Patent Description:
In recent years, a particle therapy for irradiating a tumor of a patient with particle beams such as a proton beam and a carbon beam has attracted attention. The particle therapy uses a phenomenon called a Bragg peak in which a high dose is applied to the surroundings immediately before a particle beam stops, and it is thus possible to form a dose distribution matching the shape of a tumor more easily as compared with an X-ray therapy or the like. As a result, implementation of a highly accurate radiotherapy is expected.

In the particle therapy, a charged particle beam (hereinafter, simply referred to as a particle beam) accelerated by an accelerator system including a linear accelerator, a synchrotron, or the like is transported as a particle beam to an irradiation nozzle, and is used to irradiate a tumor in a patient's body. Examples of a main beam irradiation method include a passive method and a scanning method. The passive method is a method of matching the shape of a particle beam to the shape of a tumor by expanding a spot size using a scatterer, a ridge filter, a collimator, a patient bolus, or the like. The scanning method is a method in which an irradiation direction of a thin particle beam called a pencil beam is adjusted by a scanning magnet in a container called an irradiation nozzle, and each of a plurality of minute regions (hereinafter, referred to as spots) virtually set in a tumor is sequentially irradiated with the particle beam to irradiate the entire tumor. In addition, examples of the scanning method include a spot scanning irradiation method in which movement between spots is performed in a state where a particle beam is stopped, and a raster scanning irradiation method in which movement between spots is performed in a state where irradiation with a particle beam is performed. In recent years, since it is possible to cope with a complicated tumor shape and its change, facilities adopting the scanning method are increasing.

In the scanning method, a particle beam is monitored by a position monitor and a dose monitor installed in the irradiation nozzle, and an irradiation dose is controlled for each spot based on the monitoring result. The position monitor measures the center position and size of a particle beam, and the dose monitor measures the magnitude of a dose. The irradiation control apparatus calculates an integral dose which is an integral value of irradiation doses with which the spot is irradiated based on these measured values, and once the integral dose reaches a target dose (hereinafter, referred to as a prescription) set in advance for each spot, the irradiation control apparatus performs irradiation of the next spot with a beam. Therefore, in order to suppress damage to surrounding healthy tissues while applying a sufficient dose to a tumor, high measurement accuracy is required for the position monitor and the dose monitor.

However, there is a known problem that, in the dose monitor, a dose rate, which is a dose detected per unit time, affects measurement accuracy. An ionization chamber, which is a general dose monitor, is a container in which gaps between a plurality of electrodes are filled with a fluid such as a gas or a liquid, and when a particle beam is incident, the fluid is ionized on a trajectory of the particle beam, whereby cations and electrons are generated. As a voltage is fed between electrodes, each of cations and electrons move to the opposite electrode, so that a current flows between the electrodes only for a short time. The dose is calculated by measuring the current. However, since the density of the generated cations increases as the dose rate increases, a ratio at which the cations and the electrons recombine before reaching the electrode increases, and collection efficiency in collecting the cations and the electrons in the dose monitor decreases.

In the particle therapy according to the related art, since the dose rate is relatively low, the decrease in collection efficiency of the dose monitor is about <NUM>%, and an influence on a linear responsiveness of the dose monitor is small. However, in recent years, a radiotherapy with an ultra-high dose rate called FLASH radiotherapy has attracted attention, and there is an increasing demand for irradiation with a higher dose rate than that according to the related art. A high dose rate may cause a decrease in collection efficiency of the ionization chamber by about several <NUM>%, and in this case, the linear responsiveness of the dose monitor is poor. Therefore, in order to control a dose applied to a subject with high accuracy, it is required to grasp the collection efficiency of the dose monitor.

<CIT> discloses a technology for correcting collection efficiency of an ionization chamber based on a prescription prepared in advance. In this technology, the dose rate and size of a beam with which a patient is irradiated at the time of treatment are estimated as beam parameters based on a prescription. A correction coefficient for correcting a preset collection efficiency is determined for each spot based on the beam parameters. Furthermore, <CIT> discloses a system and a method for improving the quality of beam delivery in a system for proton therapy by pencil beam scanning of a predeterminable volume within a patient that minimizes the extent of possible beam position errors to an extent medically acceptable.

However, since the beam parameter varies during irradiation with a particle beam, a beam parameter estimated based on a prescription and a beam parameter of an actually emitted particle beam do not always match. In particular, in irradiation with a particle beam at a high dose rate, the variation of the beam parameter is not negligible. Therefore, in the technology described in <CIT>, the collection efficiency of the dose monitor cannot be appropriately corrected, and it is difficult to accurately control a dose of a particle beam with which a subject is irradiated.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a particle therapy system, an irradiation control apparatus, and an irradiation control method capable of more accurately controlling a dose of a particle beam with which a subject is irradiated.

The present invention provides a particle therapy system and an irradiation control apparatus according to the appended claims. Preferred embodiments of the present invention are given in the dependent claims.

According to the present invention, it is possible to control a dose of a particle beam more accurately with which a subject is irradiated.

First, a particle therapy system and an irradiation control apparatus according to a first embodiment of the present disclosure will be described with reference to <FIG>.

<FIG> is a diagram illustrating an overall configuration of the particle therapy system according to the present embodiment. A particle therapy system <NUM> illustrated in <FIG> is a system that irradiates a patient <NUM> who is a subject with a beam <NUM> which is a particle beam. In the present embodiment, the particle therapy system <NUM> uses a spot scanning irradiation method or a raster scanning irradiation method in which spots which are a plurality of minute regions virtually set in the body of the patient <NUM> are sequentially irradiated.

As illustrated in <FIG>, the particle therapy system <NUM> includes an accelerator system <NUM>, a beam transport system <NUM>, an irradiation nozzle <NUM>, a couch <NUM>, a treatment planning apparatus <NUM>, an overall control apparatus <NUM>, an accelerator control apparatus <NUM>, and an irradiation control apparatus <NUM>.

The accelerator system <NUM> is an apparatus group that generates and extracts the beam <NUM>. In the example in <FIG>, the accelerator system <NUM> includes an ion source <NUM>, an injector <NUM>, and a synchrotron accelerator <NUM>. The ion source <NUM> generates charged particles that are particles constituting the beam <NUM>. The injector <NUM> injects the charged particles generated by the ion source <NUM> into the synchrotron accelerator <NUM>. The synchrotron accelerator <NUM> accelerates the charged particles injected from the injector <NUM> to generate and output the beam <NUM>.

Note that the accelerator system <NUM> illustrated in <FIG> is merely an example, and is not limited to this example. For example, the accelerator system <NUM> may be an apparatus group using a cyclotron accelerator or a synchrocyclotron accelerator instead of the synchrotron accelerator <NUM>.

The beam transport system <NUM> is an apparatus group that transports the beam <NUM> extracted from the accelerator system <NUM> to the irradiation nozzle <NUM>. The beam transport system <NUM> includes a beam path <NUM> and a bending magnet <NUM>. The beam path <NUM> is a path through which the beam <NUM> passes, and connects the accelerator system <NUM> and the irradiation nozzle <NUM>. The beam path <NUM> is in a vacuum state. The bending magnet <NUM> bends the beam passing through the beam path <NUM> by a magnetic field and transports the beam to the irradiation nozzle <NUM>. The beam transport system <NUM> may include or does not have to include a rotating gantry that adjusts an irradiation angle at which the patient <NUM> is irradiated with the beam <NUM>.

The irradiation nozzle <NUM> is an apparatus container including an apparatus group that includes an apparatus for irradiating the patient <NUM> with the beam <NUM> transported from the beam transport system <NUM> and an apparatus for measuring a beam parameter which is a parameter related to the beam <NUM>. A more detailed configuration of the irradiation nozzle <NUM> will be described below with reference to <FIG>.

The couch <NUM> is a bed on which the patient <NUM> is placed. The couch <NUM> changes the position and posture (angle) of the patient <NUM> to a desired position and posture by moving based on an instruction from the overall control apparatus <NUM>. The couch <NUM> can perform movement in six axial directions including, for example, translational movement along each of three different axes and rotational movement around each of the three axes.

The treatment planning apparatus <NUM> performs treatment planning for the patient <NUM>, creates a prescription, and transmits the prescription to the overall control apparatus <NUM>. The prescription indicates, for each spot irradiated with the beam <NUM>, a target dose which is a target value of a dose of the beam <NUM> with which each spot is irradiated.

The overall control apparatus <NUM> is connected to the couch <NUM>, the treatment planning apparatus <NUM>, the accelerator control apparatus <NUM>, and the irradiation control apparatus <NUM>, and controls each connected device based on the prescription from the treatment planning apparatus <NUM>.

The accelerator control apparatus <NUM> controls the accelerator system <NUM> and the beam transport system <NUM> based on an instruction from the overall control apparatus <NUM>.

The irradiation control apparatus <NUM> controls the irradiation nozzle <NUM> based on an instruction from the overall control apparatus <NUM>. Further, the irradiation control apparatus <NUM> processes a result of measurement using the irradiation nozzle <NUM> and transfers the processed result to the overall control apparatus <NUM>. A more detailed configuration of the irradiation control apparatus <NUM> will be described below with reference to <FIG>.

The treatment planning apparatus <NUM>, the overall control apparatus <NUM>, the accelerator control apparatus <NUM>, and the irradiation control apparatus <NUM> are implemented by, for example, a computer system including a central processing unit (CPU), a memory, a storage apparatus, a communication interface apparatus, a user interface (UI) apparatus, and the like. Each of these apparatuses performs various processings, for example, by the central processing unit reading and executing a program recorded in the memory. The program of each apparatus may be a single program, may be divided into a plurality of programs, or may be a combination thereof. Some or all of the programs may be implemented by dedicated hardware or may be modularized. In addition, some or all of the programs may be installed in each apparatus by using a program distribution server (not illustrated), an external storage medium, or the like. The apparatuses may each be implemented as an independent apparatus and may be connected to each other by a wired or wireless network, or two or more apparatuses may be integrated.

<FIG> is a diagram illustrating a configuration example of the irradiation nozzle <NUM>.

The irradiation nozzle <NUM> illustrated in <FIG> includes an irradiation system <NUM> for irradiating the patient <NUM> with the beam <NUM>, and a dose monitor control apparatus <NUM>, a position monitor control apparatus <NUM>, and a scanning magnet control apparatus <NUM> which are control systems that control the irradiation system <NUM>. The irradiation system <NUM> includes scanning magnets 201A and 201B, a dose monitor <NUM>, and a position monitor <NUM>.

Note that the irradiation system <NUM> may include a ridge filter <NUM> that enlarges a Bragg peak of the beam <NUM> in a traveling direction of the beam <NUM> and a range shifter <NUM> that adjusts a depth to be reached by the beam <NUM>, as necessary.

The scanning magnets 201A and 201B are scanning systems that scan the beam <NUM> in a plane (two-dimensional direction) orthogonal to a passing direction of the beam <NUM>. A target volume <NUM> in the patient <NUM> is irradiated with the beam <NUM> scanned by the scanning magnets 201A and 201B. The target volume <NUM> is an irradiation region irradiated with the beam <NUM>. For example, in a case where the particle therapy system <NUM> treats a tumor such as a cancer of the patient <NUM>, the target volume <NUM> is a region obtained by adding a margin (a margin region considering an error in an irradiation position) to a tumor region where the tumor is present. The spot irradiated with the beam <NUM> is set in the target volume <NUM>.

The dose monitor <NUM> is a monitor for measuring a dose rate of the beam <NUM> with which each spot is irradiated. The dose monitor <NUM> outputs a detection signal indicating a measurement result to the dose monitor control apparatus <NUM>. The dose monitor control apparatus <NUM> calculates the dose rate of the beam <NUM> with which each spot is irradiated based on the detection signal from the dose monitor <NUM>, and outputs the dose rate to the irradiation control apparatus <NUM>.

<FIG> is a diagram illustrating an example of the dose monitor <NUM>. The dose monitor <NUM> illustrated in <FIG> is a commonly used parallel plate ionization chamber.

The dose monitor <NUM> which is a parallel plate ionization chamber illustrated in <FIG> is covered with a shielding wall <NUM>, and a plurality of beam windows <NUM> having a high transmittance with respect to the beam <NUM> are formed in the shielding wall <NUM>. Specifically, the beam windows <NUM> are formed at positions facing each other in the shielding wall <NUM>, so that a beam <NUM> entering from one beam window <NUM> is extracted from the other beam window. In a space surrounded by the shielding wall <NUM>, one or more flat plate-shaped high-voltage electrodes <NUM> and one or more flat plate-shaped collector electrodes <NUM> are arranged in parallel. In the example in <FIG>, the dose monitor <NUM> includes one collector electrode <NUM> and two high-voltage electrodes <NUM> provided while having the collector electrode <NUM> interposed therebetween. A high voltage is fed to the high-voltage electrode <NUM>, and an electric field is generated between the high-voltage electrode <NUM> and the collector electrode <NUM>. In addition, a space between the respective electrodes <NUM> and <NUM> is filled with gas.

The beam <NUM> that has passed through the beam window <NUM> and has entered the dose monitor <NUM> ionizes the gas between the electrodes <NUM> and <NUM> to generate cations and electrons. The generated cations and electrons move to the collector electrode <NUM> by an electric field generated between the electrodes <NUM> and <NUM>. A current <NUM> flows between the electrodes <NUM> and <NUM> by the movement of the cations and electrons, and is measured by the dose monitor control apparatus <NUM>.

A proportional relationship is established between the dose of the beam <NUM> and the number of ions generated. Therefore, the dose monitor control apparatus <NUM> calculates the dose rate of the beam <NUM> based on the current <NUM> by multiplying the value of the current <NUM> by an appropriate coefficient. The dose rate calculated by the dose monitor control apparatus <NUM> is a dose rate before correction that is a dose rate that does not take into consideration a variation in collection efficiency of the dose monitor <NUM>.

The dose monitor <NUM> is not limited to the example illustrated in <FIG>. For example, the space between the electrodes <NUM> and <NUM> may be filled with liquid or opened to air. The shape of each of the electrodes <NUM> and <NUM> is not limited to the flat plate shape, and may be, for example, a coaxial cylindrical shape. The dose monitor <NUM> is not limited to the ionization chamber, and may be any monitor as long as a measurement characteristic changes according to the dose rate and the beam size.

The description returns to <FIG>. The position monitor <NUM> is a monitor for measuring the center position and the beam size of the beam <NUM>. The position monitor <NUM> outputs a detection signal indicating a measurement result to the position monitor control apparatus <NUM>. The position monitor control apparatus <NUM> calculates the center position and the beam size of each beam based on the detection signal input from the position monitor <NUM>, and outputs the center position and the beam size to the irradiation control apparatus <NUM>.

<FIG> is a diagram illustrating an example of the position monitor <NUM>. The position monitor <NUM> illustrated in <FIG> is a commonly used multi-strip ionization chamber.

Similarly to the dose monitor <NUM> illustrated in <FIG>, the multi-strip ionization chamber serving as the position monitor <NUM> is covered with a shielding wall (not illustrated), and a plurality of beam windows <NUM> having a high transmittance with respect to the beam <NUM> are formed in the shielding wall. Specifically, the beam windows <NUM> are formed at positions facing each other in the shielding wall, so that a beam <NUM> entering from one beam window <NUM> is extracted from the other beam window. In a space surrounded by the shielding wall, one or more flat plate-shaped high-voltage electrodes <NUM> and one or more flat plate-shaped collector electrodes 403A and 403B are arranged in parallel. A high voltage is fed to the high-voltage electrode <NUM>, and an electric field is generated between the high-voltage electrode <NUM> and the collector electrodes 403A and 403B. A space between the electrodes <NUM>, 403A, and 403B is filled with a fluid such as a gas or a liquid.

The collector electrode 403A is implemented by a plurality of strip-shaped small collector electrodes arranged in parallel in one direction (X direction) in the plane, and the collector electrode 403B is implemented a plurality of strip-shaped small collector electrodes arranged in parallel in a direction (Y direction) orthogonal to the X direction in the plane.

The beam <NUM> that has passed through the beam window <NUM> and has entered the position monitor <NUM> ionizes the fluid between the electrodes <NUM> and <NUM> to generate cations and electrons. The generated cations and electrons move to each small collector electrode of the collector electrode 403A or 403B in the vicinity by the electric field generated between the electrodes <NUM> and <NUM>, and a current <NUM> is generated by the movement of the cations and electrons and is measured for each small collector electrode by the position monitor control apparatus <NUM>. As a result, the position monitor control apparatus <NUM> can measure not only a two-dimensional ion generation distribution, but also a dose distribution in the in-plane direction of the collector electrode 403A or 403B based on the current <NUM> for each small collector electrode, and can calculate the center position and the beam size of the beam <NUM> based on the dose distribution.

<FIG> is a diagram for describing an example of a calculation method of calculating the center position and the beam size of the beam <NUM>. In <FIG>, the horizontal axis represents the center position of each small collector electrode of the collector electrode 403A in the X direction, and the vertical axis represents a current value. Each data point <NUM> in <FIG> represents a current value indicated by a detection signal of each small collector electrode.

Assuming that the shape of the beam <NUM> follows the Gaussian distribution, a peak position <NUM> and a standard deviation <NUM> when a distribution of the data point <NUM> is approximated by a Gaussian function <NUM> are the center position and the beam size of the beam <NUM>, respectively. Although <FIG> illustrates an example of a one-dimensional distribution for simplicity, actually, a two-dimensional dose distribution is approximated by a two-dimensional Gaussian function.

The method of calculating the center position and the beam size of the beam <NUM> is not limited to the above example, and the dose distribution may be approximated by a Lorentz function on the assumption that the shape of the beam <NUM> follows the Lorentz distribution. Furthermore, the position monitor <NUM> is not limited to the example illustrated in <FIG>. For example, the position monitor <NUM> may be a multi-wire ionization chamber or the like.

The description returns to <FIG>. The irradiation control apparatus <NUM> calculates the irradiation position of the beam <NUM> based on the center position of the beam <NUM> calculated by the position monitor control apparatus <NUM>. In addition, the irradiation control apparatus <NUM> calculates collection efficiency that is the measurement characteristic of the dose monitor <NUM> based on the beam parameters (the dose rate, the center position, and the beam size) transmitted from the dose monitor control apparatus <NUM> and the position monitor control apparatus <NUM>. The irradiation control apparatus <NUM> corrects the dose rate calculated by the dose monitor control apparatus <NUM> based on the collection efficiency to calculate a corrected dose rate in consideration of a variation in collection efficiency.

Next, an operation of the particle therapy system <NUM> will be described.

<FIG> is a flowchart for describing an example of treatment processing of treating the patient <NUM> by the particle therapy system <NUM>.

In the particle therapy, usually, the high-dose beam <NUM> is applied to the patient <NUM> at a time, and thus, in order to suppress a normal tissue of the patient <NUM> from being damaged, divided irradiation in which the patient <NUM> is dividedly irradiated with the beam a plurality of times is performed. In the present embodiment, a unit of division is one day, and the number of times the irradiation with the beam is dividedly performed is <NUM>. However, the unit of division and the number of times the irradiation with the beam is dividedly performed are not limited to these examples. For example, the unit of division does not need to be one day, and the treatment may be performed a plurality of times per day.

First, once a treatment on the day (d-th day) starts (Step S601), the treatment planning apparatus <NUM> creates a prescription as a treatment plan (Step S602). An initial value of d is <NUM>.

Specifically, in Step S602, the treatment planning apparatus <NUM> first reads an in-vivo image showing the periphery of a tumor that is a target volume of the patient <NUM>, and converts a thickness distribution from the body surface of the patient <NUM> to the target volume into a water equivalent thickness ratio distribution based on the in-vivo image. The in-vivo image is created by, for example, a computed tomography (CT) examination or the like. The water equivalent thickness ratio is a ratio of the thickness of water to the thickness of a local medium that causes the same energy loss for the beam <NUM> and is a physical quantity that determines a stopping distance of the beam <NUM>.

Subsequently, the treatment planning apparatus <NUM> uses the in-vivo image to determine a contour of the target volume <NUM>, which is a three-dimensional irradiation region irradiated with the beam <NUM>. For example, the treatment planning apparatus <NUM> displays the in-vivo image, causes an operator such as a doctor to draw a contour of a tumor, and determines the contour of the target volume <NUM> by giving a predetermined margin to the contour of the tumor.

Furthermore, the treatment planning apparatus <NUM> creates a prescription (a target dose set for each spot). Specifically, the treatment planning apparatus <NUM> first sets a target dose for the target volume <NUM>. The target dose is input by an operator, for example. The treatment planning apparatus <NUM> creates a prescription by calculating the position of a spot for applying the target dose to the target volume <NUM> and the target dose by using a predetermined optimization calculation method or the like based on the water equivalent thickness ratio distribution. The treatment planning apparatus <NUM> displays the prescription, and once the operator approves the prescription, the treatment planning apparatus <NUM> transmits the prescription to the overall control apparatus <NUM>.

The overall control apparatus <NUM> creates control instruction data for controlling the accelerator control apparatus <NUM> and the irradiation control apparatus <NUM> for each spot based on the prescription from the treatment planning apparatus <NUM>, and transmits the control instruction data to the accelerator control apparatus <NUM> and the irradiation control apparatus <NUM>. The transmitted data is stored in a memory (not illustrated) in the accelerator control apparatus <NUM> and the irradiation control apparatus <NUM>. Examples of the control instruction data for the accelerator control apparatus <NUM> include an excitation current value of each magnet of the accelerator system <NUM> and the beam transport system <NUM> determined according to beam energy corresponding to the depth of a spot position, a radio frequency power value fed to a radio frequency accelerating cavity, and the like. In addition, the control instruction data for the irradiation control apparatus <NUM> includes a target dose, current values of the scanning magnets 201A and 201B, and the like.

Then, the processing of Step S602 ends. In a case where the prescription is not approved by the operator, the target dose is reset.

Thereafter, the patient <NUM> is placed on the couch <NUM>, the position of the patient <NUM> is adjusted in such a way as to match with that at the time of capturing the in-vivo image, and the operator instructs the particle therapy system <NUM> to perform irradiation with the beam <NUM> (Step S603).

Then, the overall control apparatus <NUM> transmits an irradiation start instruction for a spot to be irradiated (referred to as the n-th spot) to the accelerator control apparatus <NUM> and the irradiation control apparatus <NUM> (Step S604). An initial value of n is <NUM>.

Once the irradiation start instruction is received, the accelerator control apparatus <NUM> starts acceleration of the beam <NUM> according to the control instruction data stored in the memory. Once the acceleration of the beam <NUM> is completed, the irradiation control apparatus <NUM> changes the current values of the scanning magnets 201A and 201B via the scanning magnet control apparatus <NUM>. Once the change of the current values is completed, the accelerator control apparatus <NUM> extracts the beam <NUM>. The extracted beam <NUM> passes through the beam transport system <NUM> and the irradiation nozzle <NUM> to irradiate the target volume <NUM> of the patient <NUM>. The dose monitor <NUM> and the position monitor <NUM> measure the beam parameters of the beam <NUM>, and the irradiation control apparatus <NUM> calculates the dose of the beam <NUM> for the n-th spot based on the beam parameters (Step S605).

Thereafter, once the dose reaches the target dose, the irradiation control apparatus <NUM> transmits an end signal indicating the end of irradiation of the n-th spot with the beam <NUM> to the overall control apparatus <NUM>. Once the end signal is received, the overall control apparatus <NUM> performs end processing which is processing of ending the irradiation of the n-th spot with the beam <NUM> (Step S606). The end processing is processing of stopping the irradiation with the beam <NUM> in a case where the spot scanning irradiation method in which movement between spots is performed in a state where the beam is stopped is adopted, and is processing of proceeding to irradiation preparation for the next spot in a case where the raster scanning irradiation method in which movement between spots is performed in a state where irradiation with the beam is performed is adopted.

Then, the overall control apparatus <NUM> determines whether or not irradiation of the last spot with the beam <NUM> has ended (Step S607).

In a case where the irradiation of the last spot with the beam <NUM> has not ended, the overall control apparatus <NUM> increments n, instructs the accelerator control apparatus <NUM> and the irradiation control apparatus <NUM> to prepare irradiation of the next spot (Step S608), and returns to the processing of Step S604.

On the other hand, in a case where the irradiation of the last spot with the beam <NUM> has ended, the treatment on the day ends. Then, the overall control apparatus <NUM> determines whether or not the day is the last day. In a case where the day is not the last day, the processing of Step S601 is performed, and in a case where the day is the last day, the processing ends.

The irradiation control apparatus <NUM> may be directly connected to the accelerator control apparatus <NUM> and directly transmit various signals to the accelerator control apparatus <NUM>.

Hereinafter, irradiation dose monitoring processing which corresponds to the processings of Steps S604 to S606 of <FIG>, will be described in more detail.

<FIG> is a diagram illustrating a configuration example of an irradiation control system including the irradiation nozzle <NUM> and the irradiation control apparatus <NUM>. <FIG> is a flowchart for describing an example of monitoring processing performed by the irradiation control system illustrated in <FIG>. Hereinafter, the irradiation of the n-th spot with the beam <NUM> will be described as an example.

As illustrated in <FIG>, the dose monitor control apparatus <NUM> includes an I/F converter <NUM> that converts a current output from the dose monitor <NUM> into a pulse signal, and a CPU <NUM> that calculates a dose rate based on the pulse signal obtained by the conversion performed by the I/F converter <NUM>. A pulse frequency of the pulse signal represents the dose rate. The position monitor control apparatus <NUM> includes an I/F converter <NUM> that converts a current output from the position monitor <NUM> into a pulse signal, and a CPU <NUM> that calculates the center position and the beam size of the beam <NUM> based on the pulse signal obtained by the conversion performed by the I/F converter <NUM>.

The irradiation control apparatus includes a memory <NUM> that stores the control instruction data (the target dose for each spot) and a CPU <NUM>. The CPU <NUM> includes a counter <NUM> that counts the number of pulses.

Once Step S604 starts, the overall control apparatus <NUM> first transmits an irradiation start instruction to the accelerator control apparatus <NUM> and the irradiation control apparatus <NUM> (Step S801). Once the irradiation start instruction is received, the accelerator control apparatus <NUM> accelerates and extracts the beam <NUM> according to the control instruction data stored in the memory (Step S803).

The CPU <NUM> of the irradiation control apparatus <NUM> reads the target dose corresponding to the n-th spot among the target doses stored in the memory <NUM> in Step S602 during a period from the reception of the irradiation start instruction to the extraction of the beam <NUM> by the accelerator control apparatus <NUM> (between Steps S801 and S803). In the present embodiment, a current output from the dose monitor <NUM> is converted into a pulse signal by the I/F converter <NUM> of the dose monitor control apparatus <NUM>, and the number of pulses of the pulse signal represents the dose. Therefore, the CPU <NUM> sets the target number of pulses in the counter <NUM>, the target number of pulses being obtained by converting the target dose into the number of pulses (Step S802).

A conversion count for converting the target dose into the target number of pulses is determined according to a characteristic of a dose measurement circuit including the dose monitor <NUM> and the I/F converter <NUM>. The processing of Step S802 may be performed during a period from the end of irradiation of the previous spot ((n-<NUM>)-th spot) with the beam <NUM> to transmission of the irradiation start instruction for a corresponding spot.

Once the beam <NUM> is extracted (Step S803), the currents detected by the dose monitor <NUM> and the position monitor <NUM> during the irradiation of the target volume <NUM> with the beam <NUM> are converted into pulse signals by the I/F converters <NUM> and <NUM> in the dose monitor control apparatus <NUM> and the position monitor control apparatus <NUM>, respectively. As described with reference to <FIG>, the CPU <NUM> of the dose monitor control apparatus <NUM> calculates the dose rate of the beam <NUM> based on the pulse signal and transmits the dose rate to the irradiation control apparatus <NUM>. In addition, as described with reference to <FIG>, the CPU <NUM> of the position monitor control apparatus <NUM> calculates the center position and the beam size of the beam <NUM> based on a two-dimensional distribution of the pulse frequency of the pulse signal, and transmits the center position and the beam size to the irradiation control apparatus <NUM> (Step S804). Similarly to the conversion coefficient for the target dose, a conversion coefficient for converting a current into a pulse signal is a constant determined according to the characteristic of the dose measurement circuit.

The CPU <NUM> of the irradiation control apparatus <NUM> calculates the collection efficiency of the dose monitor <NUM> for the beam <NUM> based on the dose rate and the beam size (Step S805).

Hereinafter, a calculation method based on a theoretical formula will be described as an example of a collection efficiency calculation method.

Assuming that a spread of the beam <NUM> follows the Gaussian distribution, a beam current density i(r) of the beam <NUM> at a distance r from the center of the beam <NUM> is expressed by the following Formula <NUM> using an actual integral beam current I of the beam <NUM> and a beam size σ. The distance r is a distance in an in-plane direction orthogonal to the traveling direction of the beam <NUM>. <NUM> <MAT>.

Meanwhile, an integral beam current J measured by the dose monitor <NUM> is expressed by the following Formula <NUM> using the beam current density i(r) and local collection efficiency f(r) in a minute region in the dose monitor <NUM>. <NUM> <MAT>.

According to Boag's theory, the local collection efficiency f(r) and the beam current density i(r) have a relationship represented by Formula <NUM>. <NUM> <MAT>.

Here, k is <NUM> × <NUM><NUM> [V/ (m<NUM>A<NUM>)], V is a fed voltage to be fed to the dose monitor <NUM>, and d is a constant determined according to the structure of the dose monitor <NUM>. For example, in a case where the dose monitor <NUM> includes one high-voltage electrode <NUM> and one collector electrode <NUM>, d is an interval between the high-voltage electrode <NUM> and the collector electrode <NUM>. By substituting Formulae <NUM> and <NUM> into Formula <NUM> and integrating Formula <NUM>, collection efficiency F of the entire dose monitor <NUM> is expressed by Formula <NUM> as a function of the integral beam current J. <NUM> <MAT>.

The integral beam current J is obtained by integrating a constant coefficient with the dose rate calculated by the dose monitor control apparatus <NUM>, and the beam size σ is calculated by the position monitor control apparatus <NUM>. Therefore, the CPU <NUM> of the irradiation control apparatus <NUM> can calculate the collection efficiency F by substituting these values into Formula <NUM>.

The collection efficiency calculation method described above is merely an example, and is not limited to this method. For example, although it has been assumed above that the spread of the beam <NUM> follows the Gaussian distribution, in a case where the spread of the beam <NUM> is a distribution defined according to the integral beam current and the beam size, it may be assumed that the spread of the beam <NUM> follows the Lorentz distribution or the like.

In addition, for example, a method using a collection efficiency table indicating a relationship between the dose rate, the beam size σ, and the collection efficiency may be used instead of the method of calculating the collection efficiency by using Formula (<NUM>) that is a theoretical formula. In this method, the CPU <NUM> of the irradiation control apparatus <NUM> calculates the collection efficiency by referring to the collection efficiency table created in advance.

<FIG> is a diagram illustrating an example of the collection efficiency table. A collection efficiency table <NUM> illustrated in <FIG> is a matrix table in which the row corresponds to the dose rate and the column corresponds to the beam size, and each element represents the collection efficiency for the dose rate and the beam size corresponding to its row and column.

Examples of a method of creating the collection efficiency table include a method in which measurement is performed by the dose monitor <NUM> on a beam whose dose rate and beam size are known, and processing of calculating the collection efficiency by comparing an ideal dose rate with the measured dose rate is repeatedly performed while changing the dose rate and the beam size.

The description returns to the operation in <FIG> and <FIG>. Once the processing of Step S805 ends, the CPU <NUM> of the irradiation control apparatus <NUM> multiplies the pulse frequency of the pulse signal from the dose monitor control apparatus <NUM> by a reciprocal of the collection efficiency to acquire a corrected pulse frequency corresponding to a corrected dose rate that is a dose rate that takes into consideration a variation in collection efficiency. The CPU <NUM> counts the corrected number of pulses corresponding to the corrected dose obtained by correcting the measured dose obtained by measuring the dose applied to the n-th spot with the collection efficiency, by integrating the corrected pulse frequency using the counter <NUM> (Step S806).

The CPU <NUM> of the irradiation control apparatus <NUM> determines whether or not the corrected dose has reached the target dose by determining whether or not the corrected number of pulses has reached the target number of pulses read from the memory <NUM> (Step S807). In a case where the corrected dose has not reached the target dose, the processing of Step S804 is performed again, and in a case where the corrected dose has reached the target dose, the irradiation dose monitoring processing ends, and the processing of Step S606 in <FIG> is performed.

Next, effects of the present embodiment will be described.

According to the present embodiment, the dose monitor <NUM> measures the dose of the beam <NUM>. The position monitor <NUM> measures the beam size of the beam <NUM>. The irradiation control apparatus <NUM> calculates the measurement characteristic of the dose monitor <NUM> based on the dose and the beam size of the beam <NUM>, and controls the irradiation of the patient <NUM> with the beam <NUM> based on the measurement characteristic and the dose. Accordingly, since the irradiation of the patient <NUM> with the beam <NUM> is controlled based on the measurement characteristic of the dose monitor <NUM> calculated based on the actually measured dose and beam size of the beam <NUM>, it is possible to control the dose of the beam <NUM> more accurately with which the patient <NUM> is irradiated.

Furthermore, in the present embodiment, the irradiation control apparatus <NUM> calculates a corrected dose obtained by correcting the dose based on the measurement characteristic, and performs processing of ending the irradiation with the beam <NUM> in a case where an integral value of the corrected dose has reached the target dose. It is sufficient if the setting of the target dose and the like is performed in the same manner as in the related art except for correcting the dose. Therefore, it is not necessary to change a processing system, that is, it is not necessary to add and change an existing hardware apparatus, and it is possible to prevent an additional cost from being incurred.

In the present embodiment, the collection efficiency of the ionization chamber is used as the measurement characteristic of the dose monitor <NUM>. Therefore, the general dose monitor <NUM> can be used, and it is thus possible to prevent an additional cost from being incurred.

Next, a particle therapy system and an irradiation control apparatus according to a second embodiment of the present disclosure will be described with reference to <FIG>. Hereinafter, differences from the first embodiment will be mainly described. The same components as those in the first embodiment are denoted by the same reference signs.

An overall configuration of a particle therapy system <NUM> according to the second embodiment is similar to the overall configuration of the particle therapy system <NUM> according to the first embodiment illustrated in <FIG>. However, in the present embodiment, an irradiation control apparatus <NUM> calculates a corrected target dose obtained by correcting a target dose instead of correcting a dose based on collection efficiency of a dose monitor <NUM>. In a case where an integral value of the dose measured by the dose monitor <NUM> has reached the corrected target dose, the irradiation control apparatus <NUM> performs end processing of ending irradiation with a beam <NUM>. The corrected target dose is calculated for each spot, and the collection efficiency used to calculate the corrected target dose for each spot is calculated based on the dose and a beam size of the beam <NUM> with which a reference spot, which is a previous irradiated spot, has been irradiated. In the present embodiment, the collection efficiency for each spot is calculated based on the dose and the beam size of the beam <NUM> with which a previous irradiated spot has been irradiated.

In a case where a difference in characteristic of the beam <NUM> with respect to each of the reference spot and the irradiation spot is sufficiently small, the collection efficiency is calculated with high accuracy also in the present embodiment, and highly accurate irradiation control can be performed. For example, in a case where a periodic variation scale of a beam parameter is longer than an irradiation time for one spot and a difference in beam parameter between adjacent spots is smaller than a difference between an irradiation instruction and actual irradiation, it is possible to calculate the collection efficiency with higher accuracy than that in a case of calculating the collection efficiency based on a prescription, by referring to an average value of the beam parameters for the immediately previous spot.

The overall flow of treatment processing of treating a patient <NUM> in the present embodiment is similar to the overall flow of the treatment processing described with reference to <FIG>. However, since the dose and the beam size of the beam <NUM> for calculating the corrected target dose cannot be obtained for the first spot irradiated with the beam <NUM> first, the irradiation control apparatus <NUM> performs additional processing for reducing an influence of an error of the dose applied to the first spot on treatment quality at the time of creating a prescription in Step S602.

The additional processing is processing of determining, as the first spot, a spot satisfying a predetermined condition among a plurality of spots obtained by dividing a target volume <NUM>. For example, in the additional processing, the first spot is determined based on the target volume <NUM>.

<FIG> is a diagram illustrating an example of the first spot. The example in <FIG> is an example in which the first spot is set to a spot <NUM> closest to the center of the target volume <NUM>. In this case, since it is considered that there is no or few normal tissues in the vicinity of the spot <NUM>, the influence of the error of the dose on the treatment quality can be reduced.

The first spot illustrated in <FIG> is merely an example, and the first spot is not limited thereto. For example, the first spot may be a spot whose distance from a predetermined organ is a certain value or more. In addition, the first spot set by an arbitrary method may be divided into a plurality of subdivided spots, and any of the subdivided spots may be reset as the first spot. In this case, the target dose for the subdivided spot can be reduced, and thus, the dose applied to the subdivided spot can be reduced. As a result, the influence of the error of the dose on the treatment quality can be reduced.

The additional processing may be automated by a program of the irradiation control apparatus <NUM>, or may be processing of displaying the target volume <NUM> and each spot to make an operator perform selection.

Hereinafter, irradiation dose monitoring processing according to the second embodiment (processings of Steps S604 to S606 of <FIG>) will be described in more detail.

<FIG> is a diagram illustrating a configuration example of an irradiation control system including an irradiation nozzle <NUM> and the irradiation control apparatus <NUM>. <FIG> is a flowchart for describing an example of monitoring processing performed by the irradiation control system illustrated in <FIG>. Hereinafter, irradiation of the n-th spot with the beam <NUM> will be described as an example.

After starting the irradiation of the n-th spot, an overall control apparatus <NUM> transmits an irradiation start instruction to an accelerator control apparatus <NUM> and the irradiation control apparatus <NUM> (Step S1201). Once the irradiation start instruction is received, the accelerator control apparatus <NUM> accelerates and extracts the beam <NUM> according to control instruction data stored in a memory (Step S1204).

A CPU <NUM> of the irradiation control apparatus <NUM> performs the following Steps S1202 and S1203 during a period from the reception of the irradiation start instruction to the extraction of the beam <NUM> by the accelerator control apparatus <NUM>.

First, the CPU <NUM> calculates the collection efficiency of the dose monitor <NUM> based on an average dose rate and an average size of the beam <NUM> with which the immediately previous spot ((n-<NUM>)-th spot) stored in a memory <NUM> is irradiated (Step S1202). The average dose rate is an average value of the dose rates of the beam <NUM> with which the immediately previous spot is irradiated, and the average size is an average value of the beam sizes of the beam <NUM> with which the immediately previous spot is irradiated. The average dose rate is an average value of dose rates that have not been corrected based on the collection efficiency. Similarly to the first embodiment, the collection efficiency may be calculated by a method using Theoretical Formula (<NUM>) or a method using the table as illustrated in <FIG>.

In a case where n = <NUM>, that is, in a case where the first spot is irradiated with the beam <NUM>, there is no average dose rate and average size corresponding to the immediately previous spot. Therefore, the CPU <NUM> may set a fixed value (for example, <NUM>) as the collection efficiency, or may approximate the collection efficiency based on the average dose rate and the average size estimated based on a prescription.

Next, the CPU <NUM> reads the target dose for the n-th spot from the memory <NUM>, and calculates a corrected target dose obtained by correcting the target dose based on the collection efficiency. The CPU <NUM> sets the target number of pulses in a counter <NUM>, the target number of pulses being obtained by converting the corrected target dose into the number of pulses (Step S1203).

Once the beam <NUM> is extracted (Step S1204), currents detected by the dose monitor <NUM> and a position monitor <NUM> during the irradiation of the target volume <NUM> with the beam <NUM> are converted into pulse signals by I/F converters <NUM> and <NUM> in a dose monitor control apparatus <NUM> and a position monitor control apparatus <NUM>, respectively, and the pulse signals are output. The CPU <NUM> of the irradiation control apparatus <NUM> transmits the pulse signal output from the I/F converter <NUM> to the counter <NUM> to integrate the number of pulses. That is, in the present embodiment, unlike the first embodiment, the dose rate is not corrected based on the collection efficiency. In addition, a CPU <NUM> of the position monitor control apparatus <NUM> calculates a center position and the beam size of the beam <NUM> based on the pulse signal output from the I/F converter <NUM> (Step S1205).

The CPU <NUM> of the irradiation control apparatus <NUM> determines whether or not the dose applied to the n-th spot has reached the corrected target dose by determining whether or not the integrated number of pulses has reached the corrected target number of pulses for the n-th spot read from the memory <NUM> (Step S1206).

In a case where the dose has not reached the corrected target dose, the processing returns to Step S1205. On the other hand, in a case where the dose has reached the corrected target dose, a CPU <NUM> of the dose monitor control apparatus <NUM> calculates, as an average dose rate before correction, an average value of the dose rates of the beam <NUM> with which the first spot is irradiated, and records the average value in the memory <NUM> of the irradiation control apparatus <NUM>. In addition, the CPU <NUM> of the position monitor control apparatus <NUM> calculates, as an average size, an average value of the beam sizes of the beam <NUM> with which the first spot is irradiated, records the average value in the memory <NUM> of the irradiation control apparatus <NUM> (Step S1207), and ends the processing. The average dose rate before correction and the average size may be collectively referred to as an average irradiation parameter. In addition, the average dose rate before correction is a name for convenience, and in the present embodiment, the dose rate is not corrected.

In the above operation, a timing for calculating the average irradiation parameter and the collection efficiency is not limited to the timing described with reference to <FIG>. For example, the average irradiation parameter may be calculated based on the number of pulses integrated up to a predetermined time point before the irradiation with the beam <NUM> ends, or the collection efficiency may be calculated during a period from a timing at which the irradiation with the beam <NUM> ends to a timing at which irradiation of the next spot starts.

In the above example, the reference spot refers to the immediately previous spot of a target spot, but the reference spot is not limited to this example. For example, the irradiation control apparatus <NUM> may select, as the reference spot, a spot at which the beam parameter is closest to the beam <NUM> with which the target spot is irradiated based on a variation trend of the beam parameter of the beam <NUM>.

As described above, according to the present embodiment, the irradiation control apparatus <NUM> calculates a corrected target dose obtained by correcting a predetermined target dose based on a measurement characteristic, and performs processing of ending irradiation with the beam <NUM> in a case where an integral value of the dose has reached the corrected target dose. Therefore, similarly to the first embodiment, it is possible to set the target dose in the same manner as in the related art, and thus, it is not necessary to change the processing system. Therefore, it is not necessary to add or change an existing hardware apparatus, and it is possible to prevent an additional cost from being incurred.

In addition, in the present embodiment, the irradiation control apparatus <NUM> calculates the corrected target dose for each spot based on the dose and the beam size of the beam <NUM> with which a previous irradiated spot has been irradiated. Accordingly, since it is not necessary to correct the dose of the beam <NUM> in real time, it is possible to suppress occurrence of a delay in determination to end the irradiation with the beam <NUM> due to a processing time for the correction, and it is possible to suppress excessive irradiation.

In addition, in the present embodiment, the irradiation control apparatus <NUM> calculates the corrected target dose for each spot based on the dose and the beam size of the beam <NUM> with which the immediately previous spot of the corresponding spot is irradiated. Therefore, it is possible to calculate the corrected target dose based on the dose and the beam size of the beam <NUM> considered to be closest to the characteristics of the beam <NUM>, and thus, it is possible to control the dose of the beam <NUM> more accurately with which the patient <NUM> is irradiated.

Furthermore, in the present embodiment, a spot satisfying a predetermined condition is set as the first spot to be irradiated with the beam <NUM> first. Therefore, it is possible to reduce the influence of the error of an irradiation dose for the first spot on the treatment quality.

Claim 1:
A particle therapy system (<NUM>) that irradiates a subject (<NUM>) with a particle beam (<NUM>), the particle therapy system (<NUM>) comprising:
a dose monitor (<NUM>) that measures a dose of the particle beam (<NUM>);
a position monitor (<NUM>) that measures a beam size of the particle beam (<NUM>); and
an irradiation control apparatus (<NUM>) that calculates a measurement characteristic of the dose monitor (<NUM>) based on the dose and the beam size, and controls irradiation of the subject (<NUM>) with the particle beam (<NUM>) based on the measurement characteristic and the dose, wherein
the irradiation control apparatus (<NUM>) calculates a corrected dose obtained by correcting the dose based on the measurement characteristic, and performs processing of ending the irradiation with the beam (<NUM>) in a case where an integral value of the corrected dose has reached the target dose, or wherein
the irradiation control apparatus (<NUM>) calculates a corrected target dose obtained by correcting a predetermined target dose based on the measurement characteristic, and performs processing of ending the irradiation with the particle beam (<NUM>) in a case where an integral value of the dose has reached the corrected target dose.