Particle beam therapy system, irradiation control device, and irradiation control method

Abstract

The present disclosure relates to a particle beam therapy system, an irradiation control device, and an irradiation control method. Provided is a particle beam therapy system capable of more accurately controlling a dose of a particle beam irradiated to a subject. A dose monitor (202) measures a dose of a beam (160). A position monitor (203) measures a beam size of the beam (160). An irradiation control device (108) calculates a measurement characteristic of the dose monitor (202) from the dose of the beam (160) and the beam size, and controls irradiation of the beam (160) to a patient (150) from the measurement characteristic and the dose.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a particle beam therapy system, an irradiation control device, and an irradiation control method. BACKGROUND

[0002] In recent years, particle beam therapy, which irradiates a patient's tumor with a particle beam such as a proton beam and a carbon beam, has attracted attention. In particle beam therapy, by using a phenomenon called a Bragg peak, which imparts a large dose to the periphery before the particle beam stops, a dose distribution that matches the shape of a tumor can be easily formed compared to X-ray therapy and the like, and thus highly accurate radiation therapy is expected to be realized.

[0003] In particle beam therapy, a charged particle beam (hereinafter, simply referred to as a particle beam) accelerated by an accelerator system having a linear accelerator or a synchrotron or the like is delivered to an irradiation nozzle as a particle beam, and is irradiated toward a tumor in a patient's body. As a main beam irradiation method, a passive method and a scanning method are cited. The passive method is a method in which the shape of a particle beam is matched to the shape of a tumor by expanding the beam diameter using a scatterer, a ridge filter, a collimator, or a patient port. The scanning method is a method in which a fine particle beam called a pencil beam is irradiated in a direction adjusted by a scanning electromagnet called an irradiation nozzle, and a plurality of minute regions (hereinafter, referred to as spots) virtually set in a tumor are sequentially irradiated, thereby irradiating a particle beam to the entire tumor. In addition, in the scanning method, there are a spot scanning method in which movement between spots is performed in a state where a particle beam is stopped, and a raster scanning method in which movement between spots is performed in a state where a particle beam is irradiated, and the like. In recent years, facilities that adopt the scanning method are increasing because they can cope with complex tumor shapes and changes therein.

[0004] In the scanning method, a particle beam is monitored using a position monitor and a dose monitor provided in the irradiation nozzle, and the irradiation dose is controlled on a spot-by-spot basis in accordance with the monitoring results. The position monitor measures the center position and the size of the particle beam, and the dose monitor measures the magnitude of the dose. An irradiation control device calculates the cumulative value of the irradiation dose, that is, the cumulative dose, irradiated to a spot from these measured values, and shifts to the irradiation of a beam for the next spot when the cumulative dose reaches a target dose (hereinafter, referred to as a prescription) set in advance for the spot. Therefore, in order to impart a sufficient dose to a tumor and suppress damage to healthy tissues in the periphery, high measurement accuracy is required for the position monitor and the dose monitor.

[0005] However, in a dose monitor, the problem that the dose rate, which is the detected dose per unit time, affects the measurement accuracy is known. The ionization chamber of a general dose monitor is a container in which a gap of a plurality of electrodes is filled with a fluid such as a gas or a liquid, and when a particle beam is incident, the fluid is ionized on the trajectory thereof, and thus, cations and electrons are generated. By applying a voltage between the electrodes, the cations and the electrons move to the opposite electrodes, respectively, and thus, a current flows between the electrodes for only a short time. The dose is calculated by measuring the current. However, as the dose rate increases, the density of the generated cations becomes large, and thus, the proportion of the cations and the electrons that recombine before reaching the electrodes increases, and the collection efficiency of the cations and the electrons collected in the dose monitor decreases.

[0006] In the past particle therapy, the dose rate was relatively small, and thus, the decrease in the collection efficiency of the dose monitor was about 1%, and the influence on the linearity of the dose monitor was small. However, in recent years, radiation therapy at an ultra-high dose rate, which is called FLASH radiation therapy, has attracted attention, and the demand for irradiation at a high dose rate has increased compared to the past. At a high dose rate, the collection efficiency of the ionization chamber sometimes decreases by about 10%, and in this case, the linearity of the dose monitor fails. Therefore, in order to accurately control the dose imparted to a subject, it is required to grasp the collection efficiency of the dose monitor.

[0007] In Patent Literature 1, a technique of correcting the collection efficiency of the ionization chamber according to a prescription sheet prepared in advance is disclosed. In this technique, according to the prescription sheet, the dose rate and the size of the beam irradiated to the patient at the time of treatment are estimated as beam parameters. According to the beam parameters, a correction coefficient that corrects the collection efficiency set in advance is determined for each point.

[0008] Prior Art Documents

[0009] Patent Literature 1: Japanese Patent No. 6807125 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] However, the beam parameters vary in the irradiation of the particle beam, and thus, the beam parameters estimated from the prescription sheet do not necessarily coincide with the beam parameters of the actually irradiated particle beam. In particular, in particle beam irradiation at a high dose rate, the variation in the beam parameters is large to an extent that cannot be ignored. Therefore, in the technique described in Patent Literature 1, the collection efficiency of the dose monitor cannot be properly corrected, and it is difficult to accurately control the dose of the particle beam irradiated to the subject.

[0012] The present disclosure was made in view of the above circumstances, and aims to provide a particle therapy system, an irradiation control device, and an irradiation control method that can more accurately control the dose of a particle beam irradiated to a subject.

[0013] Means for solving the problem

[0014] A particle beam therapy system according to an aspect of the present disclosure irradiates a particle beam to a subject, wherein the particle beam therapy system has a dose monitor that measures a dose of the particle beam, a position monitor that measures a beam size of the particle beam, and an irradiation control device that calculates a measurement characteristic corrected for a measurement characteristic of the dose monitor based on the dose and the beam size, and controls irradiation of the particle beam to the subject based on the measurement characteristic and the dose.

[0015] Effects of the invention

[0016] According to the present disclosure, the dose of the particle beam irradiated to the subject can be controlled more accurately. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a diagram showing the overall structure of a particle beam therapy system of Embodiment 1 of the present disclosure.

[0018] Figure 2 is a diagram showing the structure of an irradiation nozzle of Embodiment 1 of the present disclosure.

[0019] Figure 3 is a diagram showing an example of the structure of a dose monitor of Embodiment 1 of the present disclosure.

[0020] Figure 4 is a diagram showing an example of the structure of a position monitor of Embodiment 1 of the present disclosure.

[0021] Figure 5 is a diagram for explaining an example of a calculation method of the center position and size of the beam of Embodiment 1 of the present disclosure.

[0022] Figure 6 is a flowchart for explaining the operation of the particle beam therapy of Embodiment 1 of the present disclosure.

[0023] Figure 7 is a diagram showing an example of the structure of an irradiation control system of Embodiment 1 of the present disclosure.

[0024] Figure 8 is a flowchart for explaining an example of a monitoring process of Embodiment 1 of the present disclosure.

[0025] Figure 9 is a conceptual diagram of a collection efficiency table of Embodiment 1 of the present disclosure.

[0026] Figure 10 is a diagram showing an example of a determination method of a first point of Embodiment 2 of the present disclosure.

[0027] Figure 11 is a diagram showing the structure of the irradiation control system of Embodiment 2 of the present disclosure.

[0028] Figure 12 is a flowchart for explaining an example of the monitoring process of Embodiment 2 of the present disclosure.

[0029] Explanation of Reference Signs

[0030] 100: particle therapy system, 101: accelerator system, 102: beam transport system, 103: irradiation nozzle, 104: treatment table, 105: treatment planning device, 106: overall control device, 107: accelerator and beam transport system control device, 108: irradiation control device, 111: ion source, 112: injector, 113: synchrotron, 121: beam path, 122: deflection electromagnet, 200: irradiation system, 201A, 201B: scanning electromagnet, 202: dose monitor, 203: position monitor, 204: ridge filter, 205: range shifter, 206: dose monitor control device, 207: position monitor control device, 208: scanning electromagnet control device DETAILED DESCRIPTION

[0031] Hereinafter, Embodiments of the present disclosure will be explained with reference to the drawings.

[0032] [Embodiment 1]

[0033] First, the particle therapy system of Embodiment 1 of the present disclosure will be explained. Figures 1-9

[0034] Figure 1 is a diagram showing the overall structure of the particle therapy system of the present embodiment. Figure 1 The particle therapy system 100 shown is a system that irradiates a particle beam, i.e., a beam 160, to a patient 150 who is a subject. In the present embodiment, the particle therapy system 100 uses a spot scanning method or a raster scanning method that sequentially irradiates a plurality of minute regions, i.e., spots, virtually set in the body of the patient 150 respectively.

[0035] As shown in Figure 1 , the particle therapy system 100 has an accelerator system 101, a beam transport system 102, an irradiation nozzle 103, a treatment table 104, a treatment planning device 105, an overall control device 106, an accelerator and beam transport system control device 107, and an irradiation control device 108.

[0036] The accelerator system 101 is a device group that generates and emits the beam 160. In the present embodiment, the accelerator system 101 has an ion source 111, an injector 112, and a synchrotron 113. Figure 1 ​In the example shown in FIG. 1, the accelerator system 101 has an ion source 111, an injector 112, and a synchrotron 113. The ion source 111 generates charged particles that are the basis of the beam 160. The injector 112 injects the charged particles generated by the ion source 111 into the synchrotron 113. The synchrotron 113 accelerates the charged particles injected from the injector 112, generates, and outputs the beam 160.

[0037] Further, Figure 1 The accelerator system 101 shown in FIG. 1 is merely an example and is not limited to this example. For example, the accelerator system 101 can also be a device group in which a cyclotron or a synchrocyclotron, or the like, is used instead of the synchrotron 113.

[0038] The beam transport system 102 is a device group that transports the beam 160 emitted from the accelerator system 101 to the irradiation nozzle 103. The beam transport system 102 has a beam path 121 and a deflection electromagnet 122. The beam path 121 is a path through which the beam 160 passes, connecting the accelerator system 101 and the irradiation nozzle 103. The beam path 121 is in a vacuum state. The deflection electromagnet 122 deflects the beam passing through the beam path 121 by a magnetic field and transports it to the irradiation nozzle 103. The beam transport system 102 can or can not have a rotating gantry that adjusts the irradiation angle of the beam 160 toward the patient 150.

[0039] The irradiation nozzle 103 is a device housing having a device group that includes a device for irradiating the beam 160 transported from the beam transport system 102 toward the patient 150 and a device for measuring a parameter related to the beam 160, that is, a beam parameter. The more detailed structure of the irradiation nozzle 103 is described using FIG. 2. Figure 2 This will be described later.

[0040] The treatment table 104 is a bed on which the patient 150 is placed. The treatment table 104 moves according to the instruction from the overall control device 106, thereby moving the position and posture (angle) of the patient 150 to a desired position and posture. The treatment table 104 can, for example, achieve movement in 6-axis directions including translational movement along 3 axes respectively oriented in mutually different directions and rotational movement around the 3 axes respectively as rotational axes.

[0041] The treatment planning device 105 formulates a treatment plan for the patient 150 and creates a prescription sheet, which is sent to the overall control device 106. The prescription sheet shows, for each point of the beam 160, a target value of the dose of the beam 160 irradiated to the point, that is, a target dose.

[0042] The overall control device 106 is connected to the treatment table 104, the treatment planning device 105, the accelerator and beam transport system control device 107, and the irradiation control device 108, and controls the respective devices connected thereto in accordance with a prescription sheet from the treatment planning device 105.

[0043] The accelerator and beam transport system control device 107 controls the accelerator system 101 and the beam transport system 102 in accordance with an instruction from the overall control device 106.

[0044] The irradiation control device 108 controls the irradiation nozzle 103 in accordance with an instruction from the overall control device 106. In addition, the irradiation control device 108 processes a measurement result of the irradiation nozzle 103 and transmits it to the overall control device 106. A more detailed structure of the irradiation control device 108 will be described later. Figure 6

[0045] The treatment planning device 105, the overall control device 106, the accelerator and beam transport system control device 107, and the irradiation control device 108 are realized, for example, by a computer system having a central processing unit (CPU), a memory, a storage device, a communication interface device, a user interface (UI) device, and the like. These devices perform various processes, for example, by reading and executing a program recorded in the memory by the CPU. The program of each device can be single, can be divided into a plurality of programs, or can be a combination thereof. In addition, a part or all of the program of each device can be realized by a dedicated hardware or can be modularized. In addition, a part or all of the program can be installed in each device using a program distribution server or an external storage medium, and the like, which are not illustrated. In addition, each device can be constituted by independent devices, can be connected to each other through a wired or wireless network, or can be integrated with two or more devices.

[0046] Figure 2 is a diagram showing a structure example of the irradiation nozzle 103.

[0047] Figure 2 The irradiation nozzle 103 shown in the drawing has an irradiation system 200 for irradiating a beam 160 to a patient 150, a dose monitor control device 206, a position monitor control device 207, and a scanning electromagnet control device 208 as a control system for controlling the irradiation system 200. The irradiation system 200 has scanning electromagnets 201A and 201B, a dose monitor 202, and a position monitor 203.

[0048] In addition, the irradiation system 200 can have a ridge filter 204 for expanding a black peak of the beam 160 in a traveling direction of the beam 160, and a range shifter 205 for adjusting a depth to which the beam 160 reaches, as needed.

[0049] ​The scanning electromagnets 201A and 201B are scanning systems that scan the beam 160 in a plane (2-dimensional direction) orthogonal to the passing direction of the beam 160. The beam 160 scanned by the scanning electromagnets 201A and 201B is irradiated to a target volume 151 in the patient 150. The target volume 151 is an irradiation region of the beam 160, and, for example, in a case where the particle beam therapy system 100 treats a tumor such as a cancer of the patient 150, becomes a region in which a tumor region in which the tumor exists is added with a margin (blank region in which an error in the irradiation position is taken into account). A point irradiated by the beam 160 is set within the target volume 151.

[0050] The dose monitor 202 is a monitor for measuring the dose rate of the beam 160 irradiated to each point. The dose monitor 202 outputs a detection signal indicating the measurement result to the dose monitor control device 206. The dose monitor control device 206 calculates the dose rate of the beam 160 irradiated to each point from the detection signal from the dose monitor 202 and outputs to the irradiation control device 108.

[0051] Figure 3 FIG. 1 is a view showing an example of the dose monitor 202. Figure 3 The dose monitor 202 shown in the drawing is a parallel-plate type ionization chamber generally used.

[0052] As the dose monitor 202, a parallel-plate type ionization chamber shown in FIG. 2 is used. Figure 3 The dose monitor 202 of the parallel-plate type ionization chamber shown in the drawing is covered with a shielding wall 301, and a plurality of beam windows 302 having high transmissivity for the beam 160 are formed in the shielding wall 301. Specifically, the beam windows 302 are formed at positions opposite to each other of the shielding wall 301 in a manner that the beam 160 intruding from one beam window 302 is emitted from the other beam window. Further, in a space surrounded by the shielding wall 301, one or more high-voltage electrodes 303 and one or more plate-shaped collecting electrodes 304 are arranged in parallel. In the example shown in FIG. 2, the dose monitor 202 has one high-voltage electrode 303 and two collecting electrodes 304 arranged to sandwich the high-voltage electrode 303. A high voltage is applied to the high-voltage electrode 303, and an electric field is generated between the high-voltage electrode 303 and the collecting electrodes 304. Further, the space between the electrodes 303 and 304 is filled with a gas. Figure 3

[0053] The beam 160 intruding into the dose monitor 202 through the beam window 302 ionizes the gas between the electrodes 303 and 304 to generate cations and electrons. The generated cations and electrons move toward the collecting electrodes 304 due to the electric field generated between the electrodes 303 and 304. Due to the movement of the cations and electrons, an electric current 305 flows between the electrodes 303 and 304, which is measured by the dose monitor control device 206.

[0054] ​The dose of the beam 160 is proportional to the amount of ions generated. Therefore, the dose monitor control device 206 calculates the dose rate of the beam 160 from the current 305 by multiplying the value of the current 305 by an appropriate coefficient. Further, the dose rate calculated by the dose monitor control device 206 is a dose rate before correction, which does not take into account variations in the collection efficiency of the dose monitor 202.

[0055] Further, the dose monitor 202 is not limited to Figure 3 the example shown. For example, each of the electrodes 303 to 304 can be filled with a liquid or can be open to the air. In addition, the shape of each of the electrodes 303 to 304 is not limited to a flat plate shape, and can be, for example, a coaxial cylindrical shape or the like. Further, the dose monitor 202 is not limited to an ionization chamber, but can be any monitor in which the characteristics vary depending on the dose rate and the beam size.

[0056] Returning to Figure 2 the description of the dose monitor 202. The position monitor 203 is a monitor for measuring the center position of the beam 160 and the beam size. The position monitor 203 outputs a detection signal indicating the measurement result to the position monitor control device 207. The position monitor control device 207 calculates the center position of each beam and the beam size from the detection signal input from the position monitor 203 and outputs the same to the irradiation control device 108.

[0057] Figure 4 is a view showing an example of the position monitor 203. Figure 4 The position monitor 203 shown in

[0058] The multi-strip ionization chamber as the position monitor 203 is covered with a shielding wall (not shown) as with the dose monitor 202 shown in Figure 3 and a plurality of beam windows 401 having high transmittance with respect to the beam 160 are formed in the shielding wall. Specifically, the beam windows 402 are formed at positions opposite to each other in the shielding wall in such a manner that the beam 160 intruding from one beam window 402 is emitted from the other beam window. In addition, one or more high-voltage electrodes 402 in the form of a flat plate are arranged in parallel with one or more collectors 403A and 403B in the form of a flat plate in a space surrounded by the shielding wall. A high voltage is applied to the high-voltage electrodes 402, and an electric field is generated between the high-voltage electrodes 402 and the collectors 403A and 403B. In addition, each of the electrodes 402, 403A, and 403B is filled with a fluid such as a gas or a liquid.

[0059] The collector 403A is composed of a plurality of long, thin collectors arranged in parallel in one direction (referred to as the X direction) in the plane, and the collector 403B is composed of a plurality of long, thin collectors arranged in parallel in a direction (referred to as the Y direction) orthogonal to the X direction in the plane.

[0060] The beam 160 intruding into the position monitor 203 through the beam window 401 ionizes the fluid between the electrodes 402 to 403 to generate cations and electrons. The generated cations and electrons move toward each of the small electrodes of the collector 304A or 304B due to the electric field generated between the electrodes 402 to 403, and an electric current 404 is generated due to the movement of the cations and electrons, which is measured by the position monitor control device 207 for each of the small electrodes. Thus, the position monitor control device 207 can measure the 2-dimensional distribution of the generated ions and the dose distribution in the in-plane direction of the collector 304A or 304B from the electric current 404 for each of the small electrodes, and can calculate the center position and the beam size of the beam 160 from the dose distribution.

[0061] Figure 5 is a diagram for explaining an example of a calculation method of the center position and the beam size of the beam 160. In Figure 5 , the horizontal axis indicates the center position in the X direction of each of the small electrodes of the collector 403A, and the vertical axis indicates the current value. In addition, Figure 5 each of the data points 501 indicates the current value indicated by the detection signal of each of the small electrodes.

[0062] If it is assumed that the shape of the beam 160 follows a Gaussian distribution, the peak position 503 and the standard deviation 504 when the distribution of the data points 501 is approximated by a Gaussian function 502 become the center position and the beam size of the beam 160, respectively. In addition, in Figure 5 , an example of a 1-dimensional distribution is shown for simplicity, but actually, a 2-dimensional dose distribution is approximated by a 2-dimensional Gaussian function.

[0063] In addition, the calculation method of the center position and the beam size of the beam 160 is not limited to the example described above, and it can be assumed that the shape of the beam 160 follows a Lorentz distribution, and the dose distribution is approximated by a Lorentz function. In addition, the position monitor 203 is not limited to the example shown in Figure 3 . For example, the position monitor 203 can be a multi-strip ionization chamber or the like.

[0064] Returning to the explanation of Figure 2 , the irradiation control device 108 calculates the irradiation position of the beam 160 from the center position of the beam 160 calculated by the position monitor control device 207. In addition, the irradiation control device 108 calculates the collection efficiency as the measurement characteristic of the dose monitor 202 from the beam parameters (dose rate, center position, and beam size) transmitted from the dose monitor control device 206 and the position monitor control device 207. The irradiation control device 108 corrects the dose rate calculated by the dose monitor control device 206 from the collection efficiency, and thus, calculates the corrected dose rate taking into account the variation of the collection efficiency.

[0065] Next, the operation of the particle therapy system 100 will be described.

[0066] Figure 6 is a flowchart for describing an example of a treatment process for treating the patient 150 with the particle therapy system 100.

[0067] In the particle therapy, generally, a high dose of the beam 160 is given to the patient 150 at a time, and thus, in order to suppress damage to normal tissues of the patient 150, fractionated irradiation of the beam to the patient 150 is performed. In the present embodiment, the fractionation unit is one day, and the fractionation number is 30. However, the fractionation unit and the fractionation number are not limited to these examples. For example, the fractionation unit need not be one day, and a plurality of treatments can be performed in one day.

[0068] First, at the start of the treatment on the day (supposed to be the d-th day) (step S601), the treatment planning device 105 creates a prescription sheet as a treatment plan (step S602). The initial value of d is 1.

[0069] In step S602, specifically, the treatment planning device 105 first reads in an in-vivo image that visualizes the affected part of the patient 150, that is, the periphery of a tumor, and converts a distribution of thickness from the body surface of the patient 150 to the affected part to a distribution of water equivalent thickness ratio from the in-vivo image. The in-vivo image is created, for example, by CT (Computed Tomography) examination or the like. The water equivalent thickness ratio is the ratio of the thickness of water that causes the same energy loss to the thickness of the local medium with respect to the beam 160, and is a physical quantity that determines the stopping distance of the beam 160.

[0070] Next, the treatment planning device 105 determines the profile of the 3-dimensional irradiation region of the beam 160, that is, the target volume 151, using the in-vivo image. For example, the treatment planning device 105 displays the in-vivo image to allow an operator such as a doctor to delineate the profile of the tumor, and determines the profile of the target volume 151 by giving a predetermined margin to the profile of the tumor.

[0071] Further, the treatment planning device 105 creates a prescription sheet (point-by-point set target dose). Specifically, the treatment planning device 105 first sets a target dose for the target volume 151. The target dose is input, for example, by the operator. The treatment planning device 105 calculates the position of the point for giving the target dose to the target volume 151 and the target dose using a prescribed optimization calculation method or the like in accordance with the distribution of the water equivalent thickness ratio, and thereby creates the prescription sheet. The treatment planning device 105 displays the prescription sheet, and when the operator acknowledges the prescription sheet, transmits the prescription sheet to the overall control device 106.

[0072] The overall control device 106 generates control instruction data for controlling the accelerator and beam transport system control device 107 and the irradiation control device 108 in accordance with the prescription sheet from the treatment planning device 105 in a spot-by-spot manner, and transmits the data to the accelerator and beam transport system control device 107 and the irradiation control device 108. The transmitted data is stored in a memory (not shown) in the accelerator and beam transport system control device 107 and the irradiation control device 108. In the control instruction data for the accelerator and beam transport system control device 107, for example, the exciting current values of the respective electromagnets of the accelerator system 101 and the beam transport system 102 and the high-frequency power value applied to the high-frequency accelerating cavity, which are determined in accordance with the beam energy corresponding to the depth of the spot position, and the like are included. In addition, in the control instruction data for the irradiation control device 108, the target dose, the current values of the scanning electromagnets 201A and 201B, and the like are included.

[0073] The processing of step S602 ends above. Further, in a case where the prescription sheet is not approved by the operator, the target dose is re-set.

[0074] After that, the patient 150 is placed on the treatment table 104, and the alignment of the patient 150 is performed in a manner that matches the time of the photographing of the in-vivo image, and the operator instructs the irradiation of the beam 160 to the particle therapy system 100 (step S603).

[0075] Then, the overall control device 106 transmits an irradiation start instruction for the spot (set as the nth spot) to be irradiated to the accelerator and beam transport system control device 107 and the irradiation control device 108 (step S604). The initial value of n is 1.

[0076] The accelerator and beam transport system control device 107 starts the acceleration of the beam 160 in accordance with the control instruction data stored in the memory if the irradiation start instruction is received. The irradiation control device 108 changes the current values of the scanning electromagnets 201A and 201B via the scanning electromagnet control device 208 if the acceleration of the beam 160 is completed. The accelerator and beam transport system control device 107 emits the beam 160 if the change of the current values is completed. The emitted beam 160 is irradiated to the target volume 151 of the patient 150 through the beam transport system 102 and the irradiation nozzle 103. The dose monitor 202 and the position monitor 203 measure the beam parameters of the beam 160, and the irradiation control device 108 calculates the dose of the beam 160 for the nth spot in accordance with the beam parameters (step S605).

[0077] Subsequently, when the dose reaches the target dose, the irradiation control device 108 sends an end signal to the overall control device 106 indicating that the irradiation of the beam 160 to the nth point has ended. Upon receiving the end signal, the overall control device 106 executes the process of ending the irradiation of the beam 160 to the nth point, i.e., the end process (step S606). The end process, when using the point scanning method, is the process of stopping the irradiation of the beam 160; when using the raster scanning method, it is the process of transitioning to the irradiation preparation for the next point. The point scanning method involves moving between points while the beam is stopped, while the raster scanning method involves moving between points while the beam has been irradiated.

[0078] Then, the overall control device 106 determines whether the irradiation of the beam 160 toward the last point has ended (step S607).

[0079] If the irradiation of the last point by the beam 160 has not ended, the overall control device 106 increments n and instructs the accelerator and beam delivery system control device 107 and the irradiation control device 108 to prepare for irradiation of the next point (step S608), and returns to the processing of step S604.

[0080] On the other hand, if the irradiation of the final point by the beam 160 ends, the treatment for the day ends. Then, the overall control device 106 determines whether it is the final day. If it is not the final day, the process in step S601 is executed; if it is the final day, the process ends.

[0081] In addition, the irradiation control device 108 can also be directly connected to the accelerator and beam delivery system control device 107, and send various signals directly to the accelerator and beam delivery system control device 107.

[0082] The following is about Figure 6 The steps S604 to S606, namely the monitoring of the radiation dose, will be explained in more detail.

[0083] Figure 7 This is a diagram illustrating a structural example of an irradiation control system that includes an irradiation nozzle 103 and an irradiation control device 108. Figure 8 It is used for Figure 7 The flowchart illustrates an example of the monitoring and processing of the irradiation control system shown. The following explanation uses the irradiation of the beam 160 at the nth point as an example.

[0084] like Figure 7As shown, the dose monitor control device 206 has an I / F converter 702 that converts the current output from the dose monitor 202 into a pulse signal, and a CPU 705 that calculates the dose rate from the pulse signal converted by the I / F converter 702. Further, the pulse frequency of the pulse signal indicates the dose rate. The position monitor control device 207 has an I / F converter 704 that converts the current output from the position monitor 203 into a pulse signal, and a CPU 706 that calculates the center position and the beam size of the beam 160 from the pulse signal converted by the I / F converter 704.

[0085] Further, the irradiation control device has a memory 701 that stores the control instruction data (target dose of each point) and a CPU 707. Further, the CPU 707 has a counter 703 that counts the number of pulses.

[0086] When the step S604 is started, the overall control device 106 first sends an irradiation start instruction to the accelerator and beam transport system control device 107 and the irradiation control device 108 (step S801). The accelerator and beam transport system control device 107, upon receiving the irradiation start instruction, accelerates and emits the beam 160 in accordance with the control instruction data stored in the memory (step S803).

[0087] The CPU 707 of the irradiation control device 108 reads the target dose corresponding to the nth point among the target doses stored in the memory 701 in the step S602 during the period from the reception of the irradiation start instruction to the emission of the beam 160 by the accelerator and beam transport system control device 107 (between steps S801 and S803). In the present embodiment, the I / F converter 702 of the dose monitor control device 206 converts the current output from the dose monitor 202 into a pulse signal, and the number of pulses of the pulse signal indicates the dose, so the CPU 707 converts the target dose into a target number of pulses converted from the number of pulses and sets it in the counter 703 (step S802).

[0088] The conversion count for converting the target dose into the target number of pulses is determined in accordance with the characteristics of the dose measuring circuit including the dose monitor 202 and the I / F converter 702. Further, the processing of the step S802 can also be performed during the period from the end of the irradiation of the beam 160 against the previous point (the nth-1 point) to the sending of the irradiation start instruction against the point.

[0089] Then, when the beam 160 is emitted (step S803), the current detected by the dose monitor 202 and the position monitor 203 during the irradiation of the target volume 151 by the beam 160 is converted into pulse signals by the I / F converters 702 and 704 in the dose monitor control device 206 and the position monitor control device 207, respectively. The CPU 705 of the dose monitor control device 206, if using... Figure 3 As explained, the dose rate of beam 160 is calculated based on the pulse signal and sent to the irradiation control device 108. Additionally, the CPU 706 of the position monitoring control device 207, if using... Figure 4 As explained, the center position and beam size of the beam 160 are calculated based on the two-dimensional distribution of the pulse frequency of the pulse signal and sent to the irradiation control device 108 (step S804). Furthermore, the conversion factor for converting the current into a pulse signal, like the conversion factor for the target dose mentioned above, is a constant determined based on the characteristics of the dose measurement circuit.

[0090] The CPU 707 of the irradiation control device 108 calculates the collection efficiency of the dose monitor 202 for the beam 160 based on the dose rate and the beam size (step S805).

[0091] The following is an example of a theoretical calculation method for calculating collection efficiency.

[0092] If we assume that the beam spread of 160 follows a Gaussian distribution, the beam current density i(r) of 160 at a distance r from the center of 160 is described by the following Equation 1 using the actual cumulative beam current I and beam size σ of 160. Furthermore, the distance r is the distance in a direction orthogonal to the direction of travel of the beam 160.

[0093]

Mathematical Formula 1

[0094]

[0095] On the other hand, using the beam current density i(r) in a small region within the dose monitor 202 and the local collection efficiency f(r), the cumulative beam current J measured by the dose monitor 202 is expressed by the following formula 2.

[0096]

Mathematical Formula 2

[0097]

[0098] According to Boag's logic, the local collection efficiency f(r) and the beam current density i(r) have the relationship shown in Equation 3.

[0099]

Mathematical Expression 3

[0100]

[0101] Here, k is 2.01 x 10 7 [V / (m 0.5 A 0.5 )], V is an applied voltage applied to the dose monitor 202, and d is a constant determined by the configuration of the dose monitor 202, for example, the interval between the high-voltage electrode 303 and the collector electrode 304 in the case where the dose monitor 202 is configured of one high-voltage electrode 303 and one collector electrode 304. The collection efficiency F of the dose monitor 202 as a whole is represented by Equation 4 as a function of the cumulative beam current J by integrating Equation 1 and Equation 3 into Equation 2.

[0102] [Equation 4]

[0103]

[0104] The cumulative beam current J is calculated by applying a certain coefficient to the dose rate calculated by the dose monitor control device 206, and the beam size σ is calculated by the position monitor control device 207. Therefore, the CPU 707 of the irradiation control device 108 can calculate the collection efficiency F by substituting these values into Equation 4.

[0105] Further, the above-described method of calculating the collection efficiency is merely an example, and is not limited to this method. For example, assuming that the spread of the beam 160 follows a Gaussian distribution, but in the case where the spread of the beam 160 is a distribution defined in accordance with the cumulative beam current and the beam size, it is also possible to assume that the spread of the beam 160 follows a Lorentz distribution or the like.

[0106] In addition, for example, instead of the method of calculating the collection efficiency in accordance with Equation (4) as a logical expression, a method of using a collection efficiency table representing the relationship between the dose rate and the beam size σ and the collection efficiency can be used. In this method, the CPU 707 of the irradiation control device 108 calculates the collection efficiency by referring to the collection efficiency table prepared in advance.

[0107] Figure 9 is a graph showing an example of a collection efficiency table. Figure 9 The collection efficiency table 900 shown is a table in which the rows are dose rates and the columns are matrices corresponding to the beam sizes, and each element represents the dose rate corresponding to the own row and column and the collection efficiency corresponding to the beam size.

[0108] The method of preparing the collection efficiency table is exemplified by the following method: a beam whose dose rate and beam size are known is subjected to measurement based on the dose monitor 202, the ideal dose rate is compared with the measured dose rate, and thus the process of calculating the collection efficiency is repeatedly executed while changing the dose rate and the beam size.

[0109] Returning to Figure 7 and Figure 8 the explanation of the actions. When the process of step S805 ends, the CPU 707 of the irradiation control device 108 acquires a correction pulse frequency corresponding to a dose rate taking into account the variation in the collection efficiency, i.e., a correction dose rate, by multiplying the pulse frequency of the pulse signal from the dose monitor control device 206 by the inverse of the collection efficiency. The CPU 707 accumulates the correction pulse frequency using the counter 703, thereby counting the number of correction pulses corresponding to a correction dose obtained by correcting the measured dose, which is the dose imparted to the nth point measured by the dose monitor 202, with the collection efficiency.

[0110] The CPU 707 of the irradiation control device 108 determines whether the correction dose has reached the target dose by determining whether the number of correction pulses has reached the target number of pulses read from the memory 701 (step S807). In the case where the correction dose has not reached the target dose, the process of step S804 is executed again, and in the case where the correction dose has reached the target dose, the monitoring process of the irradiation dose ends, and the process of step S606 of Figure 6 is executed.

[0111] Next, the effects of the present embodiment will be described.

[0112] According to the present embodiment, the dose monitor 202 measures the dose of the beam 160. The position monitor 203 measures the beam size of the beam 160. The irradiation control device 108 calculates the measurement characteristic of the dose monitor 202 from the dose and the beam size of the beam 160, and controls the irradiation of the beam 160 to the patient 150 in accordance with the measurement characteristic and the dose. Therefore, the irradiation of the beam 160 to the patient 150 is controlled on the basis of the measurement characteristic of the dose monitor 202 calculated from the actually measured dose and beam size of the beam 160, and thus the dose of the beam 160 irradiated to the patient 150 can be controlled more accurately.

[0113] In addition, in the present embodiment, the irradiation control device 108 calculates a correction dose, which is the dose corrected with the measurement characteristic, and executes the process of ending the irradiation of the beam 160 in the case where the cumulative value of the correction dose reaches the target dose. Therefore, the setting of the target dose and the like can be performed as in the past only by the correction dose, and thus no change in the processing system is required, i.e., no addition and change of the existing hardware device are required, and the additional cost can be suppressed.

[0114] In addition, in the present embodiment, the collection efficiency of the ionization chamber is used as the measurement characteristic of the dose monitor 202. Therefore, a general dose monitor 202 can be used, and thus the additional cost can be suppressed.

[0115] [Example 2]

[0116] Next, the particle beam therapy system and the irradiation control device of Example 2 of the present disclosure will be described. Hereinafter, mainly the points different from Example 1 will be described. Further, the same reference numerals are attached to the structures common to Example 1. Figures 10-12

[0117] The overall structure of the particle beam therapy system 100 of Example 2 is the same as that of the particle beam therapy system 100 of Example 1 shown in FIG. 1. However, in the present example, the irradiation control device 108 calculates the corrected target dose that corrects the target dose in accordance with the collection efficiency of the dose monitor 202 instead of the correction dose. The irradiation control device 108 executes the end process of ending the irradiation of the beam 160 in a case where the cumulative value of the dose measured by the dose monitor 202 reaches the corrected target dose. The calculation of the corrected target dose is performed by point, and the collection efficiency used for the calculation of the corrected target dose of each point is calculated in accordance with the dose and the beam size of the beam 160 irradiated to the points in the irradiation sequence earlier than the point, i.e., the reference point. In the present example, the collection efficiency of each point is calculated in accordance with the dose and the beam size of the beam 160 irradiated to the point one earlier than the point in the irradiation sequence. Figure 1 In a case where the difference in the characteristics of the beam 160 with respect to each of the reference point and the irradiation point is small enough, the collection efficiency can be calculated with high accuracy in the present example, and the irradiation control with high accuracy can be performed. For example, in a case where the scale of the periodic variation of the beam parameters is larger than the irradiation time for one point, and the difference in the beam parameters between the adjacent points is smaller than the difference between the irradiation instruction and the actual irradiation, the collection efficiency can be calculated with higher accuracy than that calculated in accordance with the prescription by referring to the average value of the beam parameters of the previous point.

[0118] The overall flow of the treatment process of the treatment patient 150 in the present example is the same as that of the treatment process described using Example 1. However, for the first point at which the beam 160 is initially irradiated, the dose and the beam size of the beam 160 used for calculating the corrected target dose cannot be obtained, and therefore, the irradiation control device 108 executes the additional process for reducing the influence of the error of the dose imparted to the first point on the treatment quality at the time of the creation of the prescription in step S602.

[0119] Figure 6 The additional process is a process of deciding the point satisfying a prescribed condition as the first point from among the plurality of points divided from the target volume 151. For example, in the additional process, the first point is decided in accordance with the target volume 151.

[0120]

[0121] Figure 10 ​​​is an example of a first point. In Figure 10 In the example of FIG. 10, the first point is set as a point 1001 closest to the center of the target volume 151. In this case, since it is considered that there is no normal tissue or little normal tissue in the vicinity of the point 1001, it is possible to reduce the influence of the error of the dose on the treatment quality.

[0122] Further, Figure 10 The first point shown in FIG. 10 is only an example, and is not limited thereto. For example, the first point can be a point having a distance from a prescribed organ of a certain value or more, or the like. In addition, the first point set by an arbitrary method can be divided into a plurality of finer sub-points, and any one of the sub-points can be set as the first point again. In this case, it is possible to reduce the target dose for the sub-points, and thus it is possible to reduce the dose given to the sub-points, and as a result, it is possible to reduce the influence of the error of the dose on the treatment quality.

[0123] The additional processing can be automated by a program of the irradiation control device 108, or can be processing in which the operator selects by displaying the target volume 151 and each point, or the like.

[0124] Hereinafter, the monitoring processing of the irradiation dose in Embodiment 2 (the processing of Steps S604 to S606 of FIG. 6) will be described in more detail. Figure 6

[0125] Figure 11 is a diagram showing a configuration example of an irradiation control system including the irradiation nozzle 103 and the irradiation control device 108. Figure 12 is a flowchart for explaining an example of the monitoring processing of the irradiation control system shown in FIG. 10. Hereinafter, the irradiation of the beam 160 with respect to the nth point will be described as an example. Figure 11 After the irradiation of the nth point is started, the overall control device 106 transmits an irradiation start instruction to the accelerator and beam transport system control device 107 and the irradiation control device 108 (Step S1201). The accelerator and beam transport system control device 107, upon receiving the irradiation start instruction, accelerates and emits the beam 160 in accordance with the control instruction data stored in the memory (Step S1204).

[0126] The CPU 707 of the irradiation control device 108 executes the following Steps S1202 to S1203 during a period from when the irradiation start instruction is received to when the beam 160 is emitted by the accelerator and beam transport system control device 107.

[0127]

[0128] ​​First, the CPU 707 calculates the collection efficiency of the dose monitor 202 based on the average dose rate and the average size of the beam 160 irradiated to the first point (n-1th point) stored in the memory 701 (step S1202). The average dose rate is the average value of the dose rate of the beam 160 irradiated to the first point, and the average size is the average value of the beam size of the beam 160 irradiated to the first point. In addition, the average dose rate is the average value of the dose rate without correction based on the collection efficiency. The method of calculating the collection efficiency can be the method using the logical expression (4) as in Embodiment 1, or can be the method using the table as shown in FIG. 6. Figure 9

[0129] In addition, in the case of n = 1, that is, when the beam 160 is irradiated to the first point, there are no average dose rate and average size corresponding to the first point. Therefore, the CPU 707 can set a fixed value (for example, 1) as the collection efficiency, or can estimate the collection efficiency based on the average dose rate and the average size estimated from the prescription sheet.

[0130] Next, the CPU 707 reads the target dose of the n-th point from the memory 701, and calculates the corrected target dose by correcting the target dose based on the collection efficiency. The CPU 707 converts the corrected target dose into the corrected target pulse number converted into the number of pulses and sets it in the counter 703 (step S1203).

[0131] Then, when the beam 160 is emitted (step S1204), the electric current detected by the dose monitor 202 and the position monitor 203 in the irradiation of the beam 160 to the target volume 151 is respectively converted into a pulse signal by the I / F converters 702 and 704 in the dose monitor control device 206 and the position monitor control device 207 and output. The CPU 707 of the irradiation control device 108 transmits the pulse signal output from the I / F converter 702 to the counter 703, and accumulates the number of pulses. That is, in the present embodiment, unlike Embodiment 1, correction of the dose rate based on the collection efficiency is not performed. In addition, the CPU 706 of the position monitor control device 207 calculates the center position and the beam size of the beam 160 based on the pulse signal output from the I / F converter 702 (step S1205).

[0132] The CPU 707 of the irradiation control device 108 judges whether the accumulated number of pulses reaches the corrected target pulse number of the n-th point read from the memory 701, and thereby judges whether the dose given to the n-th point reaches the corrected target dose (step S1206).

[0133] ​In a case where the dose does not reach the corrected target dose, the process returns to step S1205. On the other hand, in a case where the dose reaches the corrected target dose, the CPU 705 of the dose monitor control device 206 calculates an average value of the dose rate of the beam 160 irradiated to the first point as a pre-correction average dose rate, and records it in the memory 701 of the irradiation control device 108. In addition, the CPU 706 of the position monitor control device 207 calculates an average value of the beam size of the beam 160 irradiated to the first point as an average size, and records it in the memory 701 of the irradiation control device 108 (step S1207), and the process ends. The pre-correction average dose rate and the average size are sometimes collectively referred to as average irradiation parameters. In addition, the pre-correction average dose rate is a name used for convenience, and in the present embodiment, correction of the dose rate is not performed.

[0134] In the above actions, the timing of calculating the average irradiation parameters and the collection efficiency is not limited to the timing of using the Figure 12 explanations. For example, the average irradiation parameters can be calculated from the number of pulses accumulated until a predetermined time point before the irradiation of the beam 160 ends, and the collection efficiency can be calculated during a period from the timing of the end of the irradiation of the beam 160 to the timing of the start of the irradiation to the next point.

[0135] In addition, in the above example, the reference point is the first point before the object point, but is not limited to this example. For example, the irradiation control device 108 can select a point closest to the beam 160 irradiated to the object point as the reference point, in accordance with the trend of the variation of the beam parameters of the beam 160.

[0136] Next, the effects of the present embodiment will be described.

[0137] As described above, according to the present embodiment, the irradiation control device 108 calculates a corrected target dose in which a target dose decided in advance is corrected, in accordance with the measurement characteristics, and in a case where the cumulative value of the dose reaches the corrected target dose, performs a process of ending the irradiation of the beam 160. Therefore, as in Embodiment 1, the target dose can be set as in the past, and thus, the change of the processing system is not required. Therefore, the addition and the change of the existing hardware devices are not required, and the additional cost can be suppressed.

[0138] In addition, in the present embodiment, the irradiation control device 108 calculates the corrected target dose for each point in accordance with the dose and the beam size of the beam 160 irradiated to a point earlier than the point. Therefore, the dose of the beam 160 does not need to be corrected in real time, and thus, a delay in the judgment of ending the irradiation of the beam 160 due to the processing time involved in the correction can be suppressed, and unnecessary irradiation can be suppressed.

[0139] Further, in the present embodiment, the irradiation control device 108 calculates the correction target dose for each point in accordance with the dose and the beam size of the beam 160 irradiating a point adjacent to the point. Therefore, the correction target dose can be calculated in accordance with the dose and the beam size of the beam 160 considered to be closest to the characteristics of the beam 160, and thus the dose of the beam 160 irradiated to the patient 150 can be controlled more accurately.

[0140] Further, in the present embodiment, the point satisfying the prescribed condition is set as the first point at which the beam 160 is initially irradiated. Therefore, the influence of the error in the amount of irradiation of the first point on the treatment quality can be reduced.

[0141] Further, the present disclosure is not limited to the above-described embodiments, and various modifications are included, for example, the above-described embodiments are described in detail in order to easily understand the present disclosure, and are not limited to necessarily having all the structures described. Further, a part of the structure of an embodiment can be replaced with the structure of another embodiment, and further, the structure of another embodiment can be added to the structure of an embodiment. Further, to a part of the structure of each embodiment, addition, deletion, or replacement of another structure can be performed.

Claims

1. A particle beam therapy system for irradiating a subject with a particle beam, characterized in that, The particle beam therapy system has the following features: A dose monitor that measures the dose of the particle beam; A position monitor that measures the beam size of the particle beam; An irradiation control device calculates the measurement characteristics of the dose monitor based on the dose and the beam size, and controls the irradiation of the particle beam onto the subject based on the measurement characteristics and the dose. The irradiation control device calculates a corrected dose based on the measurement characteristics, and if the cumulative value of the corrected dose reaches the target dose, it executes a process to terminate the irradiation of the particle beam, or... The irradiation control device calculates a corrected target dose based on the measurement characteristics, and performs a process to terminate the irradiation of the particle beam when the cumulative value of the dose reaches the corrected target dose.

2. The particle beam therapy system according to claim 1, characterized in that, The target dose is pre-set for each of the multiple tiny regions in the subject that will be irradiated by the particle beam. The irradiation control device performs the following process: sequentially irradiating the plurality of micro-regions with the particle beam, and terminating the irradiation of the micro-region with the particle beam when the corrected dose of the particle beam irradiating any one of the micro-regions reaches the target dose of that micro-region.

3. The particle beam therapy system according to claim 1, characterized in that, The target dose is pre-set for each of the multiple tiny regions in the subject that will be irradiated by the particle beam. The irradiation control device performs the following process: sequentially irradiating the plurality of micro-regions with the particle beam, and terminating the irradiation of the micro-region with the particle beam when the dose of the particle beam irradiating any one of the micro-regions reaches the correction target dose for that micro-region.

4. The particle beam therapy system according to claim 3, characterized in that, The irradiation control device calculates the corrected target dose for each micro-region based on the dose and the beam size of the particle beam irradiating a micro-region that precedes the micro-region in the irradiation sequence of the beam.

5. The particle beam therapy system according to claim 4, characterized in that, The irradiation control device calculates the corrected target dose for each micro-region based on the dose and the beam size of the particle beam irradiating the micro-region that precedes the micro-region in the irradiation sequence.

6. The particle beam therapy system according to claim 3, characterized in that, The irradiation control device determines the initial small area to be irradiated by the particle beam based on the irradiation area, i.e., the target volume, of the irradiated particle beam.

7. The particle beam therapy system according to claim 1, characterized in that, The dose monitor is an ionization chamber. The measured characteristic is the collection efficiency of the ionization chamber.

8. An irradiation control device connected to a dose monitor and a position monitor, the dose monitor measuring the dose of a particle beam irradiating a subject, the position monitor measuring the beam size of the particle beam, characterized in that, The measurement characteristics of the dose monitor are calculated based on the dose and the beam size. Based on the measurement characteristics and the dosage, the particle beam is controlled to irradiate the subject. A corrected dose is calculated based on the measured characteristics, and if the cumulative value of the corrected dose reaches the target dose, a process to terminate the irradiation of the particle beam is performed, or... Based on the measurement characteristics, a corrected target dose is calculated to correct for a predetermined target dose. If the cumulative value of the dose reaches the corrected target dose, a process to terminate the irradiation of the particle beam is performed.

9. An irradiation control method for a particle beam therapy system, characterized in that, Measure the dose of the particle beam. Measure the beam size of the particle beam. Based on the dose and the beam size, the measurement characteristics for measuring the dose are calculated. The irradiation of the particle beam is controlled based on the measured characteristics and the dose. A corrected dose is calculated based on the measured characteristics, and if the cumulative value of the corrected dose reaches the target dose, a process to terminate the irradiation of the particle beam is performed, or... Based on the measurement characteristics, a corrected target dose is calculated to correct for a predetermined target dose. If the cumulative value of the dose reaches the corrected target dose, a process to terminate the irradiation of the particle beam is performed.

Images