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

Abstract

To provide a particle beam therapy system that can more accurately control the dose of a particle beam with which a subject is irradiated.SOLUTION: A dose monitor 202 measures the dose of a beam 160. A position monitor 203 measures the beam size of the beam 160. An irradiation control device 108 calculates a measurement characteristic of the dose monitor 202 on the basis of the dose and the beam size of the beam 160, and controls the irradiation of a patient 150 with the beam 160 on the basis of the measurement characteristic and the dose.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, particle beam therapy, which irradiates tumors in patients with particle beams such as proton beams and carbon beams, has been attracting attention. In particle beam therapy, a phenomenon called the Black peak, in which a large dose is delivered to the surrounding area just before the particle beam stops, can be used to easily create a dose distribution that matches the shape of the tumor compared to X-ray therapy, etc., and is therefore expected to realize highly accurate radiation therapy.

[0003] In particle beam therapy, charged particle beams (hereinafter simply referred to as particle beams) accelerated by an accelerator system, such as a linear accelerator or synchrotron, are transported to an irradiation nozzle and irradiated toward a tumor inside the patient's body. Main beam irradiation techniques include passive and scanning. Passive irradiation involves expanding the beam diameter using a scatterer, ridge filter, collimator, or patient bolus to match the particle beam shape to the tumor's shape. Scanning involves adjusting the irradiation direction of a thin particle beam, called a pencil beam, using a scanning magnet in a container called an irradiation nozzle to sequentially irradiate multiple virtually defined microscopic regions (hereinafter referred to as spots) within the tumor, thereby irradiating the entire tumor with the particle beam. Scanning techniques include spot scanning, in which the particle beam is moved between spots while stationary, and raster scanning, in which the particle beam is moved between spots while irradiating. In recent years, an increasing number of facilities have adopted scanning techniques due to their ability to accommodate complex tumor shapes and their changes.

[0004] In the scanning method, a position monitor and a dose monitor installed in the irradiation nozzle monitor the particle beam, and the irradiation dose is controlled for each spot based on the monitoring results. The position monitor measures the center position and size of the particle beam, and the dose monitor measures the dose. The irradiation control device calculates the cumulative dose, which is the cumulative value of the irradiation dose irradiated to the spot, from these measurements. When the cumulative dose reaches a target dose (hereinafter referred to as a prescription) preset for each spot, the irradiation control device moves on to irradiating the beam to the next spot. Therefore, high measurement accuracy is required for the position monitor and dose monitor to deliver a sufficient dose to the tumor while minimizing damage to surrounding healthy tissue.

[0005] However, dose monitors have a known problem: the dose rate, which is the dose detected per unit time, affects measurement accuracy. An ionization chamber, a typical dose monitor, is a container filled with a fluid such as a gas or liquid between multiple electrodes. When a particle beam is incident, the fluid ionizes along the beam's trajectory, generating positive ions and electrons. By applying a voltage between the electrodes, the positive ions and electrons move to the opposite electrodes, creating a short-term current between the electrodes. The dose is calculated by measuring this current. However, as the dose rate increases, the density of the generated positive ions increases, increasing the proportion of positive ions and electrons that recombine before reaching the electrodes, reducing the collection efficiency of the dose monitor.

[0006] In conventional particle beam therapy, the dose rate is relatively low, so the decrease in the collection efficiency of the dose monitor is about 1%, and the impact on the linear response of the dose monitor is small. However, in recent years, ultra-high dose rate radiation therapy called FLASH radiation therapy has attracted attention, and the demand for irradiation at higher dose rates than conventional methods is increasing. Under high dose rates, the collection efficiency of the ionization chamber can decrease by several tens of percent, in which case the linear response of the dose monitor will break down. Therefore, in order to accurately control the dose delivered to the patient, it is necessary to understand the collection efficiency of the dose monitor.

[0007] Patent Document 1 discloses a technique for correcting the collection efficiency of an ionization chamber based on a pre-prepared prescription. In this technique, the dose rate and size of the beam irradiated to the patient during treatment are estimated as beam parameters based on the prescription. Based on the beam parameters, a correction coefficient for correcting the preset collection efficiency is determined for each spot. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6807125 Summary of the Invention [Problem to be solved by the invention]

[0009] However, because beam parameters fluctuate during particle beam irradiation, the beam parameters estimated based on a prescription do not necessarily match those of the actual particle beam. In particular, in particle beam irradiation at high dose rates, the fluctuations in beam parameters are significant enough to be unignorable. Therefore, the technology described in Patent Document 1 cannot adequately correct the collection efficiency of the dose monitor, making it difficult to accurately control the dose of the particle beam irradiated to the subject.

[0010] The present disclosure has been made in consideration of the above circumstances, and aims to provide a particle beam therapy system, an irradiation control device, and an irradiation control method that are capable of more accurately controlling the dose of a particle beam irradiated to a subject. [Means for solving the problem]

[0011] A particle therapy system according to one aspect of the present disclosure is a particle therapy system that irradiates a particle beam to a subject, and includes: a dose monitor that measures the dose of the particle beam; a position monitor that measures the beam size of the particle beam; and an irradiation control device that calculates measurement characteristics obtained by correcting the measurement characteristics of the dose monitor based on the dose and the beam size, and controls the irradiation of the particle beam to the subject based on the measurement characteristics and the dose. [Effects of the Invention]

[0012] According to the present invention, it is possible to more accurately control the dose of the particle beam irradiated onto the subject. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing the overall configuration of a particle beam therapy system according to a first embodiment of the present disclosure. [Figure 2] 1 is a diagram showing a configuration of an irradiation nozzle according to a first embodiment of the present disclosure. FIG. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a dose monitor according to the first embodiment of the present disclosure. [Figure 4] FIG. 1 is a diagram illustrating an example of the configuration of a position monitor according to a first embodiment of the present disclosure. [Figure 5] 10A and 10B are diagrams for explaining an example of a method for calculating the center position and size of a beam according to the first embodiment of the present disclosure. [Figure 6] 1 is a flowchart for explaining the operation of particle beam therapy according to the first embodiment of the present disclosure. [Figure 7] 1 is a diagram illustrating a configuration example of an irradiation control system according to a first embodiment of the present disclosure. [Figure 8] 10 is a flowchart illustrating an example of a monitoring process according to the first embodiment of the present disclosure. [Figure 9] FIG. 10 is a conceptual diagram of a collection efficiency table according to the first embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram showing an example of a method for determining the first spot in the second embodiment of the present disclosure. [Figure 11] FIG. 10 is a diagram illustrating the configuration of an irradiation control system according to a second embodiment of the present disclosure. [Figure 12] 10 is a flowchart illustrating an example of a monitoring process according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. [Example]

[0015] First, a particle beam therapy system and an irradiation control device according to a first embodiment of the present disclosure will be described with reference to FIGS.

[0016] Fig. 1 is a diagram showing the overall configuration of a particle therapy system according to the present embodiment. The particle therapy system 100 shown in Fig. 1 is a system that irradiates a particle beam 160 onto a patient 150 who is an examinee. In this embodiment, the particle therapy system 100 uses a spot scanning method or a raster scanning method that sequentially irradiates each of a plurality of spots, which are virtually set microscopic regions within the body of the patient 150.

[0017] As shown in FIG. 1, the particle beam therapy system 100 includes 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 / beam transport system control device 107, and an irradiation control device 108.

[0018] The accelerator system 101 is a group of devices that generate and extract the beam 160. In the example of FIG. 1, the accelerator system 101 includes an ion source 111, an injector 112, and a synchrotron accelerator 113. The ion source 111 generates charged particles that are the particles that form the beam 160. The injector 112 injects the charged particles generated by the ion source 111 into the synchrotron accelerator 113. The synchrotron accelerator 113 accelerates the charged particles injected from the injector 112 to generate and output the beam 160.

[0019] 1 is merely an example and is not limited to this example. For example, the accelerator system 101 may be a group of devices using a cyclotron accelerator or a synchrocyclotron accelerator instead of the synchrotron accelerator 113.

[0020] The beam transport system 102 is a group of devices that transport the beam 160 extracted from the accelerator system 101 to the irradiation nozzle 103. The beam transport system 102 has a beam path 121 and a bending electromagnet 122. The beam path 121 is the path along which the beam 160 travels, connecting the accelerator system 101 and the irradiation nozzle 103. The beam path 121 is in a vacuum state. The bending electromagnet 122 deflects the beam traveling along the beam path 121 using a magnetic field and transports the beam to the irradiation nozzle 103. The beam transport system 102 may or may not have a rotating gantry that adjusts the irradiation angle at which the beam 160 is irradiated onto the patient 150.

[0021] The irradiation nozzle 103 is an apparatus housing that includes a group of apparatuses, including an apparatus for irradiating the patient 150 with the beam 160 transported from the beam transport line 102, and an apparatus for measuring beam parameters related to the beam 160. A more detailed configuration of the irradiation nozzle 103 will be described later with reference to FIG.

[0022] The treatment table 104 is a bed on which the patient 150 rests. The treatment table 104 moves based on instructions 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 is capable of movement in six axial directions, including, for example, translational movement along each of three axes facing in different directions, and rotational movement around each of the three axes as a rotation axis.

[0023] The treatment planning device 105 creates a treatment plan for the patient 150, creates a prescription, and transmits the prescription to the overall control device 106. The prescription indicates, for each spot to be irradiated with the beam 160, a target dose, which is a target value of the dose of the beam 160 to be irradiated to that spot.

[0024] The overall control device 106 is connected to the treatment couch 104, the treatment planning device 105, the accelerator / beam transport system control device 107, and the irradiation control device 108, and controls each of the connected devices based on the prescription from the treatment planning device 105.

[0025] The accelerator / beam transport system controller 107 controls the accelerator system 101 and the beam transport system 102 based on instructions from the overall controller 106 .

[0026] The irradiation control device 108 controls the irradiation nozzle 103 based on instructions from the overall control device 106. The irradiation control device 108 also processes the measurement results from the irradiation nozzle 103 and transfers them to the overall control device 106. A more detailed configuration of the irradiation control device 108 will be described later with reference to FIG. 6.

[0027] The treatment planning system 105, the overall control system 106, the accelerator / beam transport system control system 107, and the irradiation control system 108 are realized by a computer system having, for example, a central processing unit (CPU), a memory, a storage device, a communication interface device, and a user interface (UI) device. Each of these devices performs various processes by, for example, reading and executing a program recorded in the memory by the central processing unit. The program of each device may be a single program, divided into multiple programs, or a combination thereof. Furthermore, some or all of the programs of each device may be realized by dedicated hardware or may be modularized. Furthermore, some or all of the programs may be installed in each device using a program distribution server or external storage medium (not shown). Furthermore, each device may be composed of independent devices connected to each other via a wired or wireless network, or two or more devices may be integrated.

[0028] FIG. 2 is a diagram showing an example of the configuration of the irradiation nozzle 103.

[0029] 2 includes an irradiation system 200 for irradiating the patient 150 with the beam 160, and a control system for controlling the irradiation system 200, which includes a dose monitor controller 206, a position monitor controller 207, and a scanning magnet controller 208. The irradiation system 200 includes scanning magnets 201A and 201B, a dose monitor 202, and a position monitor 203.

[0030] If necessary, the illumination system 200 may include a ridge filter 204 that expands the Bragg peak of the beam 160 in the traveling direction of the beam 160, and a range shifter 205 that adjusts the depth that the beam 160 reaches.

[0031] The scanning magnets 201A and 201B are a scanning system that scans the beam 160 in a plane (two-dimensional direction) perpendicular to the passing direction of the beam 160. The beam 160 scanned by the scanning magnets 201A and 201B is irradiated onto a target volume 151 in the patient 150. The target volume 151 is an irradiation region to be irradiated with the beam 160, and for example, when the particle therapy system 100 treats a tumor such as cancer in the patient 150, the target volume 151 is an area obtained by adding a margin (a margin region that takes into account an error in the irradiation position) to the tumor region where the tumor exists. The spot to be irradiated with the beam 160 is set within the target volume 151.

[0032] The dose monitor 202 is a monitor for measuring the dose rate of the beam 160 irradiated to each spot. The dose monitor 202 outputs a detection signal indicating the measurement result to the dose monitor controller 206. The dose monitor controller 206 calculates the dose rate of the beam 160 irradiated to each spot based on the detection signal from the dose monitor 202, and outputs the calculated dose rate to the irradiation controller 108.

[0033] Fig. 3 is a diagram showing an example of the dose monitor 202. The dose monitor 202 shown in Fig. 3 is a commonly used parallel plate type ionization chamber.

[0034] The dose monitor 202, which is a parallel-plate ionization chamber shown in FIG. 3, is covered with a shielding wall 301, and multiple beam windows 302 with high transmittance for the beam 160 are formed in the shielding wall 301. Specifically, the beam windows 302 are formed at opposing positions on the shielding wall 301 so that the beam 160 entering through one beam window 302 is emitted from the other beam window. Furthermore, one or more flat-plate-shaped high-voltage electrodes 303 and one or more flat-plate-shaped collecting electrodes 304 are arranged in parallel in the space surrounded by the shielding wall 301. In the example of FIG. 3, the dose monitor 202 has one high-voltage electrode 303 and two collecting electrodes 304 arranged on either side of 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. Furthermore, the spaces between the electrodes 303-304 are filled with gas.

[0035] The beam 160 that passes through the beam window 302 and enters the dose monitor 202 ionizes the gas between the electrodes 303 and 304, generating positive ions and electrons. The generated positive ions and electrons are moved to the collecting electrode 304 by the electric field generated between the electrodes 303 and 304. This movement of the positive ions and electrons causes a current 305 to flow between the electrodes 303 and 304, which is measured by the dose monitor control device 206.

[0036] There is a proportional relationship between the dose of the beam 160 and 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. Note that the dose rate calculated by the dose monitor control device 206 is an uncorrected dose rate, which is a dose rate that does not take into account fluctuations in the collection efficiency of the dose monitor 202.

[0037] The dose monitor 202 is not limited to the example shown in Fig. 3. For example, the spaces between the electrodes 303-304 may be filled with a liquid or may be open to the air. The shape of the electrodes 303-304 is not limited to a flat plate, and may be, for example, a coaxial cylindrical shape. The dose monitor 202 is not limited to an ionization chamber, and may be any monitor whose measurement characteristics change depending on the dose rate and beam size.

[0038] Returning to the explanation of Fig. 2, the position monitor 203 is a monitor for measuring the center position and beam size of the beam 160. The position monitor 203 outputs a detection signal indicating the measurement result to the position monitor controller 207. The position monitor controller 207 calculates the center position and beam size of each beam based on the detection signal input from the position monitor 203, and outputs the calculated values ​​to the irradiation controller 108.

[0039] Fig. 4 is a diagram showing an example of the position monitor 203. The position monitor 203 shown in Fig. 4 is a commonly used multi-strip ionization chamber.

[0040] Similar to the dose monitor 202 shown in FIG. 3, the multi-strip ionization chamber serving as the position monitor 203 is covered with a shielding wall (not shown), and multiple beam windows 401 with high transmittance for the beam 160 are formed in the shielding wall. Specifically, the beam windows 402 are formed at opposing positions on the shielding wall so that the beam 160 entering through one beam window 402 is emitted from the other beam window. In addition, one or more flat high-voltage electrodes 402 and one or more flat collecting electrodes 403A and 403B are arranged in parallel in the space surrounded by the shielding wall. A high voltage is applied to the high-voltage electrode 402, and an electric field is generated between the high-voltage electrode 402 and the collecting electrodes 403A and 403B. In addition, the spaces between the electrodes 402, 403A, and 403B are filled with a fluid such as a gas or a liquid.

[0041] Collector 403A is composed of a plurality of small, rectangular collector electrodes arranged in parallel in one direction (defined as the X direction) within the plane, and collector 403B is composed of a plurality of small, rectangular collector electrodes arranged in parallel in a direction (defined as the Y direction) perpendicular to the X direction within the plane.

[0042] The beam 160, which passes through the beam window 401 and enters the position monitor 203, ionizes the fluid between the electrodes 402-403, generating positive ions and electrons. The generated positive ions and electrons are transported to the nearby small collector electrodes 304A or 304B by the electric field generated between the electrodes 402-403. This movement of positive ions and electrons generates a current 404, which is measured for each small collector electrode by the position monitor controller 207. This allows the position monitor controller 207 to measure the two-dimensional distribution of ions generated in the in-plane direction of the collector electrode 304A or 304B, and thus the dose distribution, based on the current 404 for each small collector electrode. From this dose distribution, the center position and beam size of the beam 160 can be calculated.

[0043] Fig. 5 is a diagram illustrating an example of a method for calculating the center position and beam size of beam 160. In Fig. 5, the horizontal axis indicates the center position in the X direction of each small collecting electrode of collecting electrode 403A, and the vertical axis indicates the current value. Each data point 501 in Fig. 5 represents the current value indicated by the detection signal of each small collecting electrode.

[0044] Assuming that the shape of the beam 160 follows a Gaussian distribution, when the distribution of data points 501 is approximated by a Gaussian function 502, a peak position 503 and a standard deviation 504 respectively become the center position and the beam size of the beam 160. Note that, for simplicity, an example of a one-dimensional distribution is shown in Fig. 5, but in reality, a two-dimensional dose distribution is approximated by a two-dimensional Gaussian function.

[0045] The method for calculating the center position and beam size of the beam 160 is not limited to the above example, and the dose distribution may be approximated by a Lorentz function, assuming that the shape of the beam 160 follows a Lorentz distribution. The position monitor 203 is not limited to the example shown in Fig. 3. For example, the position monitor 203 may be a multi-wire ionization chamber.

[0046] Returning to the explanation of Fig. 2, the irradiation controller 108 calculates the irradiation position of the beam 160 from the center position of the beam 160 calculated by the position monitor controller 207. Furthermore, the irradiation controller 108 calculates the collection efficiency, which is a measurement characteristic of the dose monitor 202, based on the beam parameters (dose rate, center position, and beam size) transmitted from the dose monitor controller 206 and the position monitor controller 207. The irradiation controller 108 calculates a corrected dose rate that takes into account fluctuations in the collection efficiency by correcting the dose rate calculated by the dose monitor controller 206 based on the collection efficiency.

[0047] Next, the operation of the particle therapy system 100 will be described.

[0048] FIG. 6 is a flowchart for explaining an example of a treatment process for treating the patient 150 in the particle beam therapy system 100. As shown in FIG.

[0049] In particle beam therapy, typically, a high-dose beam 160 is applied to the patient 150 at one time, and in order to prevent damage to normal tissues of the patient 150, fractionated irradiation is performed in which the beam is irradiated to the patient 150 in multiple doses. In this embodiment, the fractional unit is one day, and the number of fractional units is 30. However, the fractional unit and the number of fractional units are not limited to these examples. For example, the fractional unit does not have to be one day, and multiple treatments may be performed in one day.

[0050] First, when treatment on the day (day d) starts (step S601), the treatment planning device 105 creates a prescription, which is a treatment plan (step S602). The initial value of d is 1.

[0051] Specifically, in step S602, the treatment planning device 105 first reads an in-vivo image of the periphery of a tumor, which is the affected area of ​​the patient 150, and converts the thickness distribution from the body surface of the patient 150 to the affected area into a distribution of water equivalent thickness ratios based on the in-vivo image. The in-vivo image is created, for example, by a CT (Computed Tomography) examination. The water equivalent thickness ratio is the ratio between the thickness of water that causes the same energy loss to the beam 160 and the thickness of a local medium, and is a physical quantity that determines the stopping distance of the beam 160.

[0052] Next, the treatment planning device 105 uses the in-vivo image to determine the contour of the target volume 151, which is a three-dimensional irradiation region to be irradiated with the beam 160. For example, the treatment planning device 105 displays the in-vivo image to allow an operator such as a doctor to draw the contour of a tumor, and determines the contour of the target volume 151 by adding a predetermined margin to the contour of the tumor.

[0053] Furthermore, the treatment planning device 105 creates a prescription (a target dose set for each spot). 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 creates the prescription by calculating the spot positions and target doses for applying the target dose to the target volume 151 based on the distribution of the water equivalent thickness ratio, using a predetermined optimization calculation method or the like. The treatment planning device 105 displays the prescription, and when the operator approves the prescription, transmits the prescription to the overall control device 106.

[0054] Based on the prescription from the treatment planning system 105, the overall controller 106 creates control instruction data for each spot to control the accelerator / beam transport system controller 107 and the irradiation controller 108, and transmits the control instruction data to the accelerator / beam transport system controller 107 and the irradiation controller 108. The transmitted data is stored in memories (not shown) in the accelerator / beam transport system controller 107 and the irradiation controller 108. The control instruction data for the accelerator / beam transport system controller 107 includes, for example, the excitation current values ​​of the electromagnets of the accelerator system 101 and the beam transport system 102, which are determined according to the beam energy corresponding to the depth of the spot position, and the radio-frequency power value to be applied to the radio-frequency acceleration cavity. The control instruction data for the irradiation controller 108 includes, for example, the target dose and the current values ​​of the scanning electromagnets 201A and 201B.

[0055] This completes the process of step S602. If the prescription is not approved by the operator, the target dose is reset.

[0056] Thereafter, the patient 150 is placed on the treatment couch 104, and the patient 150 is positioned so as to coincide with the time of capturing the in-vivo image, and the operator instructs the particle beam therapy system 100 to irradiate the beam 160 (step S603).

[0057] Then, the overall controller 106 transmits an instruction to start irradiation of the spot to be irradiated (assumed to be the nth spot) to the accelerator / beam transport system controller 107 and the irradiation controller 108 (step S604). The initial value of n is 1.

[0058] Upon receiving the irradiation start command, the accelerator / beam transport system controller 107 starts accelerating the beam 160 in accordance with the control command data stored in the memory. When the acceleration of the beam 160 is completed, the irradiation controller 108 changes the current values ​​of the scanning magnets 201A and 201B via the scanning magnet controller 208. When the change in the current values ​​is completed, the accelerator / beam transport system controller 107 extracts the beam 160. The extracted beam 160 passes through the beam transport system 102 and the irradiation nozzle 103 and is irradiated onto the target volume 151 of the patient 150. The dose monitor 202 and the position monitor 203 measure beam parameters of the beam 160, and the irradiation controller 108 calculates the dose of the beam 160 for the n-th spot based on the beam parameters (step S605).

[0059] Thereafter, when the dose reaches the target dose, the irradiation control device 108 transmits an end signal to the overall control device 106 indicating the end of irradiation of the beam 160 onto the n-th spot. Upon receiving the end signal, the overall control device 106 executes an end process, which is a process for ending irradiation of the beam 160 onto the n-th spot (step S606). The end process is a process for stopping irradiation of the beam 160 when a spot scanning method is used in which movement between spots is performed while the beam is stopped, and is a process for proceeding to preparation for irradiation of the next spot when a raster scanning method is used in which movement between spots is performed while the beam is being irradiated.

[0060] Then, the overall control device 106 determines whether or not irradiation of the beam 160 onto the last spot has been completed (step S607).

[0061] If irradiation of the beam 160 to the last spot has not been completed, the overall control device 106 increments n and instructs the accelerator / beam transport system control device 107 and the irradiation control device 108 to prepare for irradiation of the next spot (step S608), and returns to the processing of step S604.

[0062] On the other hand, when irradiation of the beam 160 to the last spot is completed, the treatment for that day is completed. Then, the overall control device 106 determines whether it is the last day. If it is not the last day, the process of step S601 is executed, and if it is the last day, the process is completed.

[0063] The irradiation controller 108 may be directly connected to the accelerator / beam transport system controller 107 and may transmit various signals directly to the accelerator / beam transport system controller 107 .

[0064] The irradiation dose monitoring process, which is the process of steps S604 to S606 in FIG. 6, will now be described in more detail.

[0065] Fig. 7 is a diagram showing an example of the configuration of an irradiation control system including an irradiation nozzle 103 and an irradiation control device 108. Fig. 8 is a flowchart for explaining an example of monitoring processing by the irradiation control system shown in Fig. 7. The following will explain an example of irradiation of the beam 160 onto the n-th spot.

[0066] 7, the dose monitor control device 206 includes 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 a dose rate based on the pulse signal converted by the I / F converter 702. The pulse frequency of the pulse signal represents the dose rate. The position monitor control device 207 includes 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 beam size of the beam 160 based on the pulse signal converted by the I / F converter 704.

[0067] The irradiation control device also includes a memory 701 that stores control instruction data (target dose for each spot), and a CPU 707. The CPU 707 also includes a counter 703 that counts the number of pulses.

[0068] When step S604 starts, the overall controller 106 first transmits an irradiation start instruction to the accelerator / beam transport system controller 107 and the irradiation controller 108 (step S801). Upon receiving the irradiation start instruction, the accelerator / beam transport system controller 107 accelerates and extracts the beam 160 in accordance with the control instruction data stored in the memory (step S803).

[0069] During the period from when the irradiation start command is received until the beam 160 is extracted by the accelerator / beam transport system control device 107 (between steps S801 and S803), the CPU 707 of the irradiation control device 108 reads the target dose corresponding to the n-th spot from the target doses stored in the memory 701 in step S602. In this embodiment, the current output from the dose monitor 202 is converted into a pulse signal by the I / F converter 702 of the dose monitor control device 206, and the number of pulses in the pulse signal represents the dose. Therefore, the CPU 707 converts the target dose into a target pulse number, which is calculated as the number of pulses, and sets the target pulse number in the counter 703 (step S802).

[0070] The conversion factor for converting the target dose into the target number of pulses is determined depending on the characteristics of the dose measurement circuit including the dose monitor 202 and the I / F converter 702. Note that the process of step S802 may be performed during the period from the completion of irradiation of the beam 160 to the previous spot (the n-1th spot) until an irradiation start instruction to that spot is transmitted.

[0071] Then, when the beam 160 is emitted (step S803), the currents detected by the dose monitor 202 and the position monitor 203 during irradiation of the target volume 151 with the beam 160 are converted into pulse signals by I / F converters 702 and 704 in the dose monitor controller 206 and the position monitor controller 207, respectively. As described with reference to FIG. 3, the CPU 705 of the dose monitor controller 206 calculates the dose rate of the beam 160 from the pulse signal and transmits it to the irradiation controller 108. Furthermore, as described with reference to FIG. 4, the CPU 706 of the position monitor controller 207 calculates the center position and beam size of the beam 160 from the two-dimensional distribution of the pulse frequency of the pulse signal and transmits it to the irradiation controller 108 (step S804). Note that the conversion coefficient for converting the current into a pulse signal is a constant determined depending on the characteristics of the dose measurement circuit, similar to the conversion coefficient for the target dose described above.

[0072] The CPU 707 of the irradiation controller 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).

[0073] As an example of a method for calculating collection efficiency, a calculation method based on a theoretical formula will be described below.

[0074] Assuming that the spread of the beam 160 follows a Gaussian distribution, the beam current density i(r) of the beam 160 at a distance r from the center of the beam 160 is described by the following equation 1 using the actual integrated beam current I and beam size σ of the beam 160. Note that the distance r is the distance in a direction within a plane perpendicular to the traveling direction of the beam 160.

number

number

number

number

[0075] The above-described method for calculating the collection efficiency is merely an example, and the present invention is not limited to this method. For example, although it is assumed that the spread of the beam 160 follows a Gaussian distribution, if the spread of the beam 160 is a distribution determined according to the integrated beam current and the beam size, it may be assumed that the spread of the beam 160 follows a Lorentzian distribution or the like.

[0076] Alternatively, instead of calculating the collection efficiency from the theoretical formula (4), a collection efficiency table showing the relationship between the dose rate and the beam size σ and the collection efficiency may be used. In this method, the CPU 707 of the irradiation controller 108 calculates the collection efficiency by referring to the collection efficiency table created in advance.

[0077] Fig. 9 is a diagram showing an example of a collection efficiency table. The collection efficiency table 900 shown in Fig. 9 is a matrix table in which rows correspond to dose rates and columns correspond to beam sizes, and each element represents the collection efficiency according to the dose rate and beam size corresponding to its row and column.

[0078] A method for creating the collection efficiency table includes a method in which measurements are performed using the dose monitor 202 for a beam with a known dose rate and beam size, and the process of calculating the collection efficiency by comparing the ideal dose rate with the measured dose rate is repeatedly performed while changing the dose rate and beam size.

[0079] 7 and 8. After the process of step S805 is completed, the CPU 707 of the irradiation controller 108 multiplies the pulse frequency of the pulse signal from the dose monitor controller 206 by the inverse of the collection efficiency to obtain a corrected pulse frequency corresponding to a corrected dose rate, which is a dose rate that takes fluctuations in the collection efficiency into consideration. The CPU 707 integrates the corrected pulse frequency using the counter 703 to count the number of correction pulses corresponding to a corrected dose obtained by correcting the measured dose, which is the dose applied to the n-th spot, by the collection efficiency (step S806).

[0080] 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). If the correction dose has not reached the target dose, the process of step S804 is executed again. If the correction dose has reached the target dose, the irradiation dose monitoring process is terminated and the process of step S606 in Fig. 6 is executed.

[0081] Next, the effects of this embodiment will be described.

[0082] According to this 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 characteristics of the dose monitor 202 based on the dose and beam size of the beam 160, and controls the irradiation of the beam 160 to the patient 150 based on the measurement characteristics and the dose. Therefore, since the irradiation of the beam 160 to the patient 150 is controlled based on the measurement characteristics of the dose monitor 202 calculated from the actually measured dose and beam size of the beam 160, it is possible to more accurately control the dose of the beam 160 irradiated to the patient 150.

[0083] Furthermore, in this embodiment, the irradiation controller 108 calculates a corrected dose based on the measurement characteristics, and when the integrated value of the corrected dose reaches the target dose, executes processing to terminate irradiation of the beam 160. Therefore, since it is only necessary to correct the dose and the setting of the target dose and the like can be performed in the same manner as in the conventional method, there is no need to change the processing system, i.e., there is no need to add or change existing hardware devices, and additional costs can be reduced.

[0084] Furthermore, in this embodiment, the collection efficiency of the ionization chamber is used as the measurement characteristic of the dose monitor 202. This makes it possible to use a general dose monitor 202, thereby making it possible to suppress additional costs. [Example]

[0085] Next, a particle therapy system and an irradiation control device according to a second embodiment of the present disclosure will be described with reference to Figures 10 to 12. Differences from the first embodiment will be mainly described below. Note that the same reference numerals are used to designate the same components as those in the first embodiment.

[0086] The overall configuration of the particle therapy system 100 of the second embodiment is similar to the overall configuration of the particle therapy system 100 of the first embodiment shown in FIG. 1 . However, in this embodiment, the irradiation control device 108 calculates a corrected target dose by correcting the target dose based on the collection efficiency of the dose monitor 202, instead of correcting the dose. When the integrated value of the dose measured by the dose monitor 202 reaches the corrected target dose, the irradiation control device 108 executes a termination process to terminate the irradiation of the beam 160. The calculation of the corrected target dose is performed for each spot, and the collection efficiency used to calculate the corrected target dose for each spot is calculated based on the dose and beam size of the beam 160 irradiated to a reference spot, which is a spot that precedes the irradiation spot in the irradiation order. In this embodiment, the collection efficiency of each spot is calculated based on the dose and beam size of the beam 160 irradiated to the spot immediately preceding the spot in the irradiation order.

[0087] When the difference in the characteristics of the beam 160 between the reference spot and the irradiation spot is sufficiently small, the collection efficiency can be calculated with high accuracy even in this embodiment, enabling highly accurate irradiation control. For example, when the periodic fluctuation scale of the beam parameters is longer than the irradiation time for one spot and the difference in beam parameters between adjacent spots is smaller than the difference between the irradiation instruction and the actual irradiation, by referring to the average value of the beam parameters for the immediately preceding spot, it is possible to calculate the collection efficiency with higher accuracy than calculating the collection efficiency based on a prescription.

[0088] The overall flow of the treatment process for treating the patient 150 in this embodiment is similar to the overall flow of the treatment process described using Fig. 6. However, for the first spot to be initially irradiated with the beam 160, the dose and beam size of the beam 160 for calculating the corrected target dose cannot be obtained. Therefore, when creating the prescription in step S602, the irradiation control device 108 performs additional processing to reduce the impact on the treatment quality of an error in the dose to be applied to the first spot.

[0089] The addition process is a process of determining a spot that satisfies a predetermined condition as the first spot from a plurality of spots obtained by dividing the target volume 151. For example, in the addition process, the first spot is determined based on the target volume 151.

[0090] Fig. 10 is a diagram showing an example of the first spot. In the example of Fig. 10, the first spot is set to spot 1001, which is closest to the center of target volume 151. In this case, it is considered that there is no or little normal tissue near spot 1001, so the impact of dose errors on treatment quality can be reduced.

[0091] The first spot shown in FIG. 10 is merely an example and is not limited thereto. For example, the first spot may be a spot that is a certain distance or more from a predetermined organ. Alternatively, the first spot set by any method may be further divided into a plurality of subdivided spots, and one of the subdivided spots may be reset as the first spot. In this case, it is possible to reduce the target dose for the subdivided spots, thereby reducing the dose applied to the subdivided spots, thereby reducing the impact of dose errors on treatment quality.

[0092] The additional processing may be automated by a program in the irradiation control device 108, or may be processing in which the target volume 151 and each spot are displayed and the operator is prompted to select them.

[0093] The irradiation dose monitoring process (the processes of steps S604 to S606 in FIG. 6) in the second embodiment will be described in more detail below.

[0094] Fig. 11 is a diagram showing an example of the configuration of an irradiation control system including an irradiation nozzle 103 and an irradiation control device 108. Fig. 12 is a flowchart for explaining an example of monitoring processing by the irradiation control system shown in Fig. 11. In the following, irradiation of the n-th spot with the beam 160 will be described as an example.

[0095] After starting irradiation of the n-th spot, the overall controller 106 transmits an irradiation start instruction to the accelerator / beam transport system controller 107 and the irradiation controller 108 (step S1201). Upon receiving the irradiation start instruction, the accelerator / beam transport system controller 107 accelerates and extracts the beam 160 in accordance with the control instruction data stored in the memory (step S1204).

[0096] The CPU 707 of the irradiation controller 108 executes the following steps S1202 to S1203 from the time when it receives the irradiation start command until the accelerator / beam transport system controller 107 extracts the beam 160.

[0097] First, the CPU 707 calculates the collection efficiency of the dose monitor 202 based on the average dose rate and average size of the beam 160 irradiated onto the previous spot (the n-1th spot) stored in the memory 701 (step S1202). The average dose rate is the average value of the dose rates of the beam 160 irradiated onto the previous spot, and the average size is the average value of the beam sizes of the beam 160 irradiated onto the previous spot. The average dose rate is the average value of the dose rates that have not been corrected based on the collection efficiency. The method of calculating the collection efficiency may be a method using theoretical formula (4) as in the first embodiment, or a method using a table such as that shown in FIG. 9.

[0098] Note that when n=1, that is, when the first spot is irradiated with the beam 160, there is no average dose rate or average size corresponding to the previous spot. Therefore, the CPU 707 may set a fixed value (e.g., 1) as the collection efficiency, or may roughly calculate the collection efficiency based on the average dose rate and average size estimated from the prescription.

[0099] Next, the CPU 707 reads the target dose of the n-th spot from the memory 701, and calculates a corrected target dose by correcting the target dose based on the collection efficiency. The CPU 707 converts the corrected target dose into a corrected target pulse number converted into the number of pulses, and sets the corrected target pulse number in the counter 703 (step S1203).

[0100] Then, when the beam 160 is emitted (step S1204), the currents detected by the dose monitor 202 and the position monitor 203 during irradiation of the target volume 151 with the beam 160 are converted into pulse signals by I / F converters 702 and 704 in the dose monitor controller 206 and the position monitor controller 207, respectively, and output. The CPU 707 of the irradiation controller 108 transmits the pulse signal output from the I / F converter 702 to a counter 703 to count the number of pulses. That is, in this embodiment, unlike the first embodiment, correction of the dose rate based on the collection efficiency is not performed. Furthermore, the CPU 706 of the position monitor controller 207 calculates the center position and beam size of the beam 160 based on the pulse signal output from the I / F converter 702 (step S1205).

[0101] The CPU 707 of the irradiation control device 108 determines whether the accumulated number of pulses has reached the corrected target number of pulses for the nth spot read from the memory 701, thereby determining whether the dose applied to the nth spot has reached the corrected target dose (step S1206).

[0102] If the dose has not reached the corrected target dose, the process returns to step S1205. On the other hand, if the dose has reached the corrected target dose, the CPU 705 of the dose monitor control device 206 calculates the average value of the dose rates of the beam 160 irradiated onto the first spot as a pre-correction average dose rate and records it in the memory 701 of the irradiation control device 108. The CPU 706 of the position monitor control device 207 also calculates the average value of the beam sizes of the beam 160 irradiated onto the first spot as an average size and records it in the memory 701 of the irradiation control device 108 (step S1207), and then ends the process. The pre-correction average dose rate and the average size may be collectively referred to as average irradiation parameters. The pre-correction average dose rate is a name given for convenience, and in this embodiment, the dose rate is not corrected.

[0103] In the above operation, the timing for calculating the average irradiation parameters and collection efficiency is not limited to the timing described with reference to Fig. 12. For example, the average irradiation parameters may be calculated based on the number of pulses accumulated up to a predetermined time point before the irradiation of the beam 160 ends, or the collection efficiency may be calculated between the timing at which the irradiation of the beam 160 ends and the timing at which irradiation of the next spot starts.

[0104] In the above example, the reference spot is the spot immediately preceding the target spot, but this is not limiting. For example, the irradiation controller 108 may select, as the reference spot, a spot whose beam parameters are closest to those of the beam 160 irradiating the target spot, based on the fluctuation trends of the beam parameters of the beam 160.

[0105] Next, the effects of this embodiment will be described.

[0106] As described above, according to this embodiment, the irradiation controller 108 calculates a corrected target dose by correcting a predetermined target dose based on the measurement characteristics, and when the integrated value of the dose reaches the corrected target dose, executes a process to terminate irradiation of the beam 160. Therefore, as in the first embodiment, the target dose can be set in the same way as in the conventional case, and no changes are required to the processing system. Therefore, there is no need to add or change existing hardware devices, and additional costs can be reduced.

[0107] Furthermore, in this embodiment, the irradiation control device 108 calculates the corrected target dose for each spot based on the dose and beam size of the beam 160 irradiated to the spot immediately before that spot. Therefore, it is not necessary to correct the dose of the beam 160 in real time, and it is possible to prevent delays in the decision to terminate irradiation of the beam 160 due to the processing time required for correction, and it is possible to prevent unnecessary irradiation.

[0108] Furthermore, in this embodiment, the irradiation control device 108 calculates the corrected target dose for each spot based on the dose and beam size of the beam 160 that irradiated the spot one spot lower than the spot. This allows the corrected target dose to be calculated based on the dose and beam size of the beam 160 that is considered to have the closest characteristics to the beam 160, making it possible to more accurately control the dose of the beam 160 irradiated to the patient 150.

[0109] In this embodiment, a spot that satisfies a predetermined condition is set as the first spot to be first irradiated with the beam 160. This makes it possible to reduce the impact on treatment quality due to an error in the irradiation dose at the first spot.

[0110] The present disclosure is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present disclosure is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is also possible to add, delete, or replace part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0111] 100: Particle beam therapy system 101: Accelerator system 102: Beam transport system 103: Irradiation nozzle 104: Treatment table 105: Treatment planning system 106: Overall control device 107: Accelerator / beam transport system control device 108: Irradiation control device 111: Ion source 112: Injector 113: Synchrotron accelerator 121: Beam path 122: Bending magnet 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

Claims

1. A particle beam therapy system that irradiates a particle beam to a subject, a dose monitor for measuring the dose of the particle beam; a position monitor for measuring a beam size of the particle beam; an irradiation control device that calculates a measurement characteristic of the dose monitor based on a dose measured by the dose monitor, the beam size, and a constant determined by a structure of the dose monitor, and controls irradiation of the particle beam to the subject based on the measurement characteristic and the dose measured by the dose monitor, the dose monitor has one high-voltage electrode and one collecting electrode; A particle beam therapy system, wherein the constant is the distance between the high-voltage electrode and the collecting electrode.

2. A particle beam therapy system that irradiates a particle beam to a subject, comprising: a dose monitor for measuring the dose of the particle beam; a position monitor for measuring a beam size of the particle beam; and an irradiation control device that calculates the measurement characteristics based on the dose and the beam size measured by the dose monitor, and a collection efficiency table showing a relationship between the dose rate and the beam size measured by the dose monitor and the measurement characteristics of the dose monitor, and controls the irradiation of the particle beam to the subject based on the measurement characteristics and the dose measured by the dose monitor.

3. 2. The particle beam therapy system according to claim 1, wherein the irradiation control device calculates a corrected dose by correcting the dose measured by the dose monitor based on the measurement characteristics, and when an integrated value of the corrected dose reaches a target dose, executes a process of terminating the irradiation of the particle beam.

4. the target dose is set in advance for each of a plurality of micro-regions in the subject to be irradiated with the particle beam; 4. The particle therapy system according to claim 3, wherein the irradiation control device irradiates each of the plurality of microregions with the particle beam in turn, and when the corrected dose of the particle beam irradiating any one of the microregions reaches the target dose for that microregion, the irradiation control device executes a process of terminating the irradiation of the particle beam to that microregion.

5. 2. The particle beam therapy system according to claim 1, wherein the irradiation control device calculates a corrected target dose by correcting a predetermined target dose based on the measurement characteristics, and when an integrated value of the dose measured by the dose monitor reaches the corrected target dose, executes a process of terminating the irradiation of the particle beam.

6. the target dose is set in advance for each of a plurality of micro-regions in the subject to be irradiated with the particle beam; 6. The particle therapy system according to claim 5, wherein the irradiation control device irradiates each of the plurality of micro-regions with the particle beam in turn, and when a dose of the particle beam irradiated to any one of the micro-regions measured by the dose monitor reaches the corrected target dose for that micro-region, the irradiation control device executes a process of terminating the irradiation of the particle beam to that micro-region.

7. 7. The particle beam therapy system according to claim 6, wherein the irradiation control device calculates the corrected target dose for each micro-region excluding the micro-region to be first irradiated with the particle beam based on the dose measured by the dose monitor of the particle beam irradiated to a micro-region that precedes the micro-region in the irradiation order to be irradiated with the particle beam and the beam size.

8. 8. The particle beam therapy system according to claim 7, wherein the irradiation control device calculates the corrected target dose for each microregion based on the dose measured by the dose monitor of the particle beam irradiated to the microregion immediately preceding the microregion in the irradiation order.

9. The particle beam therapy system according to claim 6 , wherein the irradiation control device determines the micro-region that satisfies a predetermined condition as the micro-region to be first irradiated with the particle beam.

10. the dose monitor is an ionization chamber; The particle therapy system of claim 1 , wherein the measurement characteristic is a collection efficiency of the ionization chamber.

11. an irradiation control device connected to a dose monitor that measures a dose of a particle beam irradiated to a subject and a position monitor that measures a beam size of the particle beam, calculating a measurement characteristic of the dose monitor based on the dose measured by the dose monitor and the beam size; an irradiation control device that controls irradiation of the particle beam onto the subject based on the measurement characteristics and the dose measured by the dose monitor;

12. 1. An irradiation control method for a particle therapy system that irradiates a particle beam to a subject, comprising: the particle beam therapy system measures a dose of the particle beam with a dose monitor; the particle beam therapy system measures a beam size of the particle beam; the particle beam therapy system calculates a measurement characteristic of the dose monitor based on a dose measured by the dose monitor, the beam size, and a constant determined by a structure of the dose monitor; the particle beam therapy system controls irradiation of the particle beam to the subject based on the measurement characteristics and the measured dose; the dose monitor has one high-voltage electrode and one collecting electrode; The irradiation control method, wherein the constant is a distance between the high-voltage electrode and the collecting electrode.

13. An irradiation control method for a particle beam therapy system that irradiates a subject with a particle beam, comprising: the particle beam therapy system measures a dose of the particle beam with a dose monitor; the particle beam therapy system measures a beam size of the particle beam; the particle beam therapy system calculates the measurement characteristics based on the measured dose and beam size, and a collection efficiency table showing a relationship between the dose rate and beam size measured by the dose monitor and the measurement characteristics of the dose monitor; an irradiation control method, in which the particle beam therapy system controls irradiation of the particle beam to the subject based on the measurement characteristics and the measured dose;

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