Measurement device, measurement method, measurement system, and radiation therapy system

Abstract

This measuring device calculates the dose of gamma rays on the basis of the measured value of radiation including neutron rays and gamma rays measured in an ionization chamber including air and the detected value of neutron rays detected by a detector.

Description

[Technical Field]

[0001] The present disclosure relates to a measurement device, a measurement method, a measurement system, and a radiation therapy system. [Background technology]

[0002] In recent years, there has been a technology for treating cancer using neutron beams. For example, boron neutron capture therapy (BNCT) using boron compounds is known as a neutron capture therapy that kills cancer cells by irradiating them with neutron beams. In boron neutron capture therapy, boron that has been incorporated into cancer cells in advance is irradiated with neutron beams, and the resulting scattering of heavy charged particles selectively destroys the cancer cells.

[0003] In order to measure the amount of neutron radiation used in treatment in this way, for example, a neutron radiation measurement device is used, as shown in Patent Document 1. The neutron radiation measurement device shown in Patent Document 1 detects neutron radiation with a detection unit and calculates the amount of neutron radiation based on the detection result. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-166777 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, when neutron beams are generated from charged particle beams in neutron capture therapy, gamma rays are also generated. To ensure the quality of the beam irradiated in neutron capture therapy, it is necessary to properly measure not only the neutron beam dose but also the gamma ray dose. Conventional gamma ray measurement methods measure gamma rays using, for example, an ionization chamber filled with two types of gases with different sensitivities. However, this measurement method requires equipment for filling the ionization chamber with gas, which complicates the measurement process and increases the labor required. Therefore, there has been a demand for an easy way to measure gamma ray dose.

[0006] Therefore, an object of the present disclosure is to provide a measurement device, a measurement method, a measurement system, and a radiation therapy system that can easily measure the dose of gamma rays. [Means for solving the problem]

[0007] A measurement device according to one aspect of the present disclosure calculates the dose of gamma rays based on measurement values ​​of radiation including neutron rays and gamma rays measured in an ionization chamber containing air, and detection values ​​of neutron rays detected in a detector.

[0008] This measuring device calculates the dose of gamma rays based on the measured value of radiation measured in the ionization chamber and the detected value detected in the detector. Since the measured value is measured in an ionization chamber containing air, it can be easily measured without the need for additional equipment for filling the ionization chamber with gas. Furthermore, the measuring device can eliminate the influence of the value related to neutron rays from the measured value by using neutron counting. As described above, this measuring device can easily measure the dose of gamma rays. Furthermore, this measuring device can easily measure the dose of neutron rays as well.

[0009] In one embodiment, the measured values ​​include a first ionization amount due to a reaction between the air in the ionization chamber and the neutron radiation and a second ionization amount due to a reaction between the air in the ionization chamber and the gamma radiation, and the dose of gamma radiation is calculated based on the second ionization amount. In this case, the second ionization amount is derived based on the measured values, the first ionization amount, and the neutron count, and the dose of gamma radiation can be appropriately measured.

[0010] In one embodiment, the detected value is a neutron count related to the neutron beam, and the first ionization amount is approximated to the amount of ionization resulting from the reaction between the neutron beam and nitrogen contained in the air inside the ionization chamber. In this case, the amount of ionization resulting from the reaction between the nitrogen and the neutron beam is proportional to the neutron count, and therefore the first ionization amount can be considered to be proportional to the neutron count. Therefore, the first ionization amount is calculated based on the neutron count. Therefore, the second ionization amount can be derived by subtracting the first ionization amount from the measured value, and the dose of gamma rays can be appropriately measured.

[0011] A measurement method according to another aspect of the present disclosure includes a step of calculating a dose of gamma rays based on measured values ​​of radiation including neutron rays and gamma rays measured in an ionization chamber containing air, and detected values ​​of neutron rays detected in a detector.

[0012] According to this measurement method, it is possible to obtain the same functions and effects as those of the above-mentioned measurement device.

[0013] A measurement system according to another aspect of the present disclosure includes a radiation therapy device that irradiates radiation including neutron rays and gamma rays, and a measurement device that calculates the dose of gamma rays irradiated from the radiation therapy device based on measurement values ​​of radiation measured in an ionization chamber containing air and detection values ​​of neutron rays detected in a detector.

[0014] According to this measurement system, the measurement device calculates the dose of gamma rays based on measured values ​​of radiation irradiated from a radiotherapy device and detected values ​​of neutron rays irradiated from the radiotherapy device. Because the measured values ​​are measured in an ionization chamber containing air, they can be easily measured without the need for additional equipment for filling the ionization chamber with gas. Furthermore, the measurement device can eliminate the influence of values ​​related to neutron rays from the measured values ​​by using neutron counting. As described above, this measurement system can easily measure the dose of gamma rays from a radiotherapy device using the measurement device. Furthermore, this measurement system can easily measure the dose of neutron rays from a radiotherapy device using the measurement device.

[0015] A radiation therapy system according to another aspect of the present disclosure includes a radiation therapy device that irradiates radiation including neutron rays and gamma rays, and a measurement device that calculates the dose of gamma rays based on measurement values ​​of radiation measured in an ionization chamber containing air and detection values ​​of neutron rays detected by a detector, and the radiation therapy device controls the irradiation of radiation using the dose of gamma rays calculated by the measurement device.

[0016] According to this radiation therapy system, the measuring device calculates the dose of gamma rays based on measured values ​​of radiation irradiated from the radiation therapy device and detected values ​​of neutron rays irradiated from the radiation therapy device. Because the measured values ​​are measured in an ionization chamber containing air, they can be easily measured without the need for additional equipment for filling the ionization chamber with gas. Furthermore, the measuring device can eliminate the influence of values ​​related to neutron rays from the measured values ​​by using neutron counting. Therefore, the measuring device easily measures the dose of gamma rays from the radiation therapy device. Furthermore, the measuring device easily measures the dose of neutron rays from the radiation therapy device. The radiation therapy device can irradiate a patient with an appropriate dose of radiation by controlling the irradiation of radiation including neutron rays and gamma rays using at least one of the dose of neutron rays and the dose of gamma rays measured by the measuring device. Furthermore, the radiation therapy device can suppress irradiation of a patient with radiation including at least one of neutron rays and gamma rays having a dose exceeding a predetermined threshold. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide a measurement device, a measurement method, a measurement system, and a radiation therapy system that can easily measure the dose of gamma rays. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing a neutron capture therapy device as an example of a radiation therapy device according to an embodiment. [Figure 2] FIG. 1 is a block diagram of a measurement system and a measurement device according to an embodiment. [Figure 3] 10B is a graph showing the characteristics of the 10B. [Figure 4] 1 is a graph showing the characteristics of 6Li. [Figure 5] 1 is a graph showing the characteristics of 197Au. [Figure 6] 10 is a flowchart showing the processing steps of a neutron beam measurement method. [Figure 7]FIG. 10 is a block diagram of a measurement system and a measurement device according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments of the present disclosure will now be described in detail with reference to the drawings.

[0020] A measurement system according to an embodiment of the present disclosure includes a radiotherapy device and a measurement device. The measurement device calculates the dose of gamma rays. The measurement device calculates, for example, the dose of neutron rays and gamma rays irradiated by the radiotherapy device. The radiotherapy device is, for example, a neutron capture therapy device. First, with reference to FIG. 1, an overview of the neutron capture therapy device that generates neutron rays and gamma rays to be measured by the measurement device will be described. FIG. 1 is a schematic diagram showing a neutron capture therapy device, which is an example of a radiotherapy device. The neutron capture therapy device 1 (an example of a radiotherapy device) shown in FIG. 1 is a device that performs cancer treatment using boron neutron capture therapy (BNCT). The neutron capture therapy device 1 irradiates a patient 16 (irradiated body) with a charged particle beam P (an example of radiation) including neutron beam N and gamma rays G. The neutron capture therapy device 1 irradiates, for example, boron ( 10 B) The tumor of patient 16, who had been administered the drug, was irradiated with neutrons.

[0021] The neutron capture therapy device 1 includes an accelerator 2. The accelerator 2 accelerates charged particles such as anions and emits a charged particle beam P. The accelerator 2 is configured by, for example, a cyclotron. In this embodiment, the charged particle beam P is a proton beam generated by stripping charge from anions. The accelerator 2 generates, for example, a charged particle beam P with a beam radius of 40 mm and 60 kW (= 30 MeV × 2 mA). Note that the accelerator is not limited to a cyclotron, and may be a synchrotron, synchrocyclotron, linac, electrostatic accelerator, or the like.

[0022] The charged particle beam P extracted from the accelerator 2 is sent to a neutron beam generation unit M provided in the neutron capture therapy device 1. The neutron beam generation unit M is composed of a beam duct 9 and a target 10. The charged particle beam P extracted from the accelerator 2 passes through the beam duct 9 and travels toward the target 10 arranged at the end of the beam duct 9. A plurality of quadrupole electromagnets 4 and a scanning electromagnet 6 are provided along this beam duct 9. The multiple quadrupole electromagnets 4 adjust the beam axis of the charged particle beam P using, for example, electromagnets.

[0023] The scanning electromagnet 6 scans the charged particle beam P and controls the irradiation of the charged particle beam P onto the target 10. The scanning electromagnet 6 controls the irradiation position of the charged particle beam P on the target 10.

[0024] The neutron capture therapy device 1 generates a neutron beam N by irradiating a target 10 with a charged particle beam P, and emits the neutron beam N toward a patient 16 placed on a treatment table 17. The neutron capture therapy device 1 includes the target 10, a shield 8, a moderator 12, a collimator 14, and an irradiation control unit 18.

[0025] The target 10 generates radiation including neutron rays N and gamma rays G when irradiated with a charged particle beam P. Gamma rays G are generated in conjunction with the generation of the neutron beam N. The target 10 is a solid member formed from a material that generates neutron rays and gamma rays when irradiated with a charged particle beam. Specifically, the target 10 is formed from, for example, beryllium (Be), lithium (Li), tantalum (Ta), or tungsten (W), and has a disk-like solid shape with a diameter of, for example, 160 mm. Note that the target 10 is not limited to a disk shape and may have other shapes.

[0026] The moderator 12 moderates (reduces the energy of) the neutron beam N generated in the target 10. The moderator 12 may have a laminated structure made up of a layer 12A that mainly moderates fast neutrons contained in the neutron beam N and a layer 12B that mainly moderates epithermal neutrons contained in the neutron beam N.

[0027] The shielding body 8 shields the generated neutron rays N, gamma rays G, etc. from being released to the outside. The shielding body 8 is provided to surround the moderator 12. The upper and lower portions of the shielding body 8 extend upstream of the moderator 12 in the direction of the charged particle beam P.

[0028] The collimator 14 shapes the irradiation field of the neutron beam N, and has an opening 14a through which the neutron beam N passes. The collimator 14 is, for example, a block-shaped member having the opening 14a in the center.

[0029] The irradiation control unit 18 controls the irradiation of the charged particle beam P. The irradiation control unit 18 controls the irradiation of the charged particle beam P (radiation) including neutron rays and gamma rays using the gamma ray dose calculated by a measuring device described later. The irradiation control unit 18 controls, for example, the dose of the charged particle beam P irradiated from the accelerator 2. This will be described in detail later.

[0030] Next, a detailed configuration of a measurement device included in the measurement system will be described with reference to Fig. 2. Fig. 2 is a block diagram of a measurement system and a measurement device according to an embodiment. As shown in Fig. 2, a measurement system 200 (an example of a measurement system and a radiation therapy system) includes a neutron capture therapy device 1 and a measurement device 100. The measurement device 100 is a measurement device that calculates the dose (quantity) of gamma rays G generated by irradiating a target 10 with a charged particle beam P in the neutron capture therapy device 1. The measurement device 100 also calculates, for example, the dose (quantity) of neutron beam N generated by irradiating a target 10 with the charged particle beam P in the neutron capture therapy device 1. Note that the measurement device 100 in the measurement system 200 calculates, for example, each dose of the neutron beam N and the gamma rays G emitted from an opening 14a of a collimator 14 of the neutron capture therapy device 1. The measuring device 100 is provided downstream of the neutron beam N from the opening 14a of the collimator 14, for example, in a state where the patient 16 is not present on the examination table 17.

[0031] The measuring device 100 outputs, for example, the doses or measurement results of the gamma rays G and neutron rays N generated in the neutron capture therapy device 1 to the memory unit 50 or the display unit 60. The memory unit 50 is a functional unit that functions as a database for storing information. The memory unit 50 is realized, for example, by a database including at least one of a memory and a storage, a server, or other appropriate medium. The display unit 60 is a functional unit that displays input information. The display unit 60 is, for example, a display.

[0032] 2, the measuring device 100 includes a measuring unit 20 (an example of an ionization chamber), a detecting unit 30 (an example of a detector), and a control unit 40. The measuring device 100 performs measurement processing on neutron rays N and gamma rays G in the measuring unit 20, and performs detection processing on neutron rays N in the detecting unit 30. The measurement processing in the measuring unit 20 and the detection processing in the detecting unit 30 are performed at different times using the same water phantom 26, for example.

[0033] The measurement unit 20 is an instrument that measures measurement values ​​related to radiation including neutron rays N and gamma rays G. The measurement unit 20 measures measurement values ​​related to neutron rays N and gamma rays G. The measurement unit 20 is provided, for example, downstream of the charged particle beam P from the target 10 in the neutron capture therapy device 1. Therefore, the measurement values ​​in this embodiment are composed of measurement values ​​related to neutron rays N and measurement values ​​related to gamma rays G. The measurement unit 20 is composed, for example, of an ionization chamber. The measurement unit 20 in this embodiment is an ionization chamber that contains air inside, and is a so-called air ionization chamber. The measurement unit 20 performs measurement based on a measurement control signal from the control unit 40.

[0034] Specifically, measurement unit 20 includes a box 21 filled with air, a pair of electrodes 22, 23 provided facing each other inside box 21, a current measurement unit 24 that measures the current generated between the pair of electrodes 22, 23, and a first measurement device 25 that calculates a measurement value from the measurement result by current measurement unit 24. Measurement of the measurement value by measurement unit 20 is performed using a water phantom 26. That is, neutron beam N and gamma rays G from neutron capture therapy device 1 are irradiated toward water phantom 26. For example, box 21 and the pair of electrodes 22, 23 are provided inside water phantom 26. Box 21 and the pair of electrodes 22, 23 are arranged at predetermined positions within water phantom 26.

[0035] The interior of the box 21 is exposed to the atmosphere, for example, through a conduit extending to the outside of the water phantom 26. The air inside the box 21 contains, for example, nitrogen and oxygen. The interior of the box 21 may be filled with only a gas consisting of nitrogen. The pair of electrodes 22, 23 are made of, for example, a thin metal plate such as copper. The opposing surfaces of the pair of electrodes 22, 23 are covered with films 22a, 23a. A power source is connected between the pair of electrodes 22, 23, and a high-voltage electric field is applied. The current measuring unit 24 is electrically connected to the pair of electrodes 22, 23. The current measuring unit 24 measures the current value applied between the pair of electrodes 22, 23.

[0036] With this configuration, when neutron beams N and gamma rays G pass through the measuring unit 20, they collide with molecules that make up the air, ionizing the molecules. Because an electric field is applied between the pair of electrodes 22, 23, ionized electrons e- are concentrated at one electrode 23, and ions i+ are concentrated at the high-voltage electrode 22. Therefore, the current value changes depending on the number of electrons e- and ions i+ generated by the ionization of the molecules that make up the air. The current measuring unit 24 outputs the measured current value to the first measuring device 25.

[0037] The first measuring device 25 converts the current value measured by the current measuring unit 24 into a predetermined measurement value and transmits it to the control unit 40. The number of electrons e- and ions i+ generated due to the ionization of molecules constituting the air is proportional to the dose of neutron radiation N and the dose of gamma radiation G passing through the box 21. Therefore, the first measuring device 25 calculates a measurement value related to neutron radiation N and a measurement value related to gamma radiation G based on the current value measured by the current measuring unit 24. The first measuring device 25 calculates the amount of ionization as a measurement value using a known method and outputs it to the control unit 40. The first measuring device 25 calculates the amount of ionization, for example, by passing the generated current through a predetermined resistor and converting it into a voltage value.

[0038] The measured value includes a first ionization amount, which is the amount of ionization caused by the reaction between air and neutron beam N, and a second ionization amount, which is the amount of ionization caused by the reaction between air and gamma ray G. At the stage when the first measuring device 25 calculates the measured value, the first ionization amount and the second ionization amount are not distinguished from each other. The first ionization amount and the second ionization amount are each calculated by the control device 40 using the measured value and a detection value described below. Note that the control device 40 may directly receive the detection result from the current measuring device 24 and internally perform the processing performed by the first measuring device 25.

[0039] The detection unit 30 is a device that detects the neutron beam N. The detection unit 30 calculates a detection value related to the neutron beam. The detection unit 30 is provided, for example, downstream of the target 10 in the charged particle beam P in the neutron capture therapy device 1. The detection unit 30 includes a scintillator 31, an optical fiber 32 having the scintillator 31 provided at its tip, a photodetector 33 that detects light transmitted from the optical fiber 32, and a second measuring device 34 that detects a detection value from the detection result by the photodetector 33. The detection unit 30 performs detection based on a measurement control signal from the control unit 40.

[0040] The scintillator 31 is a phosphor that converts incident neutrons into light. The scintillator 31 is electrically connected to an optical fiber 32. The scintillator 31 is, for example, 6The scintillator 31 is made of Li. The internal crystals of the scintillator 31 become excited in response to the dose of incident neutron rays, generating scintillation light. Neutron rays are measured using a water phantom 26. That is, when a neutron ray N is irradiated from the neutron capture therapy device 1 to the detection unit 30, the neutron ray N is irradiated toward, for example, a water phantom 26 that is the same as the water phantom used in the measurement unit 20. For example, after the measurement process of the neutron ray N and the gamma ray G in the measurement unit 20 is completed, the box 21 and the pair of electrodes 22, 23 are removed from the water phantom 26, and the scintillator 31 and a portion of the optical fiber 32 are placed at predetermined positions within the water phantom 26. The position of the scintillator 31 in the water phantom 26 may be changed as appropriate depending on the progress of the measurement.

[0041] The photodetector 33 detects light emitted by the scintillator 31 via the optical fiber 32. The photodetector 33 outputs the detection result to the second measuring device 34. The second measuring device 34 converts the detection result from the photodetector 33 into a predetermined detection value. The second measuring device 34 transmits the detection value to the control device 40. The detection value is, for example, a neutron count for the neutron beam N. The second measuring device 34 counts the number of neutrons as the detection value and outputs it to the control device 40. The control device 40 may directly receive the detection result from the photodetector 33 and internally perform the processing performed by the second measuring device 34. The detection device 30 is configured with, for example, a 1 / v detector. The 1 / v detector is a detector in which the scintillator 31 portion is made of a 1 / v absorber. The 1 / v detector will be described in detail later.

[0042] The control unit 40 controls the entire measurement device 100. The control unit 40 includes a processor, memory, storage, a communication interface, and a user interface, and is configured as a general computer. The processor is a computing unit such as a CPU (Central Processing Unit). The memory is a storage medium such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The storage is a storage medium such as a HDD (Hard Disk Drive). The communication interface is a communication device that realizes data communication. The user interface is an input device such as a keyboard, touch panel, or microphone. The processor controls the memory, storage, communication interface, and user interface, and realizes the functions of the control unit 40, which will be described later. The control unit 40 realizes various functions, for example, by loading a program stored in the ROM into the RAM and executing the program loaded into the RAM with the CPU. The control unit 40 may be composed of multiple computers.

[0043] The control unit 40 includes an acquisition unit 41 , a calculation unit 42 , and an output unit 43 .

[0044] The acquisition unit 41 acquires measured values ​​and detected values. The acquisition unit 41 of this embodiment acquires measured values ​​from the measurement unit 20 and acquires detected values ​​from the detection unit 30. The acquisition unit 41 outputs the measured values ​​and detected values ​​to the calculation unit 42. Note that the acquisition unit 41 may acquire at least one of the measured values ​​and detected values ​​that have been stored in advance in the storage unit 50 from the storage unit 50.

[0045] The calculation unit 42 calculates the dose of gamma rays G based on the measurement values ​​and detection values ​​acquired by the acquisition unit 41. The calculation unit 42 calculates the dose of neutron rays N based on the measurement values ​​measured by the measurement unit 20 and the detection values ​​detected by the detection unit 30. The calculation unit 42 first calculates the first ionization amount. Next, the calculation unit 42 calculates the second ionization amount by subtracting the contribution of the first ionization amount from the overall measurement values. Next, the calculation unit 42 calculates the dose of gamma rays G based on the second ionization amount. The method of calculating each value will be described later.

[0046] The output unit 43 outputs the dose of gamma rays G calculated in the calculation unit 42 to the storage unit 50 or the display unit 60. The output unit 43 outputs the dose of neutron rays N calculated in the calculation unit 42 to the storage unit 50 or the display unit 60. The output unit 43, for example, stores the dose of gamma rays G and the dose of neutron rays N in the storage unit 50. The output unit 43, for example, displays the dose of gamma rays G and the dose of neutron rays N on the display unit 60. The output unit 43 may output the first ionization amount and the second ionization amount to the storage unit 50 or the display unit 60.

[0047] The output unit 43 outputs the dose of gamma rays G to the irradiation control unit 18 of the neutron capture therapy device 1. The output unit 43 may output the dose of neutron rays N to the irradiation control unit 18 of the neutron capture therapy device 1.

[0048] The calculation method of each value in the calculation unit 42 will be described in detail below. air is the amount of ionization of the air in the box 21 by the neutron ray N and the gamma ray G. Therefore, the measured value C air is the first ionization amount C for neutron radiation N neu and the second ionization amount C for gamma rays G γ Using this, the first ionization amount C is calculated as shown in the following formula (1): neu and the second ionization amount C γ It is expressed as the sum of C air =C neu + C γ …(1)

[0049] The composition of the air filled in the box 21 is composed of nitrogen molecules, which account for about 80% of the air, and oxygen molecules, which account for about 20% of the air. The abundance of other components in the air is much smaller than the abundance of nitrogen molecules. Therefore, the amount of ionization caused by the reaction of the neutron beam N with the components in the air other than nitrogen molecules and oxygen molecules is measured C air The effect on the neutron cross section of the nitrogen atom, σ, is so small that it need not be taken into consideration. n(N,p)is 1.930 b (barn), and the neutron cross section of the oxygen atom σ n(O,p) is 189.9 μb (microbarns). Therefore, the neutron cross section of the nitrogen atom, σ n(N,p) is the neutron cross section of the oxygen atom, σ n(O,p) is much larger than the amount of nitrogen ionization C. Therefore, in the ionization of air by neutrons N, the ionization caused by the nuclear reaction between neutrons N and nitrogen molecules is dominant. In other words, in the ionization of air by neutrons N, the contribution of the ionization caused by the nuclear reaction between neutrons N and oxygen molecules is so small that it can be ignored. Therefore, the amount of ionization caused by the reaction between neutrons N and nitrogen molecules is called the amount of nitrogen ionization C n(N,p) The amount of ionization due to the reaction between neutrons N and oxygen molecules is the amount of oxygen ionization C n(O,p) In this case, the first ionization amount C neu is expressed as the following formula (2), and the nitrogen ionization amount C n(N,p) is approximated to

number

[0050] Nitrogen ionization amount C n(N,p) is expressed as the neutron flux Φ as shown in the following equation (3): neu In other words, the amount of nitrogen ionization C n(N,p) is the amount of ionization obtained by the reaction of neutrons N with nitrogen molecules, so the neutron cross section of nitrogen atoms σ n(N,p) is proportional to the number of neutrons passing through a given area per second.

number

[0051] Here, the neutron count R, which is a detection value for neutrons detected by the detection unit 30, can be measured by the detection unit 30 using a nuclear reaction between neutrons and atomic nuclei having a cross section according to the 1 / v law. The neutron count R is the number of reactions of the detection unit 30 (the number of times the detection unit 30 detects neutrons (=reacts with neutrons) within the measurement time). Here, the cross section of the atomic nuclei used in the scintillator 31 of the detection unit 30 is expressed as σ AThen, the neutron count R is calculated by the cross section σ as shown in the following equation (4): A It is proportional to the number of neutrons passing through a given area per second.

number

[0052] Here, the nucleus of a nitrogen atom also has a cross section that follows the 1 / v law, so the same relationship as in equation (4) above holds. Therefore, the nitrogen ionization amount C n(N,p) is expressed as the following equation (5). As shown in equation (5), the nitrogen ionization amount C n(N,p) is proportional to the neutron count R. As shown in equation (2), the first ionization amount C neu is the amount of nitrogen ionization C n(N,p) Therefore, the first ionization amount C neu can be considered to be proportional to the neutron count R.

number

[0053] Therefore, if the detection value (neutron count R) detected by the detection unit 30 and the cross section ratio of the nitrogen and atomic nuclei used in the neutron detector are known, the calculation unit 42 can calculate the first ionization amount C neu Therefore, the calculation unit 42 can calculate the measured value C of the measurement unit 20. air The second ionization amount C is obtained by subtracting γ When the proportionality constant is α, the calculation unit 42 calculates the second ionization amount C γ can be expressed as the following equation (6). The calculation unit 42 calculates the second ionization amount C γ The calculation unit 42 calculates the dose of the gamma rays G using, for example, the second ionization amount C γ The calculation unit 42 calculates the dose of gamma rays G by a known method using the first ionization amount C neu Alternatively, the neutron count R is used to calculate the dose of the neutron radiation N using a known method.

number

[0054] Here, the constraints on using the neutron count R will be explained. First, in order to calculate the neutron count R with high accuracy, the detection unit 30 is configured to include, for example, a 1 / v detector as described above. When a 1 / v detector is used, the above formula (4) holds. Here, a 1 / v absorber is a material that absorbs neutrons whose incident energy is 10 -4 This refers to a material in which the cross section decreases in proportion to 1 / v in the low MeV region or less. A cross section that follows the 1 / v law refers to a cross section that decreases in proportion to 1 / v. Note that the cross section here includes the neutron cross section mentioned above and refers to the microscopic cross section. In other words, the cross section is a measure of the rate at which a nuclear reaction occurs. If the reaction rate (number of reactions per unit time) when a material is exposed to a monoenergetic neutron field is R0 and the number density of the material's nuclei is N0, the cross section is defined by equation (7). The larger the cross section, the easier it is for the absorber to react with neutrons. "v" indicates the speed of neutrons. If the mass per neutron is m, v has the relationship with neutron energy E shown in equation (8). A 1 / v detector is a detector that uses atomic nuclei whose cross section is proportional to 1 / v. There is a proportional relationship between σ and 1 / v, and v and E 1 / 2 Since the proportional relationship between σ and 1 / E holds, 1 / 2 Therefore, when the horizontal axis is plotted as a logarithm of the energy, the cross section and the energy are in a linear relationship, with a slope of -1 / 2, as shown in Figure 3.

number

[0055] As such a 1 / v absorber, 10 B, 6 Li, 14 N, 3 He, etc. Specifically, 10 The graph of FIG. 3 showing the characteristics of B, and 6 As shown in the graph of Li in Fig. 4, the cross section of these absorbers is 10 -4In the low incident energy region below MeV, it decreases in proportion to 1 / v. However, in the high energy region, deviations from the proportional relationship of 1 / v occur, so corrections are required when calculating the cross section in such regions. 197 As shown in the graph of Au in Figure 5, the cross section of the absorber is 10 -4 Even in the low incident energy region below MeV, the proportional relationship of 1 / v deviates. 197 Absorbers such as Au do not qualify as 1 / v absorbers.

[0056] It should be noted that the atoms of the 1 / v absorber used in the detection unit 30 do not necessarily have to match the atoms that are the targets of the reaction number calculation. 10 Even if a 1 / v absorber other than B is used, the calculation unit 42 10 The number of reactions in B can be calculated.

[0057] As mentioned above, the 1 / v absorber requires correction in the high-energy region. To minimize the amount of correction, it is preferable to perform the measurement in a water phantom 26 (see FIG. 2). When performing measurements in air, the neutron field must be sufficiently thermalized. Therefore, the measurement device 100 according to this embodiment is not suitable for detecting epithermal neutron fields. However, since the measurement device 100 detects the neutron count R in the water phantom 26, this constraint does not pose a particular problem.

[0058] The detection head (the scintillator 31 portion) of the detection unit 30 is small. Therefore, if the perturbation effect of the neutron field in water (perturbation effect = distortion effect × self-shielding effect) is not sufficiently small, the uncertainty due to correction will increase. The perturbation effect is the influence caused by the presence of anything other than water at the measurement location. Specifically, it is preferable to keep the distortion effect and self-shielding effect within a sufficiently small range of 1% or less.

[0059] The following describes the irradiation control of the charged particle beam P in the irradiation control unit 18 of the neutron capture therapy device 1. The irradiation control unit 18 controls the irradiation of radiation using the dose of gamma rays G calculated by the measurement device 100. Note that the irradiation control unit 18 may also control the irradiation of radiation using the dose of neutron beam N calculated by the measurement device 100.

[0060] The irradiation control unit 18 of the neutron capture therapy device 1 determines, for example, whether the dose of gamma rays G calculated by the measurement device 100 falls within a predetermined threshold range. If the dose falls within the predetermined threshold range, the neutron capture therapy device 1 ends the measurement by the measurement device 100 and starts irradiation of the patient 16.

[0061] For example, if the dose is not within a predetermined threshold range, the neutron capture therapy device 1 continues measurement by the measurement device 100. In this case, the irradiation control unit 18 controls (adjusts) the dose of the charged particle beam P irradiated from the accelerator 2 based on the dose of the gamma rays G calculated by the measurement device 100. When the accelerator 2 irradiates the charged particle beam P controlled by the irradiation control unit 18, the measurement device 100 calculates an updated dose of the gamma rays G by measuring the radiation including the neutron beam N and the gamma rays G again.

[0062] The neutron capture therapy device 1 can receive feedback of each dose from the measuring device 100 until the dose of the gamma rays G falls within a predetermined threshold range. Note that the neutron capture therapy device 1 may also receive feedback of each dose from the measuring device 100 until the dose of the neutron rays N falls within a predetermined threshold range.

[0063] Next, the procedure of the measurement method according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the processing of the neutron beam measurement method. The flowchart shown in Fig. 6 is started, for example, when the neutron capture therapy device 1 irradiates a charged particle beam P and the measurement unit 20 receives a measurement control signal from the control unit 40. First, the measurement unit 20 calculates a measurement value C as a measurement process. airWhen radiation including neutron rays N and gamma rays G is irradiated from the neutron capture therapy device 1 toward the box body 21 in the water phantom 26, the current measuring unit 24 measures the current value generated between the pair of electrodes 22, 23. The first measuring device 25 calculates a measured value C based on the current value obtained by the current measuring unit 24. air (ionization amount) and the measured value C air is output to the control unit 40.

[0064] Next, as a detection process, the detection unit 30 detects the neutron count R, which is a detection value (step S212). When a neutron beam N is irradiated from the neutron capture therapy device 1 toward the scintillator 31 in the water phantom 26, the photodetector 33 detects light emitted by the scintillator 31. Even when gamma rays G are irradiated from the neutron capture therapy device 1 to the scintillator 31, the value of the neutron count R in the scintillator 31 is not significantly affected, so the effect of the gamma rays G can be ignored. The second measuring device 34 calculates the neutron count R based on the detection result obtained by the photodetector 33 and outputs the neutron count R to the control unit 40.

[0065] Next, the acquisition unit 41 of the control unit 40 acquires the measurement value C air and the detected value (neutron count R) (step S214). air The acquisition unit 41 acquires the neutron count R from the detection unit 30. The acquisition unit 41 acquires the measurement value C air The detected value (neutron count R) is output to the calculation unit 42.

[0066] Next, the calculation unit 42 of the control unit 40 calculates the dose of gamma rays as a calculation process (step S216). The calculation unit 42 calculates the first ionization amount C neu The calculation unit 42 calculates the measured value C air and the first ionization amount C neu Based on this, the second ionization amount C γ The calculation unit 42 calculates the second ionization amount C γThe calculation unit 42 calculates the dose of gamma rays G based on the first ionization amount C neu The calculation unit 42 calculates the dose of the gamma rays G and the dose of the neutron rays N based on the above.

[0067] Subsequently, as an output process, the output unit 43 of the control unit 40 outputs the doses of gamma rays G and neutron rays N to the storage unit 50 or the display unit 60 (step 218). The output unit 43, for example, causes the storage unit 50 to store the doses of gamma rays G and neutron rays N. The output unit 43, for example, causes the display unit 60 to display the doses of gamma rays G and neutron rays N.

[0068] Next, the actions and effects of the measuring apparatus 100 according to this embodiment will be described in comparison with a measuring apparatus 300 according to a comparative example. When the names and symbols of devices or functional units in the measuring apparatus 300 of the comparative example are the same as the names and symbols of devices or functional units in the measuring apparatus 100 of the above-described embodiment, the devices or functional units in the measuring apparatus 300 are considered to have the same functions as the devices or functional units in the measuring apparatus 100.

[0069] FIG. 7 is a block diagram of a measurement system and a measurement device according to a comparative example. As shown in FIG. 7, the measurement system 400 includes a neutron capture therapy device 1 and a measurement device 300. The measurement device 300 includes a first gas measurement unit 310, a second gas measurement unit 320, a detection unit 30, and a control unit 40. The measurement device 300 of the comparative example calculates the dose of neutron radiation N and the dose of gamma radiation G. The first gas measurement unit 310 includes a box 311 filled with a first gas, a pair of electrodes 22 and 23, a current measurement unit 24, a first measurement device 25, and a first gas supply unit 317 that supplies the first gas to the box 311. The box 311 is provided inside a water phantom 26. The first gas filled inside the box 311 is, for example, carbon dioxide gas. The first gas is supplied from the first gas supply unit 317 through a gas pipe. The first gas supply unit 317 is, for example, a gas tank. The pair of electrodes 22 and 23 are provided inside the box body 311.

[0070] The second gas measurement unit 320 includes a box 321 filled with a second gas, a pair of electrodes 22, 23, a current measurement unit 24, a first measurement device 25, and a second gas supply unit 327 that supplies the second gas into the box 321. The box 321 is provided inside the water phantom 26. The type of the second gas filled inside the box 321 is different from the first gas. The second gas is, for example, a mixed gas of methane gas, carbon dioxide gas, and nitrogen gas. The second gas is supplied from the second gas supply unit 327 through a gas pipe. The second gas supply unit 327 is, for example, a gas tank. The pair of electrodes 22, 23 are provided inside the box 321.

[0071] The neutron beam N from the neutron capture therapy device 1 to the second gas measurement unit 320 is irradiated toward, for example, a water phantom 26 that is the same as the water phantom used in the first gas measurement unit 310. For example, after the measurement of the neutron beam N and gamma rays G in the first gas measurement unit 310 is completed, the box 311 and the pair of electrodes 22, 23 provided inside the box 311 are removed from the water phantom 26. Next, the box 321 and the pair of electrodes 22, 23 provided inside the box 321 are placed at predetermined positions within the water phantom 26. The neutron beam N from the neutron capture therapy device 1 to the detection unit 30 of the measurement device 300 is also irradiated toward, for example, the water phantom 26 that is the same as the water phantom used in the first gas measurement unit 310. For example, after the measurement of neutron rays N and gamma rays G in the second gas measurement unit 320 is completed, the box 321 and the pair of electrodes 22, 23 provided inside the box 321 are removed from the water phantom 26. Next, the scintillator 31 and a part of the optical fiber 32 are placed at predetermined positions within the water phantom 26.

[0072] The first gas measuring unit 310 and the second gas measuring unit 320 provided in the measuring device 300 have different sensitivities because the types of gases that flow into them are different. The measuring device 300 calculates the dose of gamma rays G using the measurement values ​​obtained by the first gas measuring unit 310 and the second gas measuring unit 320. That is, to calculate the dose of gamma rays G in the measuring device 300, a total of two measurement processes are required: a measurement process in the first gas measuring unit 310 and a measurement process in the second gas measuring unit 320. The measuring device 300 also calculates the dose of neutron rays N using the detection value in the detection unit 30. That is, to calculate the dose of neutron rays N in the measuring device 300, one detection process in the detection unit 30 is required. Therefore, in order to calculate the dose of gamma rays G and neutron rays N in the neutron capture therapy device 1 using the comparative example measurement device 300, a total of three processes are required, consisting of a measurement process in the first gas measurement unit 310, a measurement process in the second gas measurement unit 320, and a detection process in the detection unit 30.

[0073] In the measuring device 100 of this embodiment, the dose of gamma rays G can be calculated and the dose of neutron rays N can be calculated by a total of two processes, which are the measurement process in the measuring unit 20 and the detection process in the detecting unit 30. Therefore, compared to the measuring device 300 of the comparative example, the measuring device 100 of this embodiment can reduce the number of processes up to the calculation of the dose of gamma rays G and the dose of neutron rays N, and can easily calculate the doses.

[0074] Furthermore, the first gas measuring unit 310 and the second gas measuring unit 320 of the measuring device 300 of the comparative example need to have different sensitivities in order to calculate the dose of gamma rays G. Therefore, in the measuring device 300, the first gas supplied to the first gas measuring unit 310 and the second gas supplied to the second gas measuring unit 320 need to be different types of gases. Therefore, in order to obtain the dose of gamma rays G in the measuring device 300, a first gas supply unit 317 and a second gas supply unit 327 need to be provided.

[0075] On the other hand, in the measurement unit 20 of the measurement device 100 of this embodiment, since the inside of the box 21 is exposed to the atmosphere, it is not necessary to provide equipment for filling the box 21 with gas. Even if such equipment is provided, it is sufficient to provide only equipment for filling one type of gas (air) into the box 21. Therefore, compared to the measurement device 300 of the comparative example, the measurement device 100 of this embodiment can reduce the cost and labor required for providing equipment for filling gas, and can easily perform processing up to calculation of the dose of gamma rays G and the dose of neutron rays N.

[0076] As described above, the measurement device 100 is configured to measure the radiation including neutron rays N and gamma rays G measured in the measurement unit 20 having the box 21 (ionization chamber) containing air. air and the neutron count R (detection value) of the neutron ray N detected by the detection unit 30 (detector), the dose of the gamma ray G is calculated.

[0077] The measurement device 100 of this embodiment measures radiation including neutron rays N and gamma rays G in the measurement unit 20. air and the neutron count R detected by the detection unit 30, the dose of gamma rays G is calculated. air Since the measurement is performed in the box 21 containing air, the measurement can be easily performed without providing a separate facility for filling the box 21 with gas. air Using the neutron count R, the first ionization amount C, which is the value related to the neutron radiation N, is calculated. neu The influence of the gamma rays G can be eliminated. As described above, the measurement device 100 can easily measure the dose of the gamma rays G. The measurement device 100 can also easily measure the dose of the neutron rays N. That is, the dose of the gamma rays G and the dose of the neutron rays N can be appropriately and easily calculated in order to ensure the quality of the beam irradiated in the neutron capture therapy device 1.

[0078] Measurement value C air is the first ionization amount C due to the reaction between the air in the box 21 and the neutron beam N. neuand the second ionization amount C due to the reaction between the air in the box 21 and the gamma ray G. γ and the second ionization amount C γ The dose of gamma rays G is calculated based on the measured value C air , first ionization amount C neu and the second ionization amount C based on the neutron count R. γ can be derived and the dose of gamma rays G can be measured appropriately.

[0079] The detected value is the neutron count R for the neutron beam N, and the first ionization amount C neu is the nitrogen ionization amount C, which is the amount of ionization caused by the reaction between nitrogen contained in the air in the box 21 and the neutron beam N. n(N,p) In this case, the first ionization amount C neu can be considered to be proportional to the neutron count R, so the first ionization amount C neu is calculated based on the neutron count R. This gives the measured value C air From the first ionization amount C neu By removing the second ionization amount C γ can be derived, and the dose of gamma rays G can be measured appropriately.

[0080] The measurement device 100 of this embodiment calculates the neutron flux Φ as shown in equation (6). neu Second ionization amount C without using γ It is possible to calculate the neutron flux Φ neu Using the second ionization amount C γ When calculating the neutron cross section and neutron flux Φ neu Since the energy integral with γ Therefore, the calculation unit 42 calculates the neutron flux Φ neu The second ionization amount C is calculated using a formula that does not include γ By calculating the second ionization amount C γ The accuracy can be improved.

[0081] A measurement method according to another aspect of the present disclosure is a method for measuring radiation including neutron rays N and gamma rays G measured in a measurement unit 20 having a box 21 (ionization chamber) containing air therein. air and a step (step S216) of calculating the dose of the gamma rays G based on the neutron count R (detection value) of the neutron rays N detected by the detection unit 30 (detector).

[0082] According to this measurement method, the same actions and effects as those of the measurement device 100 described above can be obtained.

[0083] A measurement system 200 according to another aspect of the present disclosure includes a neutron capture therapy device 1 (radiation therapy device) that irradiates radiation (charged particle beam P) including neutron beams N and gamma rays G, and a measurement value C related to radiation measured in a box 21 (ionization chamber) containing air. air and a measuring device 100 that calculates the dose of gamma rays G irradiated from the neutron capture therapy device 1 based on a neutron count R (detection value) regarding the neutron rays N detected by a detection unit 30 (detector).

[0084] According to this measurement system 200, the measurement device 100 measures the radiation (charged particle beam P) emitted from the neutron capture therapy device 1. air and the neutron count R of the neutron ray N irradiated from the neutron capture therapy device 1, the dose of the gamma ray G is calculated. air is measured in the box 21 containing air, it can be easily measured without providing a separate facility for filling the box 21 with gas. air The influence of the value related to the neutron ray N can be eliminated by using the neutron count R from the neutron capture therapy device 1. As described above, the measurement system 200 can easily measure the dose of gamma rays G from the neutron capture therapy device 1 using the measurement device 100. Furthermore, the measurement system 200 can also easily measure the dose of neutron ray N from the neutron capture therapy device 1 using the measurement device 100.

[0085] A measurement system 200 (an example of a radiation therapy system) according to another aspect of the present disclosure includes a neutron capture therapy device 1 (radiation therapy device) that irradiates radiation (charged particle beam P) including neutron beam N and gamma ray G, and a measurement value C related to radiation measured in a box 21 (ionization chamber) containing air inside. air and a measuring device 100 that calculates the dose of gamma rays G irradiated from the neutron capture therapy device 1 based on the neutron count R (detection value) for the neutron rays N detected by the detection unit 30 (detector), and the radiation therapy device controls the irradiation of radiation using the dose of gamma rays calculated by the measuring device.

[0086] According to this measurement system 200, the neutron capture therapy device 1 can irradiate the patient 16 with an appropriate dose of radiation by controlling the irradiation of radiation including neutron rays N and gamma rays G using at least one of the dose of neutron rays N and the dose of gamma rays G that are accurately calculated by the measurement device 100. Furthermore, the neutron capture therapy device 1 can suppress irradiation of the patient 16 with radiation including at least one of neutron rays N and gamma rays G having a dose exceeding a predetermined threshold.

[0087] The present disclosure is not limited to the above-described embodiments.

[0088] In the above embodiment, the calculation unit 42 calculates the dose of the neutron beam N, but the dose of the neutron beam N does not have to be calculated. The measurement device 100 does not have to include at least one of the measurement unit 20 and the detection unit 30. When the measurement device 100 does not include the measurement unit 20, the acquisition unit 41 acquires the measurement value C stored in advance in the storage unit 50. air may be acquired from the storage unit 50. When the measurement device 100 does not include the detection unit 30, the acquisition unit 41 may acquire from the storage unit 50 the neutron count R (detection value) that has been stored in advance in the storage unit 50.

[0089] The measuring device 100 can use a detector other than a scintillator as the detection unit 30. For example, as a detector for counting the number of neutrons, 3 He gas proportional counter,10 A proportional counter coated with B may be used. The detection method is not particularly limited, but a method that counts neutrons is preferred.

[0090] In the measuring device 100, the box 21 and the scintillator 31 may be provided in the same water phantom. Within the water phantom, the positions of the box 21 and the scintillator 31 may be determined arbitrarily. Therefore, by irradiating the water phantom with neutron beams N and gamma rays G from the neutron capture therapy device 1, both measured values ​​and detected values ​​can be obtained. In this case, the measuring process (S210) and the detecting process (S212) may be executed in parallel.

[0091] Furthermore, the detection process (S212) may be performed before the measurement process (S210). In this case, for example, when the detection of the neutron beam N in the detection unit 30 is completed, the scintillator 31 and a part of the optical fiber 32 may be removed from the water phantom 26, and the box 21 and the pair of electrodes 22, 23 may be placed at predetermined positions within the water phantom 26.

[0092] In the measurement system 200, the measurement device 100 may output the dose of gamma rays G and the dose of neutron rays N to a calibration device (not shown). The calibration device is a device that acquires an estimated value related to the fluence of neutron rays N in the neutron capture therapy device 1, compares it with the measurement result of the measurement device 100, and calibrates the estimated value. In the measurement system 200, the calibration device may be connected to a treatment planning device (not shown) included in the measurement system 200. In this case, the calibration device transmits the estimated value to the treatment planning device. The treatment planning device is a device that creates a treatment plan for how to irradiate neutron rays N to a patient when performing treatment using the neutron capture therapy device 1. That is, the measurement system 200 can calibrate the estimated value related to the fluence of neutron rays N in the neutron capture therapy device 1 based on the result (the dose of neutron rays N or the dose of gamma rays G) obtained by the measurement device 100, and set an appropriate treatment plan for the neutron capture therapy device 1. [Explanation of symbols]

[0093] 1...neutron capture therapy device, 10...target, 18...irradiation control unit, 20...measurement unit, 21...box body, 30...detection unit, 31...scintillator, 40...control unit, 41...acquisition unit, 42...calculation unit, 43...output unit, 50...storage unit, 60...display unit, 100...measuring device, 200...measurement system (an example of a measurement system and a radiation therapy system), C air …measurement value, C neu …first ionization, C γ ...second ionization amount, G...gamma rays, N...neutron rays, P...charged particle rays, R...neutron count.

Claims

1. Measurement values ​​measured in an ionization chamber containing air include a first ionization amount due to a reaction between the air in the ionization chamber and neutron rays and a second ionization amount due to a reaction between the air in the ionization chamber and gamma rays; a detection value, which is a neutron count for the neutron beam detected by the detector; calculating the amount of nitrogen ionization due to the reaction between nitrogen contained in the air in the ionization chamber and the neutron beam based on the neutron count; The first ionization amount is approximated to the nitrogen ionization amount; The measuring device calculates the dose of the gamma rays based on the second ionization amount obtained by subtracting the nitrogen ionization amount from the measurement value.

2. A measuring device as described in claim 1, wherein the nitrogen ionization amount is calculated based on a relationship in which the nitrogen ionization amount is proportional to the neutron count.

3. Measurement values ​​measured in an ionization chamber containing air include a first ionization amount due to a reaction between the air in the ionization chamber and neutron rays and a second ionization amount due to a reaction between the air in the ionization chamber and gamma rays; acquiring a detection value, which is a neutron count for the neutron beam detected in a detector; calculating the amount of nitrogen ionization due to a reaction between nitrogen contained in the air in the ionization chamber and the neutron beam based on the neutron count; The first ionization amount is approximated to a nitrogen ionization amount; and calculating the dose of the gamma rays based on the second ionization amount obtained by subtracting the nitrogen ionization amount from the measurement value.

4. a radiation therapy device that irradiates radiation including neutron rays and gamma rays; Measurement values ​​measured in an ionization chamber containing air include a first ionization amount due to a reaction between the air in the ionization chamber and the neutron beam, and a second ionization amount due to a reaction between the air in the ionization chamber and the gamma ray; a detection value, which is a neutron count for the neutron beam detected by the detector; calculating the amount of nitrogen ionization due to the reaction between nitrogen contained in the air in the ionization chamber and the neutron beam based on the neutron count; The first ionization amount is approximated to a nitrogen ionization amount; a measuring device that calculates the dose of the gamma rays based on the second ionization amount obtained by subtracting the nitrogen ionization amount from the measurement value.

5. a radiation therapy device that irradiates radiation including neutron rays and gamma rays; Measurement values ​​measured in an ionization chamber containing air include a first ionization amount due to a reaction between the air in the ionization chamber and the neutron beam, and a second ionization amount due to a reaction between the air in the ionization chamber and the gamma ray; a detection value, which is a neutron count for the neutron beam detected by the detector; calculating the amount of nitrogen ionization due to the reaction between nitrogen contained in the air in the ionization chamber and the neutron beam based on the neutron count; The first ionization amount is approximated to the nitrogen ionization amount; a measuring device that calculates the dose of the gamma rays based on the second ionization amount obtained by subtracting the nitrogen ionization amount from the measurement value, The radiation therapy device controls the irradiation of the radiation using the dose of the gamma rays calculated by the measuring device.

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