JP2018143680A - Particle beam therapeutic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize accurate irradiation by distributing delay ray dosage onto a final spot during scanning irradiation with successive beam to another spot.SOLUTION: It comprises an accelerator accelerating charged particle beam, an irradiation nozzle irradiating the accelerated-charged particle beam, and a controlling apparatus controlling the accelerator and the irradiation nozzle. The irradiation nozzle comprises a scan electromagnet scanning a plurality of spots set on an irradiation target with the charged particle beam and a ray dosage monitor measuring irradiation dose of the charged particle beam. The controlling apparatus executes a control where electric current instruction value of the scan electromagnet is changed after a predetermined time period from detection of spot ray dosage satisfaction signal from the ray dosage monitor.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a particle beam therapy system that performs cancer treatment by irradiating a cancer affected area with a charged particle beam accelerated by a particle beam accelerator such as a synchrotron or a cyclotron.

  In particle beam therapy, a charged particle beam accelerated by an accelerator called synchrotron or cyclotron is transported to the treatment room by a beam transport system, and irradiated to the affected part of the patient lying on the bed in the treatment room to treat cancer. Do. The charged particle beam is irradiated after the beam is appropriately shaped so that it can be irradiated to different cancer affected areas by the irradiation nozzle. For example, Patent Literature 1, Non-Patent Literature 1, and Non-Patent Literature 2 describe methods for forming an appropriate dose distribution.

Japanese Patent No. 5496414

T. Inaniwa, et al. “Optimization for fast-scanning irradiation in particle therapy”, Med. Phys. 34 (2007) 3302-3311. T. Furukawa, et al. “Design study of a raster scanning system for moving target projection in heavy-ion radiotherapy”, Med. Phys. 34 (2007) 1085-1097.

  When irradiating a charged particle beam, an irradiation method that scatters the beam from the accelerator with a scatterer and shapes the beam shape with a collimator etc. according to the affected area, or an irradiation method that enables highly accurate irradiation that matches the affected area shape more There is a method such as scanning irradiation in which a beam is scanned in a two-dimensional plane in the X direction and Y direction by a pair of electromagnets called scanning electromagnets, and irradiation is performed while scanning a thin beam from an accelerator.

  In scanning irradiation, there are a plurality of irradiation methods for irradiating an affected area with a uniform dose. In the scanning irradiation method called discrete spot irradiation, an irradiation spot that irradiates the affected part with a beam is arranged, and when a predetermined irradiation amount of each irradiation spot is reached, the beam is temporarily turned off, moved to the next spot, and re-beamed. It is an irradiation method that repeats turning on and performing irradiation. In discrete spot irradiation, a beam is turned on / off at each spot, and the beam is irradiated while scanning is stopped at the spot. In discrete spot irradiation, the irradiation position, energy, and irradiation amount of a spot are determined in advance by a treatment planning device before treatment. When each spot is irradiated by the discrete spot irradiation method, the irradiation position and irradiation amount of the charged particle beam are measured, and the beam is irradiated to the predetermined irradiation spot by a predetermined irradiation amount. To change the energy in the depth direction of the affected area, the energy of the charged particle beam is changed by changing the amount of an energy absorber called a range shifter in the accelerator or irradiation nozzle to change the irradiation spot in the depth direction.

  For discrete spot irradiation, there is an irradiation method called continuous beam irradiation in which the beam is not turned on / off for each spot. This is the same as discrete spot irradiation in that it moves to the next irradiation spot when the prescribed dose expires at the irradiation spot, but it moves while irradiating the beam without turning off the beam while moving the irradiation spot. This is an irradiation method characterized by In scanning irradiation with a continuous beam, the beam is also irradiated between spots. Therefore, unlike the discrete spot irradiation, it is necessary to determine the route for irradiating the irradiation spot irradiated with the same energy in the treatment plan. In addition, since the beam is also irradiated between spots, the beam intensity of the accelerator is controlled so that irradiation with a continuous beam in advance in the treatment plan is performed so as not to irradiate more than a predetermined dose during movement between spots. It is necessary to determine the beam intensity. The energy change in the depth direction is the same with no particular differences between discrete spot irradiation and continuous beam irradiation.

  As described above, scanning irradiation is an irradiation method in which an affected area is irradiated while directly scanning a thin beam from an accelerator.

  In scanning irradiation with a continuous beam, a spot is irradiated along a one-stroke writing scanning path. Since there is a finite response time for beam blocking at the final spot in the same layer, the dose may increase locally and the dose will increase. This had an adverse effect on the dose distribution at the place where it was originally intended to be irradiated with a uniform dose.

  In order to solve the above problems, for example, the configuration described in the claims is adopted.

  The present invention includes a plurality of means for solving the above-mentioned problems. For example, an accelerator that accelerates a charged particle beam, an irradiation nozzle that irradiates the accelerated charged particle beam, the accelerator, and the accelerator. A control device that controls the irradiation nozzle, and the irradiation nozzle includes a scanning electromagnet that scans a plurality of spots set to be irradiated with the charged particle beam, and a dose monitor that measures an irradiation amount of the charged particle beam. And the control device controls to change the current command value of the scanning electromagnet after a predetermined time has elapsed after detecting the spot dose expiration signal from the dose monitor.

  According to the present invention, since the delayed dose of the final spot of scanning irradiation by a continuous beam can be dispersed to other spots, it is possible to perform irradiation with high accuracy.

It is a figure which shows the whole structure of a particle beam therapy system. It is a figure which shows a particle beam scanning irradiation nozzle. It is a figure which shows a charged particle beam and an irradiation spot when scanning the affected part by scanning. It is a figure which shows dose distribution of a depth direction. It is a figure which shows the scanning path | route of one stroke writing of the scanning irradiation by a continuous beam. It is a figure which shows a time chart. It is a figure which shows the time chart by this invention.

  Specific modes for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an overall configuration of a particle beam therapy system according to an embodiment of the present invention. The particle beam therapy system includes an accelerator 20 that accelerates a charged particle beam (hereinafter referred to as a beam) 90, a beam transport system 30 that transports the accelerated beam 90 to an irradiation nozzle, an irradiation nozzle 40 that irradiates the affected area with a beam, A treatment table 50, a treatment plan device 10 for creating a treatment plan, an overall control device 11, an accelerator / beam transport system control device 12, and an irradiation nozzle control device 13 are provided. The accelerator 20 includes an injector 21 and a synchrotron accelerator 22. The beam 90 accelerated to 60 to 70% of the speed of light by the accelerator 20 is transported to the irradiation nozzle 40 while being bent in a vacuum by a magnetic field by the deflecting electromagnet 31 disposed in the beam transport system 30. The beam 90 is shaped by the irradiation nozzle 40 so as to match the shape of the irradiation region, and is irradiated to the irradiation target. The irradiation target is, for example, the affected part 51 of the patient 5 lying on the treatment table 50.

  FIG. 2 shows an irradiation nozzle 40 for particle beam scanning according to an embodiment of the present invention. In the irradiation nozzle 40, the beam 90 is scanned in a two-dimensional plane by the horizontal and vertical scanning electromagnets 41A and 41B. The affected part 51 is irradiated with the beam 90 scanned by the scanning electromagnets 41 </ b> A and 41 </ b> B. The dose monitor 42 measures the irradiation amount of the beam 90 irradiated to each irradiation spot. The dose monitor controller 72 controls the amount of irradiation with which each irradiation spot is irradiated. The position monitor 43 measures the beam position (for example, the position of the center of gravity) of each irradiation spot. The position monitor control device 73 calculates the position and width of the irradiation spot based on the beam position data measured by the position monitor 43 and confirms the irradiation position of the beam 90. The ridge filter 44 is used when necessary to thicken the Bragg peak. Further, the arrival position of the beam 90 may be adjusted by inserting the range shifter 45.

In the scanning irradiation, the position of the irradiation spot for irradiating the affected area with a uniform dose by the treatment planning apparatus 10 shown in FIG. 1 and the target irradiation amount for each irradiation spot are calculated in advance. FIG. 3 shows a schematic diagram when the affected area is irradiated by particle beam scanning irradiation. The affected part 51 is divided into a plurality of layers 52, and each layer 52 is irradiated with a beam 90 having the same energy. A plurality of irradiation spots 53 are arranged in the layer 52.
Data for each patient calculated by the treatment planning device 10 shown in FIG. 1 is sent to the overall control device 11 of the particle beam treatment system shown in FIG. The overall control device 11 outputs energy change, beam emission signal, or emission stop signal to the accelerator / beam transport system control device 12. The coordinate value and irradiation amount of each irradiation spot are sent from the overall control device 11 to the irradiation nozzle control device 13. The coordinate value of the irradiation spot is converted into the excitation current value of the scanning electromagnets 41A and 41B and sent to the scanning electromagnet power supply control device 71 shown in FIG.

  When a predetermined irradiation dose of the beam 90 is irradiated to a certain irradiation spot 53 arranged by the treatment planning apparatus, the next irradiation spot 53 is irradiated. When irradiation of a certain layer 52 is completed, irradiation of the next layer 52 is performed. First, the beam energy is changed to change the irradiation position in the beam traveling direction, that is, in the affected part depth direction. Or you may change the thickness of the range shifter 45 which is an energy absorber in the irradiation nozzle 40. FIG. When the energy of the beam changes, the position where the beam reaches the body changes. A charged particle beam having a high energy reaches a deep position in the body, and a charged particle beam having a low energy reaches only a shallow position in the body. In particle beam scanning irradiation, in order to form a uniform dose distribution in the depth direction, the energy of the beam is changed for each layer, and the irradiation dose for each energy is appropriately distributed to achieve SOBP ( Spread Out Bragg Peak). By appropriately allocating the irradiation amount of each energy, the Bragg curve 81 of each energy is overlapped to form a uniform dose distribution SOBP 82 in the depth direction as shown in FIG.

  Next, the horizontal irradiation of scanning irradiation will be described. In the treatment planning apparatus 10, an irradiation spot 53 for irradiating the affected area with a uniform dose is arranged for each beam energy as shown in FIG. An irradiation method in which the beam is irradiated without moving on and off for each spot when moving the irradiation spot 53 is called continuous beam irradiation. In addition, when moving the irradiation spot 53, a method in which the beam is once turned off and then moved to the next spot, and the beam is turned on again to irradiate the next spot is called discrete spot irradiation. In this embodiment, scanning is performed by continuous beam irradiation.

  In a treatment plan using a continuous beam, a beam is also irradiated between irradiation spots, so it is necessary to determine the scanning path of the charged particle beam. FIG. 5 shows an example of a scanning path of the layer 52 having a certain energy in scanning irradiation with a continuous beam. In FIG. 5, a point represents an irradiation spot, and a straight line represents a one-stroke scanning path. As shown in FIG. 5, in scanning with a continuous beam, beam irradiation is performed between irradiation spots, so it is necessary to determine a scanning path so that adjacent spots can be efficiently irradiated with a one-stroke writing scanning path. This is because if the scanning path is not optimized, not only the dose for each spot can be managed, but also an extra area other than the affected area is irradiated.

  The method for determining the scanning path is preferably determined using a traveling salesman algorithm so that the scanning distance when all the irradiation spots 53 are scanned is minimized. Further, in order to manage the irradiation amount irradiated between the irradiation spots 53, it is necessary to determine the beam intensity. In continuous beam irradiation, the dose while moving between the irradiation spots 53 is also measured by the dose monitor 42, and the stopped irradiation amount and the moving irradiation amount are added to the irradiation spot to be stopped next. Because it becomes the irradiation amount irradiated to the spot, if the beam intensity becomes too large due to fluctuation during movement between spots, the irradiation amount of the spot to stop next between the irradiation spots will expire, so the treatment planning device Therefore, it is necessary to determine an appropriate beam intensity that does not expire between irradiation spots in consideration of the change width of the beam intensity. Non-Patent Document 1 discloses a technique for creating a treatment plan for continuous beam irradiation in consideration of the dose between spots. Non-Patent Document 2 discloses a technique of continuous beam irradiation based on an accelerator operation in which beam intensity is controlled.

  FIG. 6 shows a time chart when the irradiation spot 53 shown in FIG. 5 is irradiated with a continuous beam. FIG. 5 shows a large number of irradiation spots and scanning paths, but the time chart of FIG. 6 shows an example of irradiation with three spots. FIG. 6 shows three types of time charts at the top and bottom, showing from the top the beam intensity of the accelerator, the integrated value of the dose measured by the dose monitor 42, and the time change of the current applied to the scanning electromagnet power source.

  In FIG. 6, the beam intensity of the accelerator is first controlled to be constant (denoted as beam intensity I in FIG. 6) based on the command value when the beam is turned on at spot 1, and irradiation ends at spot 3. Until then, the beam intensity has a constant value determined in the treatment plan. Therefore, the integrated dose of the dose monitor 42 increases linearly with time. Assuming that the irradiation doses of the spots 1, 2, and 3 are Q1, Q2, and Q3, respectively, the dose monitor control device 72 has the accumulated value of each spot in the memory. That is, the dose expiration values of the spots 1, 2, and 3 are Q1, Q1 + Q2, and Q1 + Q2 + Q3, respectively. When the integrated measurement value of the dose monitor 42 reaches the expiration values of the spots 1, 2, and 3, a dose expiration signal is sent from the dose monitor control device 72 to the irradiation nozzle control device 13. In FIG. 6, the time when the doses of the spots 1, 2, and 3 expire is indicated as t1, t2, and t3, respectively. The irradiation nozzle control device 13 receives this expiration signal, sends a signal for moving to the next spot to the scanning electromagnet power supply control device 71, and the current of the scanning electromagnet power supplies 61A and 62A changes based on that signal and moves to the next spot. To start.

  A first embodiment for carrying out the present invention will be described with reference to FIG.

  In FIG. 7, the time change of the beam intensity of the accelerator and the time change of the integrated dose value of the dose monitor are the same as those in the method of FIG. The beam intensity is controlled so as to be constant based on the command value. However, since there is a response delay, the irradiation amount per hour is reduced at the beginning of the irradiation of the spot 1, and the surplus after the irradiation of the spot 3 is completed. Irradiation can occur. A spot where the irradiation amount per hour in the spot 1 is small is managed by the integrated dose to the spot 1, so that there is no problem that the dose to the spot 1 decreases. However, since the dose after the spot 3 occurs after the integration of the accumulated dose to the spot 3 is finished, there is a possibility that the uniformity of the actual dose distribution is lowered.

  In the present embodiment, the time t1 'from the time t1 when the dose at the spot 1 expires to the start of changing the scanning electromagnet current value in order to start moving to the next spot is delayed by a certain finite value. In FIG. 7, the movement start time from spot 1 to spot 2 after the dose expiration of spot 1 is delayed by Δt1. Further, the movement start time from the spot 2 to 3 is delayed by Δt2. This finite time delay is assumed to be smaller than the irradiation time ΔT of the excessive dose at the final spot. In FIG. 7, when the beam intensity is I, the irradiation amount of the spot 1 increases by I × Δt1, and the irradiation amount of the spot 2 increases by I × (Δt2−Δt1). The irradiation amount of spot 3, which is the final spot, is reduced by I × Δt2.

  This embodiment can be executed by the overall controller of the particle beam therapy system. During the irradiation based on the treatment plan received from the treatment planning device, the irradiation control is performed so as to delay by Δt specified in advance after detecting the expiration signal when commanding the current value of the scanning magnet. As another method, Δt may be set in advance for the treatment planning apparatus, or the treatment planning apparatus may set an incentive value based on the number of spots, the position of an important organ, beam intensity, and the like. . In that case, the treatment plan is set so as to move between irradiation spots with a shift of Δt.

  In this way, in all irradiation spots that are scanned with a single stroke scanning path in the layer that is irradiated with the same energy, the final dose of the final spot is reduced by delaying the start time of movement from the expiration of the dose to the next spot. It becomes possible to distribute to places other than spots.

  As a method for suppressing a decrease in dose uniformity at the final spot other than the present embodiment, for example, in Patent Document 1, the scanning electromagnet is scanned at a high speed within a certain range at the final spot, thereby deteriorating the dose distribution due to the delayed dose. A method of dilution is disclosed. However, this method requires a finite range to dilute, and there is a problem that a delayed dose is applied to a region off the spot, that is, a region other than the affected part. In this embodiment, since the excess dose of the final spot can be distributed to each spot to be irradiated with one stroke, it is possible to reduce the dose application to the area other than the irradiation spot determined in the treatment plan. As described above, according to the present embodiment, in the scanning irradiation by the continuous beam, it becomes possible to disperse the excessive dose at the final spot, which has been generated in the past, to all the irradiation spots irradiated with one stroke with the same energy. Thus, it is possible to alleviate the deterioration of the dose distribution than in the past.

  Since the method according to the present embodiment can be implemented by additionally performing on the overall control apparatus side of the particle beam therapy system without changing the treatment plan, the processing load on the repair or treatment planning apparatus side can be reduced.

  The description overlapping with the above embodiment will be omitted.

  The particle beam therapy system of the present embodiment controls the time delay Δt from the expiration of the dose to the start of scanning so that it becomes a constant value at all spots. Thereby, it becomes possible to disperse the excessive dose in two places, the first spot and the last spot irradiated with one stroke.

  In this embodiment, by using a constant delay Δt, the control can be simplified, the irradiation accuracy is improved as a whole, and this embodiment is not applied to the dose distribution other than the first and last spots. The effect of reducing the influence of fluctuations from those set in the treatment plan can be obtained.

  The description overlapping with the above embodiment will be omitted.

  The particle beam therapy system according to the present embodiment controls the time delay from the expiration of the dose to the start of scanning so as to increase as the spot progresses. For example, Δt2 is made larger than Δt1 in FIG. As a result, in Example 2, the excess dose was dispersed in two places, the first spot and the last spot. However, the excess dose can be evenly distributed to all spots irradiated with one stroke. It becomes possible.

  This embodiment can further improve the irradiation accuracy.

5: Patient 10: Treatment planning device 11: Overall control device 12: Accelerator, beam transport system control device 13: Irradiation nozzle control device 20: Accelerator 21: Injector 22: Deflection electromagnet 30: High energy beam transport system 31: Deflection electromagnet 40: irradiation nozzles 41A, 41B: scanning electromagnet 42: dose monitor 43: position monitor 44: ridge filter 45: range shifter 50: treatment bed 51: affected area 52: layer 53 irradiation spot 61A, 61B of the affected area irradiated with the same energy Electromagnet power supply 71: Scanning electromagnet power supply controller 81: Bragg curve 82: Expanded Bragg peak (SOBP)
90: charged particle beam

Claims (9)

An accelerator to accelerate the charged particle beam;
An irradiation nozzle for irradiating the accelerated charged particle beam;
A control device for controlling the accelerator and the irradiation nozzle;
The irradiation nozzle is
A scanning electromagnet that scans a plurality of spots set to be irradiated with the charged particle beam;
A dose monitor for measuring the dose of the charged particle beam,
The particle beam therapy system according to claim 1, wherein the control device controls the current command value of the scanning electromagnet to be changed after a predetermined time has elapsed after detecting a spot dose expiration signal from the dose monitor. The particle beam therapy system according to claim 1,
The particle beam therapy system characterized in that the predetermined time is the same for all spots in the same layer. The particle beam therapy system according to claim 1,
The particle beam therapy system characterized in that the predetermined time is different in any two spots of the same layer. The particle beam therapy system according to claim 1,
The control device, when performing irradiation control based on a treatment plan received from a treatment plan device, additionally performs a control to start changing the current value of the scanning electromagnet after the predetermined time has elapsed. Particle beam therapy system. The particle beam therapy system according to claim 1,
A treatment planning device,
A particle beam treatment system, wherein a treatment plan is created in advance so that the predetermined time elapses in the treatment planning apparatus. While scanning the charged particle beam accelerated by the accelerator with a scanning electromagnet, scanning irradiation is performed with a continuous beam that does not turn the beam on and off for each spot. The irradiation amount at the spot is measured by a dose monitor, and predetermined irradiation is performed at the spot. A particle beam therapy system for irradiating the scanning electromagnet to the next spot after reaching a quantity,
A particle beam therapy system characterized in that the time from the arrival of a predetermined dose at each spot to the start of scanning of the next spot can be adjusted for each spot. The particle beam therapy system according to claim 6, wherein
After reaching a predetermined irradiation amount at each spot, the time from the start of scanning to the next spot is set to a constant value for all spots irradiated with a single stroke without turning off the beam. Particle beam therapy system. The particle beam therapy system according to claim 6, wherein
The time until the start of scanning to the next spot after reaching the predetermined irradiation amount at each spot is set so that it gradually increases in a series of spots irradiated with a single stroke without turning off the beam. A particle beam therapy system. The particle beam therapy system according to claim 6, wherein
A particle beam therapy system characterized by having a control device capable of adjusting the time from the start of scanning to the next spot after reaching a predetermined dose at each spot.

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