TW202142283A - Neutron beam measuring device and neutron beam measuring method - Google Patents

Abstract

To provide a neutron beam measuring device which can easily measure a neutron beam, and can improve measurement accuracy, and a neutron beam measuring method. A neutron beam measuring device 100 comprises a detection part 30 for detecting a neutron beam N, and a common-use neutron fluence calculation part 41 for calculating a quantity of the neutron beams N on the basis of a detection result of the detection part 30. Here, the common-use neutron fluence calculation part 41 calculates a common-use neutron fluence. By this constitution, measurement can be easily performed, and measuring accuracy can be improved. The common-use neutron fluence does not exist in an average cross section area in which uncertainty is large like a thermal neutron fluence. Therefore, the uncertainty of the measurement can be reduced. By reducing the uncertainty of the measurement as above, the uncertainty of a normalization constant of a treatment planning device 200 can be also reduced. Also, the common-use neutron fluence can easily perform the measurement since a calculation becomes possible by a one-time measurement without using a filter or the like.

Description

Neutron beam measuring device and neutron beam measuring method

The invention relates to a neutron beam measuring device and a neutron beam measuring method. This application claims priority based on Japanese Patent Application No. 2019-234475 filed on December 25, 2019. The entire content of this Japanese application is incorporated in this specification by reference.

In recent years, there have been technologies that use neutron beams for treatment. For example, as a neutron capture therapy that irradiates a neutron beam to kill cancer cells, a boron neutron capture therapy (BNCT: Boron Neutron Capture Therapy) using a boron compound is known. In the boron neutron capture therapy, neutron beams are irradiated to the boron that has been absorbed by the cancer cells in advance, and the resulting heavy charged particles are scattered to selectively destroy the cancer cells.

In order to measure the amount of the neutron beam used for treatment in this way, for example, a neutron beam measuring device shown in Patent Document 1 is used. In the neutron beam measuring device shown in Patent Document 1, the neutron beam is detected by the detection unit, and the amount of the neutron beam is calculated based on the detection result. [Prior Technical Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2016-166777

[The problem to be solved by the invention]

Among them, in order to improve the measurement accuracy of the neutron beam measuring device as described above, it is sometimes based on the difference between the measurement result of a filter that cuts off the thermal neutron beam on the detector and the measurement result of no filter. Measure the neutron beam. However, in such a neutron beam measuring device, two measurements are required, so there is a problem that the measurement becomes complicated. In addition, the measurement results may contain uncertainty. Therefore, it is required to be able to perform measurement easily and improve measurement accuracy.

Therefore, the object of the present invention is to provide a neutron beam measurement device and a neutron beam measurement method that can easily perform neutron beam measurement and can improve the measurement accuracy. [Technical means to solve the problem]

The neutron beam measuring device of the present invention measures the amount of neutron beam generated by irradiating a charged particle beam to a target. The neutron beam measuring device includes: a detection unit that detects the neutron beam; and a calculation unit, according to the detection unit The amount of neutron beam is calculated based on the detection result of, and the calculation unit calculates at least one of the conventional neutron fluence rate and the conventional neutron fluence rate (conventional neutron fluence rate).

The neutron beam measuring device of the present invention includes: a detection unit that detects a neutron beam; and an arithmetic unit that calculates the amount of neutron beam based on the detection result of the detection unit. Among them, the computing unit computes at least one of the regular neutron fluence and the regular neutron fluence rate. With the above, the measurement can be easily performed and the measurement accuracy can be improved. The conventional neutron fluence and conventional neutron fluence rate are different from the true thermal neutron fluence and do not depend on the average cross-sectional area with large uncertainty. Therefore, the uncertainty of measurement can be reduced. In addition, the conventional neutron fluence and the conventional neutron fluence rate can be calculated by one measurement without using a filter or the like, so the measurement can be easily performed. With the above, the measurement of the neutron beam can be easily performed and the measurement accuracy can be improved.

In the neutron beam measuring device, the detection unit may be configured to include a 1/v detector. At this time, the conventional neutron fluence can depend on the neutron count value. Therefore, the uncertainty of measurement can be reduced.

The neutron beam measuring device is also provided with a display unit for displaying information, and the display unit can display at least one of the normal neutron fluence and the normal neutron fluence rate. Thereby, at least one of the normal neutron fluence and the normal neutron fluence rate can be grasped from the display unit, and therefore, at least one of the calculated normal neutron fluence and the normal neutron fluence rate can be effectively used.

In the neutron beam measuring device, the computing unit can compute the predetermined number of reactions of atoms based on the conventional neutron fluence. Thereby, the number of reactions of specific atoms can be effectively used.

In the neutron beam measuring device, the calculation unit can calculate the kerma dose based on the number of reactions. In this way, the Kema dose can be effectively used.

The neutron beam measuring device can measure at least one of conventional neutron fluence rate, reaction rate and Kema dose rate. At this time, the amount of neutron beam can be grasped in real time according to time.

In the neutron beam measuring device, the computing unit can calculate the conventional neutron fluence rate, response rate, and gamma dose by dividing at least one of the conventional neutron fluence, reaction number, and gamma dose by the irradiation time of the charged particle beam The average of at least one of the rates. At this time, it is possible to grasp the amount of neutron beam over the entire irradiation time.

The neutron beam measurement method of the present invention measures the amount of neutron beam generated by irradiating a charged particle beam to a target. The neutron beam measurement method includes: a detection step, a detection neutron beam; and a calculation step, according to the detection step Calculate the amount of neutron beam from the measurement result of one measurement of, and calculate at least one of the conventional neutron fluence and the conventional neutron fluence rate in the operation step.

According to the neutron beam measurement method of the present invention, the same action/effect as the above-mentioned neutron beam measurement device can be obtained. [Effects of the invention]

According to the present invention, it is possible to provide a neutron beam measurement device and a neutron beam measurement method that can easily perform measurement and can improve measurement accuracy.

Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the drawings.

First, referring to FIG. 1, an overview of a neutron capture therapy device that generates a neutron beam to be a measurement target of the neutron beam measurement device according to the embodiment of the present invention will be described. The neutron capture therapy device 1 shown in FIG. 1 is a device for cancer treatment using boron neutron capture therapy (BNCT: Boron Neutron Capture Therapy). In the neutron capture therapy device 1, for example, a neutron beam N is irradiated to a tumor of a patient (irradiated body) 50 to which ^{boron (10 B) has been administered.}

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 R. The accelerator 2 is composed of, for example, a cyclotron. In this embodiment, the charged particle beam R is a proton beam generated by stripping charges from anions. The accelerator 2 generates, for example, a charged particle beam R with a beam radius of 40 mm and 60 kW (=30 MeV×2 mA). Furthermore, the accelerator is not limited to a cyclotron, and can also be a synchrotron, a synchrocyclotron, a linear accelerator, an electrostatic accelerator, etc.

The charged particle beam R emitted from the accelerator 2 is sent to the neutron beam generator M. The neutron beam generator M is formed by the beam guide 9 and the target 10. The charged particle beam R emitted from the accelerator 2 passes through the beam guide 9 and travels toward the target 10 arranged at the end of the beam guide 9. A plurality of quadrupole electromagnets 4 and scanning electromagnets 6 are provided along the beam guide 9. The plurality of quadrupole electromagnets 4 use electromagnets to adjust the beam axis of the charged particle beam R, for example.

The scanning electromagnet 6 scans the charged particle beam R and performs irradiation control of the charged particle beam R on the target 10. The scanning electromagnet 6 controls the irradiation position of the charged particle beam R on the target 10.

The neutron capture therapy device 1 generates a neutron beam N by irradiating a charged particle beam R on a target 10 and emits the neutron beam N toward the patient 50. The neutron capture therapy device 1 includes a target 10, a shielding body 8, a deceleration member 39, and a collimator 20.

The target 10 is irradiated with the charged particle beam R to generate a neutron beam N. The target 10 is a solid-shaped member formed of a material that generates a neutron beam by being irradiated with a charged particle beam. Specifically, the target 10 is formed of, for example, beryllium (Be), lithium (Li), tantalum (Ta), or tungsten (W), and has, for example, a disk-shaped solid shape with a diameter of 160 mm. Furthermore, the target 10 is not limited to a disc shape, and may have other shapes.

The target 10 is connected to the cooling member 120. The cooling member 120 has, for example, a plurality of grooves on the contact surface that is in contact with the target 10, and the target 10 is cooled by flowing a cooling fluid through the grooves.

The deceleration member 39 decelerates the neutron beam N generated by the target 10 (decreases the energy of the neutron beam N). The deceleration member 39 may have a laminated structure formed by a layer 39A that mainly decelerates the fast neutrons contained in the neutron beam N and a layer 39B that mainly decelerates the superthermal neutrons contained in the neutron beam N.

The shielding body 8 shields the generated neutron beam N and the gamma rays generated with the generation of the neutron beam N to prevent them from being emitted to the outside. The shielding body 8 is provided to surround the deceleration member 39. The upper and lower portions of the shielding body 8 extend from the speed reduction member 39 to the upstream side of the charged particle beam R.

The collimator 20 shapes the radiation field of the neutron beam N, and has an opening 20a through which the neutron beam N passes. The collimator 20 is, for example, a block-shaped member having an opening 20a in the center.

Next, referring to FIG. 2, the detailed structure of the neutron beam measuring apparatus 100 of this embodiment will be described. The neutron beam measuring device 100 is a measuring device that measures the amount of the neutron beam N generated by irradiating the target 10 with the charged particle beam R.

The neutron beam measurement device 100 measures the neutron beam N irradiated from the neutron capture therapy device 1 and outputs the measurement result to the treatment planning device 200 or the display unit 60. The treatment planning device 200 is a device for planning how to irradiate the patient with the neutron beam N when the neutron capture therapy device 1 is used for treatment. In the case of creating a treatment plan by the treatment planning device 200, it is necessary to grasp how much flux the neutron beam N of the neutron capture therapy device 1 has. Therefore, the adjustment (standardization) of the treatment planning device 200 is performed at the stage before treatment by the neutron capture therapy device 1. In the standardization, the normalization constant of the treatment planning device 200 is determined by comparing the flux calculated by the treatment planning device 200 with the measurement result of the neutron beam measuring device 100. For example, the graph of FIG. 3 represents the flux of the neutron beam N at a predetermined depth of the water prosthesis 35 (see FIG. 2). As shown in FIG. 3(a), before standardization, the calculation result of the treatment planning device 200 deviates from the measurement value in the neutron beam measuring device 100. Therefore, as shown in FIG. 3(b), the normalization constant is adjusted so that the calculation result of the treatment planning device 200 corresponds to the measurement value in the neutron beam measurement device 100. Furthermore, in FIG. 3, the measured values in a plurality of parts are used for normalization, but it is also possible to use only the measured values in one part for normalization.

As shown in FIG. 2, the neutron beam measurement device 100 includes a detection unit 30, a control unit 40, and a display unit 60.

The detection unit 30 is a machine that detects the neutron beam. The detection unit 30 includes: a scintillator 31; an optical fiber 32 with the scintillator 31 provided at the tip; a photodetector 33 that detects light transmitted from the optical fiber 32; and a measuring device 34 that measures the detection result based on the photodetector 33. The detection unit 30 performs measurement according to the measurement control signal from the treatment planning device 200.

The scintillator 31 is a phosphor that converts the incident neutron beam into light. The scintillator 31 turns the internal crystal into an excited state according to the dose of the incident neutron beam and generates scintillation light. Regarding the measurement of the neutron beam, a water prosthesis 35 is used. That is, the neutron beam N from the neutron capture therapy device 1 is irradiated toward the water prosthesis 35. Therefore, the scintillator 31 is arranged at a predetermined position in the water phantom 35. The position of the scintillator 31 in the water prosthesis 35 is appropriately changed as the measurement progresses. The light detector 33 detects the light emitted by the scintillator 31 via the optical fiber 32.

The measuring device 34 converts the detection result from the photodetector 33 into a predetermined measurement value, and transmits it to the control unit 40. The measuring device 34 counts the number of neutrons based on the detection result of the photodetector 33 and outputs it to the control unit 40. Furthermore, the control unit 40 can directly receive the detection result from the photodetector 33 and perform the processing performed by the measuring device 34 internally. In this embodiment, the detection unit 30 is configured to include a 1/v detector. The 1/v detector is a detector in which a part of the scintillator 31 is composed of a 1/v absorbent. In addition, the details of the 1/v detector will be described later.

The control unit 40 controls the entire neutron beam measuring device 100. The control unit 40 includes a processor, a memory, a storage, a communication interface, and a user interface, and is configured as a normal computer. The processor is an arithmetic unit such as a CPU (Central Processing Unit: Central Processing Unit). The memory is a storage medium such as ROM (Read Only Memory) or RAM (Random Access Memory). The storage is a storage medium such as HDD (Hard Disk Drive). The communication interface is a communication machine that realizes data communication. The user interface is an input device such as a keyboard, touch panel, or microphone. The processor collectively includes memory, storage, communication interface, and user interface, and implements the functions of the control unit 40 described later. In the control unit 40, for example, the program stored in the ROM is loaded into the RAM, and the CPU executes the program loaded into the RAM, thereby realizing various functions. The control unit 40 may be composed of a plurality of computers.

The control unit 40 includes a normal neutron fluence calculation unit 41 (arithmetic unit), a reaction number calculation unit 42 (arithmetic unit), a Koma dose calculation unit 43 (arithmetic unit), an input unit 44, and a measured value output unit 46.

The conventional neutron fluence calculation unit 41 calculates the amount of neutron beam N based on the detection result detected by the detection unit 30. The normal neutron fluence calculation unit 41 calculates the normal neutron fluence. The conventional neutron fluence calculation unit 41 uses the neutron count obtained from the detection unit 30, the calibration constant input from the input unit 44, and the correction coefficient input from the input unit 44 to calculate the following equation (1). The calibration constant is a value determined as a value peculiar to the neutron beam measuring device 100. Regarding the calibration constant, it is determined by taking the neutron beam measuring device 100 to a calibration field of a national standard in advance for measurement. The method of determining the calibration constant will be described later. The correction coefficient is a coefficient set for the energy characteristics of the detection unit 30, and is a value set in advance according to the type of the detection unit 30 and the like. The conventional neutron fluence calculation unit 41 outputs the calculation result to the reaction number calculation unit 42 and the measured value output unit 46. Conventional neutron fluence=neutron count×calibration constant×correction coefficient……(1)

The reaction number calculation unit 42 calculates the reaction number of a predetermined atom based on the normal neutron fluence. The reaction number calculation unit 42 uses the normal neutron fluence input from the normal neutron fluence calculation unit 41 and the cross-sectional area preset for a predetermined atom to calculate the following formula (2). The cross-sectional area is the cross-sectional area of 2200 m/s of the atom to be calculated. Furthermore, 2200m/s represents the velocity (energy) of neutrons. The reaction number calculation unit 42 outputs the calculation result to the Kema dose calculation unit 43 and the measured value output unit 46. Number of reactions = conventional neutron fluence × cross-sectional area ……(2)

The Kema dose calculation unit 43 calculates the Kema dose based on the number of responses. The Kema dose calculation unit 43 uses the reaction number input from the reaction number calculation unit 42 to calculate the following formula (3). E represents energy. As the energy, the sum of the average kinetic energy of the charged particles emitted when the atom and the neutron react once (usually called the Q value). For example, if it is ⁶ Li, the Q value is 4.89 MeV. If it is ¹⁰ B, the Q value is 2.31 MeV. If it is ¹⁴ N, the Q value is 0.62 MeV. F is the mass density. For example, in the case of calculating the kema dose of boron, it is better to set the mass density to 1 ppm, and in the case of calculating the kema dose other than boron, it is better to use the tissue density defined in ICRU46. M is the value of atomic mass, and it is preferable to set it to a value of 6, in the case of ^{6 Li, 10} in the case of 10 B, and ¹⁴ in the case of 14 N. M _AMU is the value of the atomic mass unit, and it is better to ^{set the value to 1.660539040×10 -27 kg.} The Kema dose calculation unit 43 outputs the calculation result to the measured value output unit 46.

The input unit 44 inputs various information to the control unit 40. The input unit 44 inputs the correction coefficient and the calibration coefficient from the user from the treatment planning device 200 or via an interface such as a mouse or a keyboard. In addition, the input unit 44 inputs information on whether it is necessary to calculate the number of reactions and information on whether it is necessary to calculate the kema dose. The measured value output unit 46 outputs the acquired measured value to the treatment planning device 200 or the user. The measured value output unit 46 directly outputs the measured value as data to the treatment planning device 200. In addition, the measured value output unit 46 visually displays the measured value on the display unit 60. The display unit 60 is composed of a display or the like. The display unit 60 displays the conventional neutron fluence, the number of reactions, and the dose of grams of horses. The display method of the measured value based on the display unit 60 is not particularly limited, and the numerical value may be directly displayed, or it may be converted into a graph or the like for display.

Next, referring to FIG. 4, the procedure of the neutron beam measurement method in this embodiment will be described. First, the scintillator 31 of the detection unit 30 is installed on the neutron field of the measurement target (among them, the water phantom 35) (step S10). Next, the detection unit 30 measures the neutron count (step S20: detection step). Next, the normal neutron fluence calculation unit 41 calculates the normal neutron fluence based on the detection result in one measurement in S10 (step S30: normal neutron fluence calculation step).

Among them, the reaction number calculation unit 42 refers to the input information or setting status in the input unit 44 to determine whether it is necessary to calculate the reaction number (step S40). In S40, when it is determined that it is not necessary to calculate the number of reactions, the measured value output unit 46 outputs the normal neutron fluence (step S50).

For example, when the number of reactions or the dose of grams of horses is required in the input unit 44 or when the number of reactions is set to be calculated, the number of reactions calculation unit 42 calculates the number of reactions (step S60). Next, the kema dose calculation unit 43 refers to the input information or setting status in the input unit 44 to determine whether it is necessary to calculate the kema dose (step S70). In S70, when it is determined that it is not necessary to calculate the kilogram dose, the measured value output unit 46 outputs the response amount (step S80). Thereafter, the measured value output unit 46 outputs the normal neutron fluence (step S50).

For example, in the case where the kilogram dose is requested in the input unit 44 or when the kilogram dose is set to calculate the kilogram dose, the kilogram dose calculation unit 43 calculates the kilogram dose (step S90). The measured value output unit 46 outputs the kilogram dose (step S100). Thereafter, the measured value output unit 46 outputs the normal neutron fluence (step S50). Furthermore, when both the number of reactions and the dose of grams of horses are required, the measured value output unit 46 outputs both the number of responses and the dose of grams of horses.

Next, referring to FIG. 5, the procedure for determining the calibration constant will be described. This sequence is performed before the neutron beam measuring device 100 is manufactured and the first measurement is performed. In addition, if the number of uses of the neutron beam measuring device 100 increases, the calibration constant may deviate from the optimal value for the detection unit 30 due to deterioration of the detection unit 30 or the like. Therefore, this sequence can also be performed at a timing such as regular maintenance of the neutron beam measuring apparatus 100.

First, the detection unit 30 is installed in the calibration field of the national standard (step S110). In this calibration field, the neutron beam is adjusted with sufficient accuracy, and the conventional neutron fluence becomes a known state. Moreover, the detection part 30 is arrange|positioned at the calibration point of a calibration field.

Next, the detection unit 30 measures the neutron count (step S120). Furthermore, the calculation of the calibration constant is performed (step S130). Among them, use the relationship of "calibration constant=(normal neutron fluence in calibration field (known))/(neutron count×correction coefficient in calibration field)" for calculation. In addition, the correction coefficient correction is based on the effects of the perturbation (strain, self-masking) of the detection unit 30, the direction dependence, the deviation from the 1/v cross-sectional area (Discrepancy), and the like. After the calibration constant is determined by the above sequence, it is input to the neutron beam measuring device.

Next, the conventional neutron fluence will be described in detail.

First of all, as a comparison object of conventional neutron fluence, the use of real thermal neutron fluence to measure neutron beams is explained. In the case of measuring the true thermal neutron fluence, it is necessary to cover the filter that cuts off the thermal neutron beam on the scintillator for the first measurement and not to cover the filter for the second measurement to calculate the difference between the two. In this way, since two measurements are required, the measurement takes time and effort, and the uncertainty of the measurement also increases.

The following equation (4) is the equation that defines the true thermal neutron fluence. Φ(E) in equation (4) represents the energy differential neutron fluence (neutron energy spectrum). Among them, when the number of reactions of the detection section 30 (the number of times the detection section 30 detects neutrons (=reactions with neutrons) within the measurement time) is set to R and the average cross-sectional area is set to σ _th , the formula (4 ) Is as shown in formula (5). That is, the true thermal neutron fluence is set to a value obtained by dividing the number of reactions as an indicator value of the detection unit 30 by the average cross-sectional area. The definitions of each item are as the following formula (6) and formula (7). The average cross-sectional area shown in formula (7) is the amount obtained by averaging the reaction cross-sectional area with energy differential neutron fluence. In this way, the evaluation of true thermal neutron fluence requires an average cross-sectional area, but the average cross-sectional area is a value that cannot be actually measured, so it is necessary to use the result of a simulation experiment. Among them, the determination of the standardization constant is a part of the verification of the calculation accuracy. In such an operation, the following is performed, that is, the average cross-sectional area is calculated based on the calculation result whose accuracy cannot be guaranteed, the actual measurement value is corrected by the average cross-sectional area, and the calculation accuracy is confirmed by the corrected measurement value. As a result, the uncertainty of the average cross-sectional area needs to be overestimated. In addition, the average cross-sectional area depends on the measurement depth, so it is necessary to adjust the average cross-sectional area to be used every time the measurement point is changed.

In contrast, when a 1/v detector is used for measurement, the conventional neutron fluence rate (the value obtained by dividing the conventional neutron fluence by the irradiation time (unit time) of the charged particle beam) does not depend on The average cross-sectional area is proportional to the neutron count. Therefore, the conventional neutron fluence can accurately express the amount of neutrons without being affected by the factors including the uncertainty of the average cross-sectional area. Specifically, the following formula (8) is the formula for defining the conventional neutron fluence. E ₀ conventionally takes a value of 0.0253 eV. Furthermore, in the case of using a 1/v detector, the conventional neutron fluence is simplified to the following equation (9). Here, R is represented by formula (6). Conventionally, σ ₀ is set as the value of the reaction cross-sectional area of the detection element with respect to the neutron with a velocity of 2200 m/s. It is clear from formula (5) and formula (9) that, compared with formula (5), which depends on the average cross-sectional area, formula (9) does not depend on the average cross-sectional area. Different from equation (5), equation (8) does not appear in items of average cross-sectional area.

Among them, the restriction conditions when using conventional neutron fluence are explained. First, in order to calculate the conventional neutron fluence with high accuracy, the detection unit 30 needs to be configured with a 1/v detector. This is because the above equation (9) holds true when a 1/v detector is used. The 1/v detector is a detector that uses a 1/v absorber in the scintillator 31. Among them, the 1/v absorber is a substance whose cross-sectional area decreases in proportion to 1/v in a region where ^{the incident energy of the neutron beam is 10 -4 MeV or less and where the incident energy is low.} Furthermore, the cross-sectional area here refers to the microscopic cross-sectional area. That is, the cross-sectional area is a measure of the proportion of nuclear reactions caused. When the reaction rate (the number of reactions per unit time) when a substance is exposed to a single-energy neutron field is set to R and the number density of the nuclei of the substance is set to N, the cross-sectional area is defined by equation (10). ϕ(E) is the neutron beam. The larger the cross-sectional area, the easier it is for the absorbent to react with neutrons. "V" represents the velocity of neutrons. When the mass of each neutron is set to m, v and the neutron energy E have the relationship shown in formula (11). The 1/v detector is a detector that uses the nucleus whose cross-sectional area is proportional to 1/v. The proportional relationship between σ and 1/v is established and the proportional relationship between v and E ^1/2 is established, so the proportional relationship between σ and 1/E ^1/2 is established. Therefore, when the energy of the horizontal axis is plotted during recording, the relationship between the cross-sectional area and linearity is shown in FIG. 6, and the slope becomes -1/2.

Examples of such 1/v absorbents include ¹⁰ B, ⁶ Li, ¹⁴ N, ³ He and the like. Specifically, as shown in the graph of Fig. 6 showing the characteristic of ¹⁰ B and the graph of Fig. 7 showing the characteristic of ⁶ Li, the cross-sectional area of the absorbers in the low incident energy region below ^{10 -4 MeV} Decrease in proportion to 1/v. Furthermore, in the high-energy region, the proportional relationship with 1/v is deviated. Therefore, in such a region, it is necessary to make corrections when calculating the conventional neutron fluence. On the other hand, as shown in the graph of Fig. 8 showing the characteristics of ^{197 Au, even in a region with a low incident energy of 10 -4} MeV or less, the cross-sectional area of the absorbent deviates from the proportional relationship of 1/v. Therefore, ^{absorbents such as 197} Au are not classified as 1/v absorbents.

Furthermore, with regard to the number of reactions and the Kema dose, values for predetermined atoms are calculated, but these atoms are limited to 1/v absorbents. This is because the above formulas (2) and (3) hold for the 1/v absorbent. Among them, in the treatment planning device 200 of BNCT, it is necessary to grasp the number of responses or the important atoms of the gamma dose are atoms belonging to ^{1/v absorbers such as 10} B, ¹⁴ N, etc. Therefore, for the treatment planning device 200, the limitation is It will not be very restrictive. Furthermore, the atom of the 1/v absorber used in the detection unit 30 and the atom to be the calculation object of the reaction number need not necessarily match. ^{For example, even if a 1/v absorbent other than 10} B is used in the detection unit 30, the reaction number calculation unit 42 can calculate the reaction number of ^{10 B.}

As described above, the 1/v absorber needs to be corrected in the high-energy region, but in order to reduce the amount of correction, it is better to measure in the water prosthesis 35 (see FIG. 2). In the case of measurements in air, the neutron field needs to be sufficiently heated. Therefore, the neutron beam measuring device 100 of the present embodiment is not suitable for the measurement of the superthermal neutron field. However, the standardization of the treatment planning device 200 is performed in the water prosthesis 35, so there is no particular problem with this restriction condition.

The detection head (part of the scintillator 31) of the detection unit 30 is small. Therefore, if the disturbance effect of the neutron field in the water (disturbance effect=strain effect×self-masking effect) is not small enough, the uncertainty based on the correction becomes larger. The disturbance effect is the effect caused by the presence of substances other than water at the measurement site. Specifically, it is better to suppress the strain effect and the self-shielding effect to a sufficiently small range of 1% or less.

Next, the function/effect of the neutron beam measuring device 100 of the present embodiment will be described.

The neutron beam measuring device 100 of the present embodiment measures the amount of the neutron beam N generated by irradiating the charged particle beam R to the target 10. The neutron beam measuring device 100 includes a detection unit 30 that detects the neutron beam N ; And the conventional neutron fluence calculation unit 41, which calculates the amount of neutron beam N based on the detection result of the detection unit 30, and the conventional neutron fluence calculation unit 41 calculates the conventional neutron fluence.

The neutron beam measuring device 100 includes a detection unit 30 that detects the neutron beam N; and a normal neutron fluence calculation unit 41 that calculates the amount of the neutron beam N based on the detection result of the detection unit 30. Among them, the conventional neutron fluence calculation unit 41 calculates the conventional neutron fluence. With the above, the measurement can be easily performed and the measurement accuracy can be improved. The conventional neutron fluence is different from the true thermal neutron fluence and does not depend on the average cross-sectional area with large uncertainty. Therefore, the uncertainty of measurement can be reduced. By reducing the uncertainty of measurement in this way, the uncertainty of the standardized constant in the treatment planning device 200 can also be reduced. In addition, the conventional neutron fluence can be calculated by one measurement without using a filter or the like, so it can be easily measured. With the above, the measurement of the neutron beam can be easily performed and the measurement accuracy can be improved.

In addition, according to the neutron beam measuring device 100, the calibration constant obtained according to the national standard is used, so that the obtained measurement value can ensure the traceability to the national standard.

In the neutron beam measuring device 100, the detection unit 30 is configured to include a 1/v detector. At this time, the conventional neutron fluence can depend on the neutron count value. Therefore, the uncertainty of measurement can be reduced.

The neutron beam measuring device 100 also has a display unit 60 for displaying information, and the display unit 60 displays the calculated conventional neutron fluence. Thereby, the normal neutron fluence can be grasped from the display unit 60, so the calculated normal neutron fluence can be effectively used.

In the neutron beam measuring device 100, the reaction number calculation unit 42 calculates the reaction number of a predetermined atom based on the conventional neutron fluence. Thereby, the number of reactions of specific atoms can be effectively used. In addition, 1/v absorbers other than ¹⁰ B can be used to obtain the number of reactions ^{of 10 B in the neutron field.}

In the neutron beam measuring device 100, the kema dose calculation unit 43 calculates the kema dose based on the number of reactions. In this way, the Kema dose can be effectively used. It is possible to obtain the Kema dose ^{of 10} B in the subfield as the most important information in neutron capture therapy. Furthermore, it is possible to use 1/v absorbers other than ¹⁰ B to obtain a Kema dose ^{of 10 B in the neutron field.}

The neutron beam measurement method of the present embodiment measures the amount of neutron beam N generated by irradiating a charged particle beam R to the target 10. The neutron beam measurement method includes: a detection step (S20), detecting the neutron beam N ; And the calculation step (S30), the amount of neutron beam N is calculated according to the measurement result of a measurement in the detection step, and the conventional neutron fluence is calculated in the calculation step.

According to the neutron beam measurement method of this embodiment, the same action/effect as the above-mentioned neutron beam measurement device 100 can be obtained.

The present invention is not limited to the above-mentioned embodiment.

In the above-mentioned embodiment, the calculation unit calculates the normal neutron fluence, but it can also calculate the normal neutron fluence rate. The conventional neutron fluence rate (conventional neutron flux) is the value obtained by dividing the conventional neutron fluence by the unit time. The conventional neutron fluence rate is a value that changes momentarily with the passage of time in a single irradiation. For example, when the unit time is set to 1 second, the calculation unit can output the normal neutron fluence rate every 1 second. That is, the neutron beam measuring device can measure the conventional neutron fluence rate in real time. In addition, the calculation unit can calculate the reaction rate and the Kema dose rate from the conventional neutron fluence rate. Through the above, the neutron beam measuring device can measure at least one of the conventional neutron fluence rate, reaction rate, and Kema dose rate in real time. At this time, the amount of neutron beam can be grasped in real time according to time.

In addition, in the neutron beam measuring device, the computing unit can calculate the conventional neutron fluence rate, the reaction rate, and the irradiation time of the charged particle beam by dividing at least one of the conventional neutron fluence, reaction number, and gamma dose by the irradiation time of the charged particle beam. The average of at least one of the Kema dose rates. The average value is the average of the entire irradiation time, so only one value can be obtained in a single irradiation. In this way, it is possible to grasp the amount of neutron beam over the entire irradiation time.

In addition, the calculation unit can directly calculate the conventional neutron fluence rate. For example, when the neutron count rate (count rate) is input from the measuring device 34, the normal neutron fluence rate can be calculated based on the count rate, the correction coefficient, and the calibration constant. The count rate is the value obtained by dividing the neutron count by the time required to obtain its count. As long as the count rate and time are obtained from the measuring device 34 and the regular neutron fluence rate and time are provided to the user, the user can calculate the regular neutron fluence by himself. In this way, the conventional neutron fluence rate does not need to be calculated through the conventional neutron fluence. The counting rate can also be considered for purposes other than real-time measurement every 1 second. As long as the average count rate (for example, 100000 counts per second) and the measurement time (100 seconds) for one measurement (for example, 100 seconds) are obtained to know the conventional neutron fluence rate (average value) in 100 seconds, you can borrow The conventional neutron fluence is calculated by multiplying this value by 100 seconds.

Furthermore, the present invention can use detectors other than scintillators. For example, as a detector for measuring the number of neutrons, a ^{proportional counter tube that uses a gas of 3} He and a proportional counter tube that vaporizes ^{10 B can be used.} The detection method is not particularly limited, but the type of counting neutrons is preferred.

For example, the above-mentioned neutron beam measuring device 100 has a response number calculation unit 42 and a koma dose calculation unit 43, but at least a conventional neutron fluence calculation unit 41 is required, and the reaction number calculation unit 42 and the koma dose calculation unit 43 may be omitted.

1: Neutron capture therapy device 10: Target 30: Inspection Department 41: Conventional Neutron Fluence Operation Department (Calculation Department) 42: Reaction number calculation unit (arithmetic unit) 43: Kema dose calculation department (calculation department) 60: Display 100: Neutron beam measuring device

Fig. 1 is a schematic diagram showing a neutron capture therapy device that generates a neutron beam to be the measurement target of the neutron beam measurement device of the embodiment of the present invention. [Figure 2] is a block diagram of the neutron beam measuring device. [Fig. 3] A graph showing the flux of neutron beams in a predetermined depth of a water phantom. [Fig. 4] is a flowchart showing the processing content of the neutron beam measurement method of this embodiment. [Figure 5] is a diagram showing the steps of determining the sequence of calibration constants. [Figure 6] is a graph showing the characteristics of ^{10 B.} [Figure 7] A graph showing the characteristics of ^{6 Li.} [Figure 8] is a graph showing the characteristics of ^{197 Au.}

1: Neutron capture therapy device

30: Inspection Department

31: scintillator

32: Optical fiber

33: Light detector

34: Measurer

35: Water prosthesis

40: Control Department

41: Conventional Neutron Fluence Operation Department

42: Reaction number calculation unit

43: Kema Dose Calculation Department

44: Input section

46: Measured value output section

60: Display

100: Neutron beam measuring device

200: Treatment planning device (user)

N: Neutron beam

Claims (8)

A neutron beam measuring device, which measures the amount of neutron beam generated by irradiating a charged particle beam to a target, the neutron beam measuring device is provided with: The detection unit detects the aforementioned neutron beam; and The calculation unit calculates the amount of the aforementioned neutron beam based on the detection result of the aforementioned detection unit, The aforementioned calculating unit calculates at least one of the conventional neutron fluence and the conventional neutron fluence rate. The neutron beam measuring device according to claim 1, wherein The aforementioned detection unit is configured to include a 1/v detector. The neutron beam measuring device according to claim 1 or claim 2, which further includes a display unit for displaying information, The aforementioned display unit displays at least one of the aforementioned regular neutron fluence and the aforementioned regular neutron fluence rate. The neutron beam measuring device as described in claim 1 or 2, wherein The aforementioned calculation unit calculates the predetermined number of reactions of atoms based on the aforementioned conventional neutron fluence. The neutron beam measuring device according to claim 4, wherein The aforementioned calculation unit calculates the kema dose based on the aforementioned response number. The neutron beam measuring device according to claim 1 or claim 2, which measures at least one of the aforementioned conventional neutron fluence rate, reaction rate, and Kema dose rate. The neutron beam measuring device as described in claim 1 or 2, wherein The aforementioned calculating unit calculates at least one of the aforementioned conventional neutron fluence rate, response rate, and gamma dose rate by dividing at least one of the aforementioned conventional neutron fluence, reaction number, and gamma dose by the irradiation time of the charged particle beam An average value. A neutron beam measurement method, which measures the amount of neutron beam generated by irradiating a charged particle beam to a target. The neutron beam measurement method has: The detection step is to detect the aforementioned neutron beam; and The calculation step is to calculate the amount of the aforementioned neutron beam based on the detection result in one measurement of the aforementioned detection step, In the foregoing calculation step, at least one of the conventional neutron fluence and the conventional neutron fluence rate is calculated.

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