0 just after being supplied from the linear accelerator 22. Then, from the time of incident beam of charged particles, the synchrotron 20 changes the set state to a direction in which the energy of the charged particles increases, and maintains the set state after stabilizing to a predetermined energy E1.

[0032] Figure 2 (C) indicates that when the linear accelerator 22 is set to maintain the energy E1 (or E2, E3), the ejection control device 10 ( Figure 1 ) during the period T of sending the control signal G to the injection device 29. Thus, during the period T of sending the control signal G to the injection device 29, the beam of charged particles swirling in the synchrotron 20 is gradually drawn out to the beam transport system 30.

[0033] Figure 2 (D) indicates that the current detector 28 ( Figure 1 ) is a schematic curve of a first detection signal S1 obtained by detecting the current value of a beam of charged particles whirling in the synchrotron 20. Figure 2 (E) indicates that in the operation processing unit 16 ( Figure 1 ) is a rough curve of the beam intensity equivalent value D obtained by time-differentiating the first detection signal S1.

[0034] In addition, the number of charged particles passing through the beam delivery system 30 is consistent with the number of charged particles circling around the synchrotron 20 when beam adjustment is properly performed without loss. Therefore, the beam intensity equivalent value D corresponds to the beam intensity of the charged particle beam 51 drawn out to the beam delivery system 30. Therefore, by implementing the feedback of the beam intensity equivalent value D of the first detection signal S1 from the synchrotron 20 to make it consistent with the target value 17a ( Figure 1 ) can generate a control signal G for the charged particle beam 51 that stabilizes the beam intensity in the emission control unit 18. In this way, the beam of charged particles can be gradually drawn from the synchrotron 20 to the beam transport system 30. Furthermore, the energy setting state of the synchrotron 20 can be changed in stages, such as E1, E2, and E3.

[0035] As the time T during which the control signal G is sent to the ejection device 29 passes, the beam of charged particles whirling in the synchrotron 20 decreases or disappears. Therefore, the setting state of the synchrotron 20 is returned (decelerated) from the energy E1, E2, E3 to the state of the initially set incident energy E0, and the command signal 61 is sent to the ion source 21 again to supply the beam of charged particles to the synchrotron 20 again. In addition, the reduced old beam of charged particles deviates from the whirling orbit in this deceleration process and completely disappears.

[0036] In addition, the setting state of the synchrotron 20 can be maintained at an arbitrary level lower than the upper limit energy. Therefore, the beam of charged particles that are resupplied can be stabilized and maintained at different energies E1, E2, and E3. In this way, a series of processes are repeated: the beam of charged particles is supplied to the synchrotron 20 for acceleration, the charged particle beam 51 is emitted to the beam transport system 30, the beam of charged particles is decelerated, and the beam of charged particles is supplied to the synchrotron 20 again.

[0037] (Second Embodiment)

[0038] Figure 3 1 is a block diagram of a charged particle emission control device 10B (hereinafter referred to as "emission control device 10B") according to the second embodiment. Figure 3 With Figure 1 Components having the same structure or function are denoted by the same reference numerals, and repeated descriptions are omitted.

[0039] The emission control device 10B (10) of the second embodiment further includes, in addition to the structure of the emission control device 10A, a second receiving unit 12 for receiving a second detection signal S2 obtained by detecting the intensity of the charged particle beam 51 emitted to the beam transport system 30, and a switching unit 19 for switching and outputting either the input beam intensity equivalent value D or the second detection signal S2, and an emission control unit 18 for outputting a control signal G for causing the charged particles to be emitted from the synchrotron 20 to the beam transport system 30 in such a manner that the second detection signal S2 coincides with the target value 17b. Here, the switching unit 19 can also switch whether to receive the output of the beam intensity monitor 55a or the output of the beam intensity monitor 55b with respect to the second detection signal S2.

[0040] At this time, the emission control device 10B switches the feedback coefficient 14 required for outputting the control signal G along with the switching of the beam intensity equivalent value D and the second detection signal S2. The intensity of the charged particle beam 51 emitted to the beam transport system 30 can be detected by the beam intensity monitors 55a and 55b.

[0041] In the first embodiment, a control signal G is generated and sent to the emission device 29 based on the beam intensity equivalent value D of the first detection signal S1 of the current value of the beam of charged particles whirling in the synchrotron 20. It can be considered that the emission control of the charged particle beam 51 of the first embodiment is sufficient for the adjustment work of various devices constituting the beam delivery system 30. However, the charged particle beam 51 irradiated to the patient 52 still has instability in accuracy.

[0042] Therefore, when treating the patient 52, the switching unit 19 switches the feedback target from the beam intensity equivalent value D of the first detection signal S1 of the beam current value to the second detection signal S2 of the intensity of the charged particle beam 51. This can further stabilize the control of the charged particle beam 51 actually irradiating the patient 52.

[0043] Figure 4 is a flowchart for explaining the ejection control method and ejection control program of the charged particles according to the first embodiment (refer to Figure 1 , Figure 2 ). First, in the adjustment phase of the equipment constituting the beam transport system 30 (S10), the synchrotron 20 is set to an initial state (S11). Then, a command signal 61 is sent to the ion source 21 to cause it to output charged particles (S12).

[0044] Then, the beam of charged particles is accelerated by the linear accelerator 22 and supplied to the synchrotron 20. Furthermore, the beam of charged particles is accelerated by the synchrotron 20 and stabilized to a predetermined energy E1 (S13: No, Yes).

[0045] Then, the first detection signal S1 obtained by detecting the current value of the beam of charged particles whirling in the synchrotron 20 at the current detector 28 is received (S14), and the beam intensity equivalent value D obtained by time-differentiating the first detection signal S1 is output (S15).

[0046] Then, the control signal G generated by feeding back the beam intensity equivalent value D in a manner consistent with the target value 17a is output to the emission device 29 (S16), so that the charged particle beam 51 is emitted from the synchrotron 20 to the beam transport system 30 (S17). During the period when the charged particle beam 51 is emitted to the beam transport system 30, beam adjustment is performed (S18: Yes). In addition, sometimes the energy setting state of the synchrotron 20 is changed in stages such as E1, E2, and E3 to perform beam adjustment.

[0047] Then, when the beam of charged particles whirling in the synchrotron 20 is reduced and the first detection signal S1 output by the current detector 28 reaches the lower limit value (S19: No, Yes), the synchrotron 20 is returned to the initial state, and the process of (S11) to (S19) is repeated. Then, after the beam adjustment is completed (S18: No), the process ends (END).

[0048] Figure 5 is a flowchart for explaining the emission control method and emission control program of the charged particles according to the second embodiment (refer to Figure 1 , Figure 2 In the second embodiment, in addition to the process of (S11) to (S19) of the first embodiment, a switching unit 19 ( Figure 3 ) operation to change the feedback object from the first detection signal S1 to the second detection signal S2 (S20: No, Yes), and the processes of (S21) to (S25).

[0049] After the object of feedback is changed to the second detection signal S2 (S20: Yes), the intensity of the charged particle beam 51 detected by the beam intensity monitor 55a (or 55b) is received as the second detection signal S2 (S21) while the charged particle beam 51 is being emitted to the beam transport system 30. Furthermore, the control signal G generated by feeding back the second detection signal S2 in a manner consistent with the target value 17b is output to the emission device 29 (S22), so that the charged particle beam 51 is emitted from the synchrotron 20 to the beam transport system 30 (S23). During the period when the charged particle beam 51 is emitted to the beam transport system 30 in this way, beam adjustment is performed (S24: Yes).

[0050] Then, when the beam of charged particles whirling in the synchrotron 20 is reduced and the first detection signal S1 output by the current detector 28 reaches the lower limit value (S25: No, Yes), the synchrotron 20 is returned to the initial state, (S11) to (S13) are skipped, and the process of (S21) to (S25) is repeated. Then, after the beam adjustment is completed (S24: No), the process ends (END).

[0051] According to at least one embodiment of the charged particle emission control device described above, by feeding back the differential value of the current value of the charged particles circling in the synchrotron, the charged particle beam can be stably and slowly extracted from the synchrotron even when beam adjustment is not implemented or completed.

[0052] Several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the main purpose of the invention. These embodiments and their variations are included in the scope or main purpose of the invention, and are included in the invention described in the claims and their equivalents. In addition, the constituent elements of the charged particle emission control device can also be implemented by a computer processor, and can be operated according to the charged particle emission control program.

[0053] The charged particle emission control device described above can be realized by utilizing the hardware structure of a conventional computer, which hardware structure has: a control device, a highly integrated dedicated chip, a processor such as an FPGA (Field Programmable Gate Array), a GPU (Graphics Processing Unit), or a CPU (Central Processing Unit); a storage device such as a ROM (Read Only Memory) or a RAM (Random Access Memory); an external storage device such as a HDD (Hard Disk Drive) or a SSD (Solid State Drive); a display device such as a monitor; an input device such as a mouse and a keyboard; and a communication I / F.

[0054] Furthermore, the program executed in the charged particle emission control device is provided by being pre-loaded into a ROM, etc. Alternatively, the program can also be provided in a computer-readable storage medium such as a CD-ROM, CD-R, memory card, DVD, or floppy disk (FD) in the form of an installable or executable file.

[0055] Furthermore, the program executed in the charged particle emission control device of this embodiment can also be stored in a computer connected to a network such as the Internet, and provided by downloading via the network. Furthermore, the device can also be composed of separate modules that independently perform the functions of the constituent elements and are connected and combined through a network or a dedicated line.

Claims

1. A charged particle emission control device, comprising: a first receiving unit that receives a first detection signal obtained by detecting a current value of a charged particle circling in a synchrotron; a calculation processing unit that performs a calculation including at least time differentiation on the first detection signal and outputs a beam intensity equivalent value; an emission control unit that, when the beam intensity equivalent value is input, outputs a control signal for causing a charged particle beam to be emitted from the synchrotron to a beam transport system in a manner that the beam intensity equivalent value is consistent with a target value; a second receiving unit that receives a second detection signal obtained by detecting the intensity of the charged particle beam emitted to the beam transport system; and a switching unit that switches which of the beam intensity equivalent value and the second detection signal is input to the emission control unit, and when the second detection signal is input, the emission control unit outputs a control signal for causing the charged particle to be emitted from the synchrotron to the beam transport system in a manner that the second detection signal is consistent with the target value.

2. The charged particle emission control device according to claim 1, wherein: The injection control device includes a noise filter for removing a noise component included in the first detection signal before performing the time differentiation.

3. The charged particle emission control device according to claim 1, wherein: As the beam intensity equivalent value and the second detection signal are switched, the feedback coefficient required for outputting the control signal is also switched.

4. A method for controlling the emission of charged particles, comprising the following steps: Receive a first detection signal obtained by detecting the current value of a charged particle swirling in a synchrotron; perform an operation including at least time differentiation on the first detection signal and output a beam intensity equivalent value; when the beam intensity equivalent value is input, output a control signal for causing the charged particle beam to be emitted from the synchrotron to a beam transport system in a manner that the beam intensity equivalent value is consistent with a target value; receive a second detection signal obtained by detecting the intensity of the charged particle beam emitted to the beam transport system; and switch the beam intensity equivalent value to the second detection signal, and output a control signal for causing the charged particles to be emitted from the synchrotron to the beam transport system in a manner that the second detection signal is consistent with the target value.

5. A computer program product, comprising a charged particle emission control program, wherein the emission control program causes a computer to execute the following steps: receiving a first detection signal obtained by detecting a current value of a charged particle swirling in a synchrotron; performing an operation including at least time differentiation on the first detection signal and outputting a beam intensity equivalent value; when the beam intensity equivalent value is input, outputting a control signal for causing a charged particle beam to be emitted from the synchrotron to a beam transport system in a manner such that the beam intensity equivalent value is consistent with a target value; receiving a second detection signal obtained by detecting the intensity of the charged particle beam emitted to the beam transport system; and switching the beam intensity equivalent value to the second detection signal, and outputting a control signal for causing the charged particles to be emitted from the synchrotron to the beam transport system in a manner such that the second detection signal is consistent with the target value.

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