Scanning electromagnet control system, scanning electromagnet control method, and particle beam therapy system

Abstract

To provide a scanning electromagnet control system capable of scanning charged particle beams at higher speed.SOLUTION: A scanning electromagnet 1 applies a magnetic field generated by coils U, V, and W of a plurality of systems whose end edges are connected to each other, to charged particle beams so as to deflect charged particle beams. When fixing the direction of the charged particle beams, a scanning electromagnet control system 2 applies a constant voltage according to the direction to each starting end of the coils U, V, and W of the scanning electromagnet 1. When changing the direction of the charged particle beams, the scanning electromagnet control system applies a variation voltage in which a potential difference between the starting ends is greater than a potential difference before and after the change in the direction, to each starting end of the coils U, V, and W.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a scanning electromagnet control system, a scanning electromagnet control method, and a particle beam therapy system.

Background Art

[0002] Particle beam therapy, which irradiates a diseased part with a charged particle beam (charged particle ray) such as a proton beam or a carbon ion beam, has become widespread. In a particle beam therapy system that performs particle beam therapy, a charged particle beam accelerated to have the necessary energy by an accelerator is transported to an irradiation nozzle by a transport device and irradiated from the irradiation nozzle to the diseased part.

[0003] In particle beam therapy, scanning irradiation may be performed in which the diseased part is irradiated while changing the irradiation position of the charged particle beam. In scanning irradiation, the depth of the irradiation position of the charged particle beam is changed by changing the energy of the charged particle beam. Further, by generating a magnetic field in a direction crossing the charged particle beam and deflecting the charged particle beam, the irradiation position in a plane substantially perpendicular to the depth direction is changed. For this reason, the accelerator is provided with a device for controlling the energy of the charged particle beam, and the irradiation nozzle is provided with a scanning electromagnet that generates a magnetic field in a direction crossing the charged particle beam.

[0004] Patent Document 1 discloses a scanning electromagnet capable of two-dimensionally scanning a charged particle beam. This scanning electromagnet generates a magnetic field corresponding to the irradiation position by applying a desired excitation current to each of three terminals connected to three systems of windings. Further, in this scanning electromagnet, when changing the irradiation position, the excitation current is changed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] Patent Document 1 discloses excitation currents corresponding to irradiation positions, but does not disclose a method for setting the voltage applied to each terminal when changing the irradiation position. When changing the irradiation position, the excitation current changes, generating a back electromotive force due to the inductance of the coil. Therefore, if an appropriate voltage is not applied, the back electromotive force may reduce the scanning speed or prevent the scanning path from following the desired trajectory, potentially increasing the time required to change the irradiation position. A longer time required to change the irradiation position results in a longer irradiation time for the charged particle beam, which in turn affects the patient's burden and the throughput of treatment.

[0007] The object of the present invention is to provide a scanning electromagnet control system, a scanning electromagnet control method, and a particle beam therapy system that can scan charged particle beams at higher speeds. [Means for solving the problem]

[0008] A scanning electromagnet control system according to one aspect of the present disclosure is a scanning electromagnet that deflects a charged particle beam by applying a magnetic field generated by a plurality of windings, each having one end connected to the other, to the charged particle beam, and includes a control unit that, when fixing the direction of the charged particle beam, applies a constant voltage corresponding to the direction to each other end of each winding of the scanning electromagnet, and when changing the direction of the charged particle beam, applies a fluctuating voltage to each other end of each winding, such that the potential difference between the other ends is greater than the potential difference before and after the change in direction. [Effects of the Invention]

[0009] According to the present invention, it becomes possible to scan charged particle beams at higher speeds. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows a scanning electromagnet and scanning electromagnet control system according to a first embodiment of the present disclosure. [Figure 2] This figure shows an example of an excitation current target value table. [Figure 3] This is a diagram showing the equivalent circuit of a scanning electromagnet. [Figure 4] This figure shows an example of winding excitation current and applied voltage. [Figure 5] This is a diagram showing the configuration of a particle beam therapy system. [Figure 6] This diagram provides a more detailed explanation of the irradiation nozzle and its surrounding equipment. [Figure 7] This is a schematic diagram showing a cross-section of a scanning electromagnet. [Figure 8] This is a diagram illustrating scanning irradiation. [Figure 9] This figure shows an example of a depth-direction dose distribution in which an enlarged Bragg peak was formed. [Figure 10] This is a flowchart illustrating an example of a charged particle beam irradiation process. [Figure 11] This is a timing chart illustrating an example of a charged particle beam irradiation process. [Modes for carrying out the invention]

[0011] Embodiments of this disclosure will be described below with reference to the drawings. In the following, components having the same function will be denoted by the same reference numerals, and their descriptions may be omitted.

[0012] (First embodiment) Figure 1 shows a scanning electromagnet 1 and a scanning electromagnet control system 2 according to the first embodiment of the present disclosure.

[0013] The scanning electromagnet 1 has a cylindrical shape and is a scanning element that scans a charged particle beam by deflecting the charged particle beam passing through its internal space (columnar space). Specifically, the scanning electromagnet 1 has a plurality of sets of windings, and by adjusting the excitation current supplied to each winding, the direction and magnitude of the magnetic field generated in each winding are adjusted, whereby the direction of the charged particle beam changes. In the present embodiment, the scanning electromagnet 1 has three sets of windings (windings U, V, and W), and one end (hereinafter referred to as the terminal) of each of the windings U, V, and W is connected to each other.

[0014] The scanning electromagnet control system 2 is a control device that controls the scanning electromagnet 1 to scan a charged particle beam. The scanning electromagnet control system 2 includes a DC power supply 21, a winding U drive circuit 22U, a winding V drive circuit 22V, a winding W drive circuit 22W, a command conversion device 23, and a scanning electromagnet control device 24.

[0015] The DC power supply 21 is a power supply unit that generates power for applying an excitation current to each of the windings U, V, and W of the scanning electromagnet 1. In the present embodiment, an excitation current is applied to each of the windings U, V, and W of the scanning electromagnet 1 by a single DC power supply 21. The negative terminal of the DC power supply 21 is connected to a ground conductor, and the positive terminal is connected to the winding U drive circuit 22U, the winding V drive circuit 22V, and the winding W drive circuit 22W. The DC power supply 21 supplies power for applying an excitation current to the windings U, V, and W to the winding U drive circuit 22U, the winding V drive circuit 22V, and the winding W drive circuit 22W.

[0016] The winding U drive circuit 22U, the winding V drive circuit 22V, the winding W drive circuit 22W, the command conversion device 23, and the scanning electromagnet control device 24 constitute a control unit that controls the excitation current of the windings U, V, and W using the power from the DC power supply 21.

[0017] The winding U drive circuit 22U, winding V drive circuit 22V, and winding W drive circuit 22W are each connected to the starting end, which is a different end (other end) from the termination end of windings U, V, and W. Furthermore, each of the winding U drive circuit 22U, winding V drive circuit 22V, and winding W drive circuit 22W is connected to the ground conductor. Hereinafter, the winding U drive circuit 22U, winding V drive circuit 22V, and winding W drive circuit 22W may be collectively referred to as the winding drive circuit 22.

[0018] The winding drive circuit 22 uses power supplied from the DC power supply 21 to drive the windings U, V, and W of the scanning electromagnet 1, generating a scanning magnetic field, which is a magnetic field for deflecting the charged particle beam, in the windings U, V, and W. In this embodiment, the winding drive circuit 22 applies an excitation current to the windings U, V, and W by applying a voltage to the starting end of each winding U, V, and W using PWM (Pulse Width Modulation) control.

[0019] The command conversion device 23 and the scanning electromagnet control device 24 may be composed of a processor. The scanning electromagnet control device 24 may further include a digital circuit. For example, the processor constituting the scanning electromagnet control device 24 controls the winding drive circuit 22 via the digital circuit by controlling the digital circuit by executing a program stored in the memory of the scanning electromagnet control system 2 or a program read from an external source.

[0020] The command conversion device 23 receives an irradiation pattern file from a higher-level control system (not shown) that indicates an irradiation pattern for irradiating with a charged particle beam (charged particle beam). The irradiation pattern file indicates, as an irradiation pattern, the energy of the charged particle beam irradiated onto each irradiation spot, and the x and y coordinate values ​​(X,Y) of the irradiation position, which is the position of the irradiation spot. In this embodiment, the depth direction is the z direction, and the directions approximately perpendicular to the z direction are the x and y directions. Furthermore, as will be described later, the irradiation position in the z direction of the irradiation spot is determined by the energy of the charged particle beam.

[0021] The command conversion device 23 calculates a target current, which is the target value of the excitation current supplied to windings U, V, and W, for each irradiation spot based on the irradiation pattern file, and stores it as an excitation current target value table. The command conversion device 23 also inputs the excitation current target value table to the scanning electromagnet control device 24.

[0022] Figure 2 shows an example of an excitation current target value table. The excitation current target value table 200 shown in Figure 2 has a record for each irradiation spot, and each record has fields 201 to 203. Field 201 stores the energy of the charged particle beam irradiating the irradiation spot. Field 202 stores the xy coordinate value (X,Y) of the irradiation spot. Field 203 stores the target current, which is the target value of the excitation current supplied to windings U, V, and W at the irradiation spot. The excitation currents supplied to windings U, V, and W are denoted as lu, lv, and lw, respectively, and their target value is lu * lv * and lw * It is sometimes written as follows.

[0023] Returning to the explanation of Figure 1, the scanning electromagnet control device 24 controls the winding drive circuit 22 based on the excitation current target value table from the command conversion device 23. Specifically, the scanning electromagnet control device 24 determines the target voltage, which is the target value of the applied voltage applied to the starting ends of each of the windings U, V, and W, based on the excitation current target value table, and causes the winding drive circuit 22 to apply a voltage with that target value to the windings U, V, and W.

[0024] The following provides a more detailed explanation of the method for determining the target voltage.

[0025] Figure 3 is a diagram illustrating the method for determining the applied voltage and shows the equivalent circuit of scanning electromagnet 1. As shown in Figure 3, the self-inductances of windings U, V, and W are Lu, Lv, and Lw, respectively, and the resistances of windings U, V, and W are Ru, Rv, and Rw, respectively. The applied voltages applied to the starting ends of windings U, V, and W are Vu, Vv, and Vw, and the applied currents (excitation currents) supplied to windings U, V, and W are Iu, Iv, and Iw. Self-inductance and resistance are circuit constants.

[0026] The scanning electromagnet control device 24 determines two target voltages: a target voltage for when the direction of the charged particle beam is fixed and the irradiation position is stopped, and a target voltage for when the direction of the charged particle beam is changed and the irradiation position is moved. The target voltage for when the beam is fixed is a constant voltage corresponding to the direction of the charged particle beam. The target voltage for when the beam is moved is a fluctuating voltage that changes over time, and is a voltage where the potential difference between the starting ends of windings U, V, and W is greater than the potential difference before and after the change in the direction of the charged particle beam, i.e., before and after the movement of the irradiation position.

[0027] First, let's explain how to determine the target voltage at the time of stopping. In order to stop the irradiation position, it is necessary to keep the scanning magnetic field excited by the scanning electromagnet 1 constant, and therefore the applied current must also be kept constant. Consequently, the target voltage at the time of stopping is also constant. In this case, the relationship between the applied voltage and the applied current is expressed by the following equations 1 to 3 using the self-inductance and resistance of windings U, V, and W. (Equation 1) Vu - Vv = Ru·Iu - Rv·Iv (Equation 2) Vv - Vw = Rv·Iv - Rw·Iw (Equation 3) Vw - Vu = Rw·Iw - Ru·Iu

[0028] The scanning electromagnet control device 24 determines the target voltage at stop by inputting the target current corresponding to each irradiation spot as the applied current into equations 1 to 3 for each irradiation spot. Note that the self-inductance and resistance are circuit constants and are therefore common to each irradiation spot. Furthermore, since only the potential difference at the terminals of windings U, V, and W is determined from equations 1 to 3, the scanning electromagnet control device 24 determines the target voltage at stop by separately setting a reference potential. The method of setting the reference potential is not particularly limited; for example, the terminal with the lowest potential may be set to the ground potential, the terminal with the highest potential may be set to the positive terminal side potential of the DC power supply 21, or an intermediate potential may be set to the ground potential.

[0029] Next, we will explain how to determine the target voltage during movement. Since the target current corresponding to each irradiation spot is different, in order to move the irradiation position, it is necessary to change the applied current by changing the voltage applied to windings U, V, and W. For this reason, when the irradiation position is moved, back electromotive forces are induced by each winding U, V, and W. The back electromotive forces vu, vv, and vw induced by each winding U, V, and W are expressed by the following equations 4 to 6. (Formula 4) vu=-Lu ∆Iu / ∆t+M (∆Iv / ∆t+∆Iw / ∆t) (Formula 5) vv=-Lv ΔIv / Δt+M (ΔIw / Δt+ΔIu / Δt) (Formula 6) vw=-Lw ΔIw / Δt+M (ΔIu / Δt+ΔIv / Δt) Here, Δt is the travel time related to the movement of the irradiation position, M is the mutual inductance between each winding U, V, and W, and ΔIu, ΔIv, and ΔIw represent the difference in applied currents Iu, Iv, and Iw before and after the movement of the irradiation position. Note that the mutual inductance is set to be common among windings U, V, and W, but it may be a different value for each combination of windings U, V, and W.

[0030] Furthermore, let Vu_0s, Vv_0s, and Vw_0s be the voltages of windings U, V, and W, respectively, before the start of the irradiation position movement, and Vu_0f, Vv_0f, and Vw_0f be the voltages of windings U, V, and W, respectively, at the start of the irradiation position movement (immediately after the start of movement). Similarly, let Vu_1s, Vv_1s, and Vw_1s be the voltages of windings U, V, and W, respectively, after the completion of the irradiation position movement, and Vu_1f, Vv_1f, and Vw_1f be the voltages of windings U, V, and W, respectively, at the completion of the irradiation position movement (immediately before the completion of movement). In this case, the potential differences V1 to V3 between each winding U, V, and W at the start of the irradiation position movement and the potential differences V4 to V6 between each winding U, V, and W at the completion of the irradiation position movement are expressed by the following equations 7 to 12. (Formula 7)V1=Vu_0f-Vv_0f (Equation 8) V2 = Vv_0f - Vw_0f (Equation 9) V3 = Vw_0f - Vu_0f (Equation 10) V4 = Vu_1f - Vv_1f (Formula 11)V5=Vv_1f-Vw_1f (Equation 12) V6 = Vw_1f - Vu_1f

[0031] These potential differences V1 to V6 can be calculated from the following equations 13 to 18. (Equation 13) V1 = Ru·Iu_0 - Rv·Iv_0 - vu + vv (Formula 14)V2=Rv·Iv_0-Rw·Iw_0-vv+vw (Formula 15)V3=Rw·Iw_0-Ru·Iu_0-vw+vu (Formula 16)V4=Ru·Iu_1-Rv·Iv_1-vu+vv (Formula 17)V5=Rv·Iv_1-Rw·Iw_1-vv+vw (Formula 18)V6=Rw·Iw_1-Ru·Iu_1-vw+vu Here, Iu_0, Iv_0, and Iw_0 are the applied currents (target currents) flowing through windings U, V, and W before the irradiation position is moved, and Iu_1, Iv_1, and Iw_1 are the applied currents (target currents) flowing through windings U, V, and W after the irradiation position is moved. Furthermore, the first two terms on the right-hand side of each of equations 13 to 18 are steady-state terms determined from the applied currents before and after the irradiation position is moved, and the latter two terms are transient terms determined from the irradiation position change rate (ΔIu / Δt, ΔIv / Δt, and ΔIw / Δt), that is, the scanning rate that changes the direction of the charged particle beam.

[0032] The scanning electromagnet control device 24 determines the order of the absolute values ​​of the potential differences between the starting ends of each winding U, V, and W using equations 13 to 18. Then, the scanning electromagnet control device 24 determines the scanning speed by determining the change time Δt such that the potential difference Vm, which has the largest absolute value among the potential differences V1 to V6, matches a predetermined value. In this way, the scanning electromagnet control device 24 can determine the absolute values ​​of the potential differences between the starting ends of each winding U, V, and W at the start and completion of movement. Furthermore, the scanning electromagnet control device 24 determines the absolute value of the potential of each terminal by setting a reference potential. Then, the scanning electromagnet control device 24 determines the voltage at the starting end of each winding U, V, and W during the movement of the irradiation position from the start to the completion of movement by linearly interpolating the voltage at the starting end at the start of movement and the voltage at the starting end at the completion of movement. As a result, the scanning electromagnet control device 24 can achieve linear scanning in which the excitation current flowing through the starting ends of each winding U, V, and W changes at a constant rate over time from the start of movement to the end of movement. The predetermined value mentioned above is, for example, the input voltage Vin from the DC power supply 21 (the voltage on the positive side of the DC power supply 21).

[0033] Alternatively, the scanning electromagnet control device 24 may determine the change time Δt from a preset scanning speed. In this case, the scanning electromagnet control device 24 determines the potential differences V1 to V6 of each terminal at the start and completion of movement according to Equation 4-18. Furthermore, the scanning electromagnet control device 24 determines the absolute value of the potential of each terminal by setting a reference potential. The potential during movement can be linearly interpolated between the values ​​before and after movement to achieve linear scanning at the set scanning speed.

[0034] Figure 4 shows an example of the applied current and applied voltage to the winding U determined by the method described above. As shown in Figure 4, the applied voltage (target voltage during movement) 401 applied to the winding U when the irradiation position moves is greater than the applied voltages (target voltage at stop) Vu_0s and Vu_01 before and after the irradiation position moves. Also, the applied current 402 during movement changes at a constant rate over time, that is, it changes linearly. Therefore, the scanning electromagnet control device 24 determines the target voltage during movement such that the applied current changes linearly when the irradiation position moves.

[0035] Next, we will explain the particle beam therapy system using scanning electromagnet 1.

[0036] Figure 5 shows the configuration of a particle beam therapy system. The particle beam therapy system 10 shown in Figure 5 is a system that irradiates the affected area of ​​the patient 11, who is the target of irradiation, with a charged particle beam.

[0037] The particle beam therapy system 10 comprises a treatment table 40 on which a patient 11 is placed, an accelerator 41 for accelerating a charged particle beam, a beam transport device 42 which transports the charged particle beam accelerated by the accelerator 41, and an irradiation nozzle 43 for irradiating the affected area of ​​the patient 11 on the treatment table 40 with the charged particle beam transported by the beam transport device 42.

[0038] The accelerator 41 comprises an injector 44 and a synchrotron accelerator 45. The injector 44 injects charged particles into the synchrotron accelerator 45. The synchrotron accelerator 45 accelerates the charged particles injected from the injector 44 to about 60-70% of the speed of light and emits them to the outside as a charged particle beam. The beam transport device 42 is equipped with a deflection electromagnet 46 for deflecting the charged particle beam and transports the charged particle beam emitted from the accelerator 41 to the irradiation nozzle 43 while deflecting it with the deflection electromagnet 46. The irradiation nozzle 43 irradiates the affected area of ​​the patient 11 on the treatment table 40 with the charged particle beam from the beam transport device 42.

[0039] The particle beam therapy system 10 includes an overall control device 30, an accelerator / beam transport system control device 31, an irradiation nozzle control device 32, and a display 33 as a control system for controlling the irradiation of a charged particle beam.

[0040] The overall control unit 30, the accelerator / beam transport system control unit 31, and the irradiation nozzle control unit 32 may be composed of processors. In this case, the processors comprising the overall control unit 30, the accelerator / beam transport system control unit 31, and the irradiation nozzle control unit 32 execute various processes for controlling the irradiation of the charged particle beam by executing a program stored in the memory (not shown) of the particle beam therapy system 10 or a program read from an external source.

[0041] The overall control unit 30 controls the entire particle beam therapy system 10. The accelerator / beam transport system control unit 31 controls the accelerator 41 and beam transport system 42 according to instructions from the overall control unit 30. The irradiation nozzle control unit 32 controls the irradiation nozzle 43 according to instructions from the overall control unit 30. The irradiation nozzle control unit 32 includes the command conversion device 23 shown in Figure 1. The display 33 displays various information, such as the operating status of the particle beam therapy system 10.

[0042] Figure 5 shows the main components of the particle beam therapy system 10. In addition to the components shown in Figure 5, the particle beam therapy system 10 can be equipped with various other devices, such as peripheral equipment.

[0043] Figure 6 is a diagram illustrating the irradiation nozzle 43 and its surrounding equipment in more detail.

[0044] As shown in Figure 6, the irradiation nozzle 43 includes a scanning electromagnet 1, a dose monitor 60, a position monitor 61, a ridge filter 62, and a range shifter 63. A charged particle beam 90 is also injected into the irradiation nozzle 43.

[0045] The scanning electromagnet 1 scans the charged particle beam 90 in a two-dimensional plane substantially perpendicular to the direction of propagation of the charged particle beam 90, and irradiates the affected area 12 of the patient 11 with the scanned charged particle beam 90 via the dose monitor 60, position monitor 61, ridge filter 62, and range shifter 63.

[0046] Figure 7 schematically shows a cross-section of the scanning electromagnet 1 when it is cut by a plane substantially perpendicular to the direction of propagation of the charged particle beam 90, as viewed from the upstream side of the trajectory of the charged particle beam 90. In Figure 2, the direction of propagation of the charged particle beam 90 is defined as the Z direction.

[0047] As shown in Figure 7, the scanning electromagnet 1 comprises a cylindrical yoke 1a and windings U, V, and W provided inside the yoke 1a. The yoke 1a is made of a magnetic material such as iron.

[0048] In the example shown in Figure 7, grooves SL1 to SL6 are formed on the inner wall surface of the yoke 1a, recessed outward and extending in the z direction, at 60° intervals in a counterclockwise direction in this order. Windings U, V, and W are provided in grooves SL1 to SL6. For example, winding U is provided in grooves SL1 and SL4, which are located opposite each other; winding V is provided in grooves SL3 and SL6, which are located opposite each other; and winding W is provided in grooves SL2 and SL5, which are located opposite each other.

[0049] Returning to the explanation of Figure 6, the dose monitor 60 is a monitor for measuring the dose of the charged particle beam 90. It detects electrons generated as the charged particle beam 90 passes through and outputs a pulse signal corresponding to the detected electrons as a detection signal.

[0050] The position monitor 61 is a monitor for measuring the irradiation position of the charged particle beam 90. It detects electrons generated as the charged particle beam 90 passes through the monitor 61 at each position the charged particle beam 90 passes through, and outputs a pulse signal as a detection signal corresponding to the detected electrons at each passing position.

[0051] The ridge filter 62 is a filter for broadening the Bragg peak, which is the energy peak of the charged particle beam 90 within patient 11, in the depth direction. The range shifter 63 is a plate for adjusting the maximum depth to which the charged particle beam 90 reaches. The range shifter 63 is inserted into the scanning electromagnet 1 as needed.

[0052] Furthermore, dose monitor 60 and position monitor 61 are connected to dose monitor control devices 70 and position monitor control devices 71, respectively. Dose monitor control devices 70 and position monitor control devices 71 may be composed of processors. In this case, the processors comprising dose monitor control devices 70 and position monitor control devices 71 perform various processes by executing programs stored in the memory of the particle beam therapy system 10 or programs read from an external source.

[0053] The dose monitor control device 70 measures the irradiation dose from the charged particle beam 90 based on the detection signal output from the dose monitor 60 and outputs a dose signal indicating that irradiation dose. The position monitor control device 71 measures the position where the charged particle beam 90 passed through the position monitor 61 based on the detection signal output from the position monitor 61 and outputs a position signal indicating that position.

[0054] Furthermore, the dose monitor control device 70 and the position monitor control device 71 are connected to the irradiation nozzle control device 32. The irradiation nozzle control device 32 acquires the irradiation dose from the charged particle beam 90 based on the detection signal from the dose monitor control device 70. The irradiation nozzle control device 32 also calculates the position and width of the irradiation spot 81 based on the detection signal from the position monitor control device 71 to acquire the irradiation position of the charged particle beam 90. The irradiation nozzle control device 32 controls the irradiation of the charged particle beam 90 based on the irradiation dose and irradiation position.

[0055] Next, the operation of the particle beam therapy system 10 will be described. In this embodiment, the particle beam therapy system 10 irradiates with a charged particle beam 90 by scanning irradiation.

[0056] Figure 8 is a diagram illustrating scanning irradiation. As shown in Figure 8, in scanning irradiation, the affected area 12 is divided into multiple layers 80 arranged in the depth direction, and one or more irradiation spots 81 are placed in each layer 80. In addition, a treatment planning device (not shown) calculates the position of each irradiation spot 81 and the target irradiation dose for each irradiation spot 81 so that the affected area 12 is irradiated with a uniform dose, and generates this as treatment planning information. The particle beam therapy system 10 sequentially irradiates each layer 80 with charged particle beams 90 in a predetermined order to the irradiation spots 81 within that layer 80.

[0057] When the energy of the charged particle beam 90 changes, the destination of the charged particle beam 90 changes. Specifically, the higher the energy of the charged particle beam 90, the deeper it penetrates into the body. Therefore, changing the irradiation position in the depth direction of the affected area 12 is achieved by changing the energy of the charged particle beam 90. Consequently, the energy of the charged particle beam 90 differs from layer 80 to layer 80, and remains the same within the same layer 80.

[0058] Furthermore, in this embodiment, a charged particle beam is irradiated onto the affected area 12 in such a way that a spread-out Bragg peak (SOBP) is formed. SOBP is achieved by appropriately distributing the irradiation dose to each of a plurality of charged particle beams having different energies, resulting in a substantially uniform dose distribution in the depth direction.

[0059] Figure 9 shows an example of a dose distribution in the depth direction where an enlarged Bragg peak was formed. As shown in Figure 9, by appropriately distributing the irradiation dose to each of the multiple charged particle beams having different energies, each charged particle beam of each energy is irradiated with a dose distribution shown by the Bragg curve 85. As a result, multiple Bragg curves 85 corresponding to each energy are superimposed to form a dose distribution that is substantially uniform in the depth direction, as shown by the SOBP curve 86.

[0060] Figure 10 is a flowchart illustrating an example of the irradiation process of a charged particle beam by the particle beam therapy system 10. The treatment plan information, pre-generated by the treatment planning device described above, is transmitted from the treatment planning device to the Oncology Information System (OIS), which is not shown in the diagram, and stored in the OIS. Furthermore, the treatment plan information is transmitted from the OIS to the overall control device 30 of the particle beam therapy system 10, as shown in Figure 9.

[0061] In step S101, the overall control unit 30 receives treatment plan information from the OIS. At this time, the overall control unit 30 may display the treatment plan information and information indicating the operation of the particle beam therapy system 10 on the display 33.

[0062] In step S102, the overall control unit 30 sets instrument parameters for controlling the accelerator / beam transport system control unit 31, the irradiation nozzle control unit 32, and the treatment table 40 based on the treatment plan information. The overall control unit 30 controls the accelerator / beam transport system control unit 31, the irradiation nozzle control unit 32, and the treatment table 40 based on the instrument parameters.

[0063] For example, the overall control device 30 transmits the energy of the charged particle beam corresponding to each irradiation spot, the xy coordinate values ​​(X,Y) of the irradiation position, and the irradiation dose as instrument parameters to the irradiation nozzle control device 32. The irradiation nozzle control device 32 receives the instrument parameters and passes an irradiation pattern file corresponding to those instrument parameters to the command conversion device 23. Based on the irradiation pattern file, the command conversion device 23 calculates the target current for each winding U, V, and W for each irradiation spot and outputs it to the scanning electromagnet control device 24 as an excitation current target value table. Based on the excitation current target value table, the scanning electromagnet control device 24 calculates the target voltage for each winding U, V, and W. The target voltage includes the target voltage when each irradiation spot is stopped and the target voltage when moving between irradiation spots.

[0064] In step S103, the accelerator / beam transport system control device 31 and the irradiation nozzle control device 32 control the accelerator 41, beam transport device 42, and irradiation nozzle 43 according to the control of the overall control device 30. As a result, the charged particle beam is irradiated to the j-th irradiation spot in the i-th layer. At this time, the voltage applied to the starting ends of windings U, V, and W becomes a constant voltage corresponding to the position of the j-th irradiation spot.

[0065] i is an integer from 1 to K, and identifies the layer set in the affected area 12. j is an integer from 1 to M(i) for each layer of the affected area 12, and identifies the irradiation spot in that layer. For the first irradiation, i=1 and j=1. In addition, the integer M(i) identifies the last irradiation spot in the i-th layer, and the integer M(K) identifies the last irradiation spot in the last layer (i=K).

[0066] Step S104 is executed when the irradiation of the charged particle beam to the j-th irradiation spot in the i-th layer is completed. In step S104, the overall control device 30 determines whether the irradiation of the charged particle beam to the last irradiation spot in the current layer is completed. If the irradiation is completed, step S105 is executed; otherwise, step S107 is executed.

[0067] In step S105, the overall control device 30 determines whether the irradiation of the last layer with the charged particle beam has been completed. If the irradiation has not been completed, step S106 is executed; if the irradiation has been completed, step S107 is executed.

[0068] In step S106, the overall control device 30 controls the accelerator / beam transport system control device 31 and the irradiation nozzle control device 32 to perform a movement process to move the irradiation spot. At this time, the irradiation spot after the movement will be the (j+1)th irradiation spot in the i-th layer if the irradiation of the last irradiation spot in the current layer has not been completed (step S104: no), and the irradiation spot after the movement will be the first irradiation spot in the (i+1)th layer if the irradiation of the last layer has not been completed (step S105: no). In addition, during the movement process, the voltage applied to the starting ends of windings U, V and W will be the target voltage during movement calculated from the target voltage at stop corresponding to the irradiation spot before and after the movement.

[0069] In step S107, the overall control unit 30 stops the irradiation control of the charged particle beam and terminates the radiotherapy.

[0070] Figure 11 is a timing chart illustrating an example of a charged particle beam irradiation process. Figure 11 shows an example in which a charged particle beam is irradiated to three irradiation spots, from irradiation spot A to irradiation spot C.

[0071] As shown in Figure 11(a), for irradiation of irradiation spot A, an emission timing signal is output from the accelerator / beam transport system control device 31 to the accelerator 41 at times t1 to t2, and the charged particle beam is irradiated onto the affected area 12. Similarly, for irradiation of irradiation spot B, an emission timing signal is output from the accelerator / beam transport system control device 31 to the accelerator 41 at times t3 to t4, and for irradiation of irradiation spot C, an emission timing signal is output from the accelerator / beam transport system control device 31 to the accelerator 41 at times t5 to t6. Since the irradiation of irradiation spots A to C is performed by the same process, the following will mainly describe the irradiation of irradiation spot A.

[0072] When irradiating spot A, as shown in Figure 11(a), the discharge timing signal rises at time t1, and the irradiation of the charged particle beam begins as shown in Figure 11(b). Subsequently, the intensity of the charged particle beam increases, and at time ta, which is τ1 after time t1, the intensity of the charged particle beam reaches its maximum value. Then, as the discharge timing signal falls at time t2, the intensity of the charged particle beam decreases, and at time tb, which is τ2 after time t2, the intensity of the charged particle beam becomes 0. In other words, the irradiation of the charged particle beam ends.

[0073] Furthermore, when the emission timing signal rises at time t1, as shown in Figure 11(c), the dose monitor 60 in the irradiation nozzle 43 detects electrons generated by the passage of the charged particle beam and outputs a pulse signal corresponding to the detected electrons as a detection signal to the dose monitor control device 70. The dose monitor control device 70 counts the number of pulse signals, which are detection signals from the dose monitor 60, as the pulse count value. As a result, the pulse count value increases as shown in Figure 11(d). When the pulse count value reaches a predetermined value at time tc before time t2, the dose monitor control device 70 transmits an expiration signal to the irradiation nozzle control device 32. When the irradiation nozzle control device 32 receives the expiration signal, it stops irradiating irradiation spot A with the charged particle beam. Here, the predetermined value is determined according to the target irradiation dose of irradiation spot A.

[0074] Furthermore, when the emission timing signal rises at time t1, as shown in Figure 11(e), the position monitor 61 in the irradiation nozzle 43, similar to the dose monitor 60, detects electrons generated by the passage of the charged particle beam at each position the charged particle beam passes through, and outputs the pulse signal corresponding to the detected electrons at each passing position as a detection signal to the position monitor control device 71. The position monitor control device 71 counts the number of pulse signals at each passing position as a pulse count value.

[0075] Then, when irradiation of irradiation spot A is completed, the position monitor control device 71 outputs the pulse count value for the irradiation period of irradiation spot A to the irradiation nozzle control device 32. Based on the pulse count value from the position monitor control device 71, the irradiation nozzle control device 32 calculates the position and size of the irradiation spot to which the charged particle beam was actually irradiated, and determines whether or not the charged particle beam 90 was irradiated to the predetermined position based on that position and size. If the charged particle beam 90 was not irradiated to the predetermined position, that is, if the amount of deviation in the position or size of the irradiation spot exceeds a predetermined value, the overall control device 30 determines that there may be a malfunction and stops the irradiation of the charged particle beam.

[0076] Furthermore, when the irradiation nozzle control device 32 receives an expiration signal from the dose monitor control device 70, the command converter 23 of the irradiation nozzle control device 32 determines the target current corresponding to the irradiation position of the next irradiation spot and transmits it to the scanning electromagnet control device 24. Upon receiving the target current, the scanning electromagnet control device 24 calculates the target voltage at stop corresponding to the next irradiation spot and the target voltage during movement to the next irradiation spot based on the target current, and applies the target voltage during movement to the starting ends of windings U, V, and W to control the excitation current flowing through windings U, V, and W.

[0077] Figure 11(f) shows the changes in the excitation current flowing through windings U, V, and W. From time t1, when the emission timing signal rises, until time tc, when it begins to fall, the excitation current is constant. During this time, the xy coordinates (X,Y) of the irradiation position are constant. From time tc until time t3, when the emission timing signal rises for irradiation of the next irradiation spot B, the excitation current approaches the target current at the next irradiation spot B at a constant rate over time, reaching the target current at time t3. During this time, the xy coordinates (X,Y) of the irradiation position change.

[0078] While the irradiation of irradiation spot A with a charged particle beam was described here, the irradiation of irradiation spots B and C with a charged particle beam is carried out using a similar process.

[0079] As described above, according to this embodiment, the scanning electromagnet 1 deflects the charged particle beam by applying a magnetic field generated by multiple windings U, V, and W whose ends are connected to each other to the charged particle beam. When fixing the direction of the charged particle beam, the scanning electromagnet control system 2 applies a constant voltage corresponding to the direction to each of the starting ends of each winding U, V, and W of the scanning electromagnet 1. When changing the direction of the charged particle beam, it applies a fluctuating voltage to each of the starting ends of each winding U, V, and W such that the potential difference between the starting ends becomes greater than the potential difference before and after the change in direction. Therefore, when changing the direction of the charged particle beam, the potential difference between windings U, V, and W becomes greater than the potential difference before and after the change in direction of the charged particle beam, making it possible to reduce the effect of back electromotive force caused by the change in the excitation current flowing through windings U, V, and W on the scanning speed. As a result, it becomes possible to scan the charged particle beam at a higher speed.

[0080] Furthermore, in this embodiment, the scanning electromagnet control system 2 determines the fluctuating voltage for changing the direction of the charged particle beam based on the target voltage before and after the change in the direction of the charged particle beam, the excitation current flowing through each winding U, V, and W, and the scanning speed for changing the direction of the charged particle beam. This makes it possible to more appropriately reduce the influence of back electromotive force on the scanning speed.

[0081] Furthermore, in this embodiment, the scanning electromagnet control system 2 determines the value of the fluctuating voltage at the start of movement, when the direction of the charged particle beam is to be changed, based on the target voltage at stop before the direction of the charged particle beam is changed and the scanning speed. It also determines the value of the fluctuating voltage at the end of movement, when the direction of the charged particle beam is to be changed, based on the target voltage at stop after the direction of the charged particle beam is changed and the scanning speed. In addition, the scanning electromagnet control system 2 determines the value of the fluctuating voltage from the start of movement to the end of movement based on the value of the fluctuating voltage at the start of movement and the value of the fluctuating voltage at the end of movement. This makes it possible to more appropriately reduce the influence of back electromotive force on the scanning speed.

[0082] Furthermore, in this embodiment, the scanning electromagnet control system 2 determines the value of the fluctuating voltage from the start of movement to the end of movement by linearly interpolating the value of the fluctuating voltage at the start of movement and the value of the fluctuating voltage at the end of movement. This makes it possible to linearly change the excitation current from the start of movement to the end of movement, thereby enabling scanning of the charged particle beam along a linear trajectory at a constant speed.

[0083] Furthermore, in this embodiment, the scanning electromagnet control system 2 determines the value of the fluctuating voltage from the start to the end of movement so that the excitation current flowing through each winding U, V, and W changes at a constant rate over time. Therefore, it becomes possible to scan the charged particle beam along a straight trajectory at a constant speed.

[0084] Furthermore, in this embodiment, since a single DC power supply 21 is used to apply voltage to multiple windings U, V, and W, it becomes possible to reduce the effect of back electromotive force on the scanning speed with a simple device configuration.

[0085] Furthermore, in this embodiment, there are three winding systems: windings U, V, and W. Therefore, it is possible to scan the charged particle beam two-dimensionally with a simple device configuration.

[0086] (Second embodiment) In this embodiment, the method of applying voltage to windings U, V, and W when the irradiation position is moved differs from that of the first embodiment.

[0087] Hereinafter, for each winding U, V, and W, the terminal on the higher potential side of the two starting points to which the potential difference Vm with the maximum absolute value among the potential differences V1 to V6 represented by equations 13 to 18 is applied will be defined as T1, and the terminal on the lower potential side as T2. In addition, for each winding U, V, and W, the starting point other than starting points T1 and T2 will be defined as T3.

[0088] In this embodiment, the scanning electromagnet control device 24 uses equations 13 to 18 to determine the potential difference Vm that has the maximum absolute value among the potential differences V1 to V6. Then, when the movement of the irradiation position begins, the scanning electromagnet control device 24 continuously connects the high-potential side of the DC power supply 21 to the starting point T1 and continuously grounds the starting point T2 for a certain time Δt'. As a result, the potential difference between the starting points T1 and T2 is set to the potential difference of the DC power supply 21 (the potential difference between the positive and negative electrodes). Furthermore, for the starting point T3, the scanning electromagnet control device 24 applies a voltage according to a target voltage obtained by linearly interpolating the fluctuating voltage values ​​before and after the movement, similar to Embodiment 1.

[0089] After time Δt' has elapsed, the scanning electromagnet control device 24 performs feedback control of the excitation current to adjust the voltage values ​​applied to the starting ends of windings U, V, and W so that the excitation current becomes the target current after the movement is complete.

[0090] The above time Δt' may be determined, for example, based on the distance traveled by the irradiation position, or it may be determined as the time it takes for the current flowing at a given starting point to reach the target current.

[0091] As described above, according to this embodiment, the voltage of the DC power supply 21 can be efficiently applied to the starting point where a large potential difference is required, thus enabling high-speed scanning.

[0092] This disclosure is not limited to the embodiments described above, but includes various modifications. For example, the embodiments described above are for illustrative purposes only, and this disclosure is not necessarily limited to having all the configurations described.

[0093] Furthermore, a part of the configuration of one embodiment may be replaced with a part of the configuration of another embodiment, and a part of the configuration of one embodiment may be added to a part of the configuration of another embodiment. In addition, a part of the configuration of each embodiment may be added, deleted, or replaced with a part of another configuration.

[0094] Furthermore, while the above method employs a discrete spot irradiation method in which the charged particle beam is stopped between irradiation spots, a continuous spot irradiation method that does not stop the charged particle beam between irradiation spots may also be employed.

[0095] Furthermore, accelerator 41 is not limited to synchrotron accelerator 45; various known accelerators such as cyclotron accelerators or synchrocyclotron accelerators may be used. Also, the charged particles accelerated by accelerator 41 may be protons or heavy particles such as carbon.

[0096] Furthermore, the scanning electromagnet 1 in each embodiment is not limited to the irradiation nozzle 43, but may also be provided in the accelerator 41 and beam transport device 42, etc. In other words, the scanning electromagnet 1 may be used in the accelerator 41 and beam transport device 42 for the purpose of correcting the trajectory of the charged particle beam 90.

[0097] Furthermore, in devices such as the command conversion device 23, the scanning electromagnet control device 24, the overall control device 30, the accelerator / beam transport system control device 31, and the irradiation nozzle control device 32, as well as in the distribution analysis device 113, irradiation control device 104, data server 111, and treatment planning device 112, processing may be shared among multiple processors or computer systems, or some physical components (such as databases) may be connected via a network.

[0098] The embodiments of the Disclosure described above are illustrative for illustrative purposes and are not intended to limit the scope of the Disclosure to those embodiments only. Those skilled in the art can implement the Disclosure in various other forms without departing from the scope of the Disclosure. [Explanation of symbols]

[0099] 1: Scanning electromagnet 1a: Yoke 2: Scanning electromagnet control system 10: Particle beam therapy system 11: Patient 12: Affected area 21: DC power supply 22: Winding drive circuit 22U: Winding U drive circuit 22V: Winding V drive circuit 22W: Winding W drive circuit 23: Command conversion device 24: Scanning electromagnet control device 26: DC power supply 30: Overall control device 31: Beam transport system control device 32: Irradiation nozzle control device 33: Display 40: Treatment table 41: Accelerator 42: Beam transport device 43: Irradiation nozzle 44: Injector 45: Synchrotron accelerator 46: Deflection electromagnet 60: Dose monitor 61: Position monitor 62: Ridge filter 63: Range shifter 70: Dose monitor control device 71: Position monitor control device U~W: Winding

Claims

1. A scanning electromagnet control system that controls a scanning electromagnet that deflects a charged particle beam by applying a magnetic field generated by multiple windings, each having one end connected to the other, to the charged particle beam, The control unit has the following functions: when fixing the direction of the charged particle beam, it applies a constant voltage corresponding to the direction to each other end of each winding of the scanning electromagnet; and when changing the direction of the charged particle beam, it applies a fluctuating voltage to each other end of each winding, such that the potential difference between the other ends is greater than the potential difference before and after the change in direction. The control unit calculates the back electromotive force generated in each winding based on the scanning speed at which the orientation is changed, the self-inductance of each winding, and the mutual inductance between each winding and the windings of other systems, and determines the fluctuating voltage based on the back electromotive force and the current flowing through each winding due to the constant voltage before and after the orientation change, in a scanning electromagnet control system.

2. The scanning electromagnet control system according to claim 1, wherein the control unit determines the value of the fluctuating voltage at the start of the change of direction based on the constant voltage and the back electromotive force before the change of direction, determines the value of the fluctuating voltage at the end of the change of direction based on the constant voltage and the back electromotive force after the change of direction, and determines the value of the fluctuating voltage between the start and the end based on the value of the fluctuating voltage at the start and the value of the fluctuating voltage at the end.

3. The scanning electromagnet control system according to claim 2, wherein the control unit determines the value of the fluctuating voltage between the start time and the end time by linearly interpolating the value of the fluctuating voltage at the start time and the value of the fluctuating voltage at the end time.

4. The scanning electromagnet control system according to claim 2, wherein the control unit determines the value of the fluctuating voltage from the start to the end of the period such that the excitation current flowing through each of the other ends changes at a constant rate over time from the start to the end of the period.

5. The system further includes a DC power supply that generates the voltage applied to each winding, The scanning electromagnet control system according to claim 1, wherein the control unit sets the potential difference between the other ends of two predetermined windings among the windings to the potential difference of the DC power supply when the change of direction is initiated, and then adjusts the value of the fluctuating voltage applied to each winding so that the current flowing through the other end of each winding becomes the target current.

6. It further has a single DC power supply, The scanning electromagnet control system according to claim 1, wherein the control unit applies voltage to each winding using the DC power supply.

7. The aforementioned winding has three systems, according to the scanning electromagnet control system of claim 1.

8. A scanning electromagnet control system for controlling a scanning electromagnet that deflects a charged particle beam by applying a magnetic field generated by multiple windings, each having one end connected to the other, to the charged particle beam, wherein the scanning electromagnet controls the scanning electromagnet that deflects the charged particle beam. When fixing the direction of the charged particle beam, a constant voltage corresponding to the direction is applied to each of the other ends of each winding of the scanning electromagnet. When changing the direction of the charged particle beam, a fluctuating voltage is applied to each of the other ends of each winding such that the potential difference between the other ends is greater than the potential difference before and after the change in direction. A scanning electromagnet control method, wherein when the fluctuating voltage is applied, the back electromotive force generated in each winding is calculated based on the scanning speed at which the direction is changed and the self-inductance of each winding and the mutual inductance between each winding and the windings of other systems, and the fluctuating voltage is determined based on the back electromotive force and the current flowing through each winding due to the constant voltage before and after the change in direction.

9. A particle beam therapy system comprising an accelerator that emits charged particle beams, a transport device that transports the charged particle beams emitted from the accelerator, and an irradiation nozzle that irradiates a patient with the charged particle beams transported by the transport device, A scanning electromagnet is provided in at least one of the accelerator, the transport device, and the irradiation nozzle, and deflects the charged particle beam by applying a magnetic field generated by a plurality of windings, one end of which is connected to the other, to the charged particle beam. The scanning electromagnet control system includes, when fixing the direction of the charged particle beam, a constant voltage corresponding to the direction is applied to each other end of each winding of the scanning electromagnet, and when changing the direction of the charged particle beam, a fluctuating voltage is applied to each other end of each winding so that the potential difference between the other ends is greater than the potential difference before and after the change in direction. The scanning electromagnet control system calculates the back electromotive force generated in each winding based on the scanning speed at which the orientation is changed and the self-inductance of each winding and the mutual inductance between each winding and other windings, and determines the fluctuating voltage based on the back electromotive force and the current flowing through each winding due to the constant voltage before and after the orientation change, in a particle beam therapy system.

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