JP2020159728A - Neutron beam detector - Google Patents

Abstract

To detect neutron beams with higher precision.SOLUTION: A neutron beam detector 100 for detecting neutron beams includes: a scintillator 13 that generates light when radiation is incident; a photodetector 15 that detects the light generated in the scintillator 13 as an optical signal; and a dose calculation section 21 that calculates a dose of a neutron beam from a signal of the neutron beam included in an optical signal detected by the photodetector 15. The dose calculation section 21 associates a wave height distribution based on the optical signal detected by the photodetector 15 with a wave height pattern related to a predetermined line type acquired in advance, and calculates the dose of the neutron beam according to the corresponding result.SELECTED DRAWING: Figure 3

Description

The present invention relates to a neutron beam detector.

There is a technique described in Patent Document 1 as a technique for discriminating between neutron rays and gamma rays. In the system according to Patent Document 1, the signal due to neutron rays and the signal due to gamma rays are discriminated from the peak height distribution of the detected signal. This system sets a predetermined determination threshold value and discriminates the detected signal whose wave height exceeds the determination threshold value as a signal related to a neutron beam.

International Publication No. 2014/192321

However, when the wave height of the gamma ray is higher than the judgment threshold value, the signal related to the gamma ray is also judged as the signal related to the neutron ray, and there is room for improvement in detecting the neutron beam accurately.

The present invention has been made in view of the above, and an object of the present invention is to provide a neutron beam detection device capable of calculating a neutron beam dose more accurately.

In order to achieve the above object, the neutron beam detection device according to one embodiment of the present invention is a neutron beam detection device that detects neutron rays, and includes a scintillator that generates light when radiation is incident on it and light generated by the scintillator. The dose calculation unit includes a photodetector that detects the light as an optical signal and a dose calculation unit that calculates a neutron beam dose from the neutron beam signal contained in the optical signal detected by the photodetector. , The wave height distribution based on the optical signal detected by the photodetector is associated with the wave height pattern related to a predetermined line type acquired in advance, and the dose of the neutron beam is calculated based on the associated result. ..

According to the above-mentioned neutron beam detection device, in the dose calculation unit, the wave height distribution based on the optical signal detected by the photodetector is made to correspond to the wave height pattern related to a predetermined line type, and the result is the result. The neutron dose is calculated based on this. Since the optical signal detected by the photodetector can predict the wave height pattern that will be detected for each line type, the neutron beam dose can be calculated using this pattern. The dose can be calculated more accurately.

The dose calculation unit acquires the wave height pattern related to the neutron beam in advance, and associates the wave height pattern related to the neutron beam with the wave height distribution based on the optical signal detected by the optical detector, and makes the correspondence. The dose of the neutron beam can be calculated from the wave height pattern related to the neutron beam.

As described above, by associating the wave height pattern related to the neutron beam with the wave height distribution based on the optical signal and calculating the dose of the neutron beam from the corresponding wave height pattern, among the optical signals related to multiple line types. The signal corresponding to the neutron beam can be specified more accurately, and the dose of the neutron beam can be calculated more accurately.

The dose calculation unit also acquires the wave height pattern related to the gamma ray in advance, and corresponds the wave height pattern related to the gamma ray and the wave height pattern related to the neutron ray to the wave height distribution based on the optical signal detected by the photodetector. The dose of the neutron beam can be calculated based on the result of the correspondence.

Photodetectors used in devices that irradiate neutrons can detect gamma rays and neutrons. Therefore, by acquiring the wave height patterns of these line types in advance and making them correspond to the wave height distribution based on the optical signal to calculate the neutron beam dose, the neutron beam dose can be obtained more accurately. Can be calculated.

The dose calculation unit refers to the wave height distribution based on the optical signal in a wave height region equal to or higher than the peak value of the signal related to the neutron beam included in the wave height distribution based on the optical signal or the neutron beam pattern. The wave height pattern related to the neutron beam can be matched.

In the wave height region above the peak value of the signal related to the neutron beam included in the wave height distribution based on the optical signal or the wave height pattern of the neutron ray, the ratio of signals related to other line types such as gamma rays is small. Therefore, by using these wave height regions to match the wave height patterns related to the neutron rays and calculating the dose of the neutron rays, the accuracy of the correspondence of the wave height patterns can be improved. The accuracy of dose calculation can also be improved.

The dose calculation unit calculates the wave height pattern related to the gamma ray from the corresponding wave height pattern related to the neutron ray, and subtracts the calculated wave height pattern related to the gamma ray from the wave height distribution based on the optical signal to obtain the neutron ray. It can be an aspect of calculating the dose.

The wave height pattern related to gamma rays can be calculated by using the wave height pattern related to the corresponding neutron rays. Therefore, the signal related to neutron rays can also be calculated by calculating the wave height pattern related to gamma rays and then subtracting it from the wave height distribution based on the optical signal to calculate the dose of neutron rays. Can be calculated accurately.

The dose calculation unit acquires the wave height pattern related to the gamma ray in advance, and in the wave height region from 0 to a predetermined wave height, the wave height related to the gamma ray is relative to the wave height distribution based on the optical signal detected by the photodetector. By matching the patterns and subtracting the matched wave height pattern from the wave height distribution based on the optical signal, the dose of the neutron ray can be calculated.

When the optical signal detected by the optical detector contains neutron rays and gamma rays, the crest height distribution based on the optical signal is associated with the gamma ray crest pattern, and then it is subtracted from the crest height distribution based on the optical signal. By calculating the dose of neutron rays, the signal related to the neutron rays can be calculated, and the dose of neutron rays can be calculated accurately.

According to the present invention, there is provided a neutron beam detection device capable of more accurately calculating a neutron beam dose.

FIG. 1 is a schematic diagram showing a neutron capture therapy system including the neutron beam detection device of one embodiment. FIG. 2 is a cross-sectional view showing a neutron beam detector provided in the collimator. FIG. 3 is a block diagram showing a neutron beam detector. 4 (a) to 4 (c) are diagrams showing an example of a graph relating to a procedure for calculating a neutron beam dose. It is a flow chart explaining the procedure at the time of calculating the dose of a neutron beam. It is a flow chart explaining the procedure at the time of calculating the dose of a neutron beam. 7 (a) and 7 (b) are diagrams showing an example of a graph relating to a procedure for calculating the dose of a neutron beam. 8 (a) to 8 (c) are diagrams showing an example of a graph relating to a procedure for calculating the dose of a neutron beam.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

The neutron capture therapy system 150 shown in FIG. 1 includes a neutron capture therapy device 1, a neutron beam detection device 100, a display unit 31, and an input unit 32. Here, first, the neutron capture therapy device 1 will be described. The neutron capture therapy device 1 is a device that performs cancer treatment using boron neutron capture therapy (BNCT). In the neutron capture therapy device 1, for example, the tumor of the patient (irradiated body) 50 to which boron ( ¹⁰ B) is administered is irradiated with neutron rays N.

The neutron capture therapy device 1 includes a cyclotron 2. The cyclotron 2 is an accelerator that accelerates charged particles such as anions to produce a charged particle beam R. In the present embodiment, the charged particle beam R is a proton beam generated by stripping an electric charge from an anion. The cyclotron 2 has the ability to generate a charged particle beam R having a beam radius of 40 mm and a beam radius of 60 kW (= 30 MeV × 2 mA), for example. The accelerator is not limited to the cyclotron, and may be a synchrotron, a synchrocyclotron, a linac, or the like.

The charged particle beam R emitted from the cyclotron 2 is sent to the neutron beam generator M. The neutron beam generation unit M includes a beam duct 3 and a target 7. The charged particle beam R emitted from the cyclotron 2 passes through the beam duct 3 and travels toward the target 7 arranged at the end of the beam duct 3. A plurality of quadrupole electromagnets 4, a current monitor 5, and a scanning electromagnet 6 are provided along the beam duct 3. The plurality of quadrupole electromagnets 4 use, for example, an electromagnet to adjust the beam axis of the charged particle beam R.

The current monitor 5 detects the current value (that is, charge, irradiation dose rate) of the charged particle beam R irradiated to the target 7 in real time. As the current monitor 5, a non-destructive DCCT (DC Current Transformer) capable of measuring current without affecting the charged particle beam R is used. The current monitor 5 outputs the detection result to the control unit 20 described later. The “dose rate” means the dose per unit time.

Specifically, in order to accurately detect the current value of the charged particle beam R irradiating the target 7, the current monitor 5 is downstream from the quadrupole electromagnet 4 (charged particle beam) in order to eliminate the influence of the quadrupole electromagnet 4. It is provided on the downstream side of R) immediately before the scanning electromagnet 6. That is, since the scanning electromagnet 6 scans the target 7 so that the charged particle beam R is not always irradiated in the same place, a large current monitor 5 is required to dispose the current monitor 5 on the downstream side of the scanning electromagnet 6. Is required. On the other hand, by providing the current monitor 5 on the upstream side of the scanning electromagnet 6, the current monitor 5 can be miniaturized.

The scanning electromagnet 6 scans the charged particle beam R and controls the irradiation of the charged particle beam R to the target 7. The scanning electromagnet 6 controls the irradiation position of the charged particle beam R with respect to the target 7.

The neutron capture therapy device 1 generates a neutron beam N by irradiating the target 7 with a charged particle beam R, and emits the neutron beam N toward the patient 50. The neutron capture therapy device 1 includes a target 7, a shield 9, a moderator 8, a collimator 10, and a gamma ray detection unit 11.

Further, the neutron capture therapy device 1 includes a control unit 20. The control unit 20 is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and is an electronic control unit that comprehensively controls the neutron capture therapy device 1. The detailed configuration of the control unit 20 will be described later.

The target 7 is irradiated with a charged particle beam R to generate a neutron beam N. The target 7 here is formed of, for example, beryllium (Be), lithium (Li), tantalum (Ta), and tungsten (W), and has, for example, a disk shape having a diameter of 160 mm. The target 7 is not limited to a disk shape and may have another shape. Further, the target 7 is not limited to a solid state but may be a liquid state.

The moderator 8 decelerates the energy of the neutron beam N generated by the target 7. The moderator 8 includes a first moderator 8A that mainly decelerates fast neutrons contained in the neutron beam N, and a second moderator 8B that mainly decelerates extrathermal neutrons contained in the neutron beam N. It has a laminated structure.

The shield 9 shields the generated neutron beam N and the gamma ray or the like generated by the generation of the neutron beam N so as not to be emitted to the outside. The shield 9 is provided so as to surround the moderator 8. The upper part and the lower part of the shield 9 extend to the upstream side of the charged particle beam R from the moderator 8, and the gamma ray detection unit 11 is provided in these extending portions.

The collimator 10 shapes the irradiation field of the neutron beam N, and has an opening 10a through which the neutron beam N passes. The collimator 10 is, for example, a block-shaped member having an opening 10a in the center.

The gamma ray detection unit 11 detects gamma rays generated from the neutron beam generation unit M by irradiation with the charged particle beam R in real time. As the gamma ray detection unit 11, a scintillator, an ionization chamber, and various other gamma ray detection devices can be adopted. In the present embodiment, the gamma ray detection unit 11 is provided around the target 7 on the upstream side of the charged particle beam R from the moderator 8.

The gamma ray detection unit 11 is arranged inside the upper part and the lower part of the shield 9 extending upstream of the charged particle beam R, respectively. The number of gamma ray detection units 11 is not particularly limited, and may be one or three or more. When three or more gamma ray detecting units 11 are provided, they can be provided at predetermined intervals so as to surround the outer circumference of the target 7. The gamma ray detection unit 11 outputs the gamma ray detection result to the control unit 20. The configuration may not include the gamma ray detection unit 11.

Next, the configuration of the neutron beam detection device 100 according to the present embodiment will be described with reference to FIGS. 2 and 3.

As shown in FIG. 2, the neutron beam detection device 100 includes a neutron beam detector 12 and a control unit 20. Further, the control unit 20 of the neutron beam detection device 100 is connected to the display unit 31 and the input unit 32.

The collimator 10 is provided with a neutron beam detector 12 for detecting a neutron beam N passing through the opening 10a of the collimator 10 in real time. At least a part of the neutron beam detector 12 is provided in the through hole 10b (through hole formed in the direction orthogonal to the opening 10a) formed in the collimator 10. The neutron beam detector 12 includes a scintillator 13, an optical fiber 14, and a photodetector 15.

The scintillator 13 is a phosphor that converts incident radiation (neutron rays N, gamma rays) into light. In the scintillator 13, the internal crystal is excited according to the dose of the incident radiation, and scintillation light is generated. The scintillator 13 is provided in the through hole 10b of the collimator 10 and is exposed to the opening 10a of the collimator 10. The scintillator 13 emits light when a neutron beam N or a gamma ray in the opening 10a is incident on the scintillator 13. The scintillator 13 ^may employ 6 Li glass scintillator, LiCAF ^{scintillator,} a plastic scintillator coated with 6 ^LiF, a 6 LiF / ZnS scintillators like.

The optical fiber 14 is a member that transmits light generated by the scintillator 13. The optical fiber 14 is composed of, for example, a bundle of flexible optical fibers. The photodetector 15 detects the light transmitted through the optical fiber 14. As the photodetector 15, various photodetectors such as a photomultiplier tube and a phototube can be adopted. The photodetector 15 outputs an electric signal (detection signal) to the control unit 20 at the time of light detection.

The display unit 31 is a device that displays various information to the user. A display or the like is adopted as the display unit 31. When there is information that the user wants to input, the display unit 31 displays a notification that guides the user to input the information. In addition, the display unit 31 displays the result calculated by the control unit 20 in response to the input of the user. The display unit 31 displays the wave height distribution of the detection signal of the neutron beam detector 12. The input unit 32 is a device in which various inputs are made by the user. The input unit 32 is composed of a keyboard, a mouse, a touch screen, and the like.

As shown in FIG. 3, the control unit 20 includes a dose calculation unit 21, a wave height pattern information holding unit 23, and an irradiation control unit 22. The control unit 20 is electrically connected to a current monitor 5, a scanning electromagnet 6, a gamma ray detection unit 11, a photodetector 15 (neutron beam detector 12), a display unit 31, and an input unit 32.

The dose calculation unit 21 measures (calculates) the dose of the charged particle beam R irradiated to the target 7 in real time based on the detection result of the current value of the charged particle beam R by the current monitor 5. The dose calculation unit 21 sequentially integrates the measured current value of the charged particle beam R with respect to time, and calculates the dose of the charged particle beam R in real time.

Further, the dose calculation unit 21 measures (calculates) the gamma ray dose in real time based on the gamma ray detection result by the gamma ray detection unit 11.

Further, the dose calculation unit 21 measures (calculates) the dose of the neutron beam N passing through the opening 10a of the collimator 10 based on the detection result of the neutron beam N by the neutron beam detector 12. The dose calculation unit 21 receives the detection signal from the photodetector 15 and discriminates between the signal related to neutron rays and the signal related to gamma rays (details will be described later). The photodetector 15 and the dose calculation unit 21 constitute a discrimination unit.

The dose calculation unit 21 comprehensively calculates the dose of the neutron beam N generated at the target 7 in real time based on the calculated dose of the charged particle beam R, the dose of the gamma ray, and the dose of the neutron beam N. The calculation result by the dose calculation unit 21 such as the dose of the neutron beam N is displayed on the display unit 31, for example.

The wave height pattern information holding unit 23 has a function of holding wave height pattern information used for calculating the dose of the neutron beam N in the dose calculation unit 21. The wave height pattern information is information corresponding to the wave height pattern of the signal relating to the neutron beam and / or the signal relating to the gamma ray that receives the detection signal that can be detected by the photodetector 15. This wave height pattern information is information acquired in advance by the neutron beam detection device 100. The dose calculation unit 21 uses this wave height pattern information to discriminate the signal related to the neutron beam N from the signal actually detected by the photodetector 15 and calculate the dose. Details of the dose calculation by the dose calculation unit 21 based on the information held by the wave height pattern information holding unit 23 will be described later.

The irradiation control unit 22 controls the irradiation of the charged particle beam R to the target 7 based on the dose of the neutron beam N calculated by the dose calculation unit 21. The irradiation control unit 22 transmits a command signal to the cyclotron 2 and the scanning electromagnet 6 to control the irradiation of the charged particle beam R to the target 7, thereby controlling the irradiation of the patient with the neutron beam N generated from the target 7. .. The irradiation control unit 22 controls the irradiation of the neutron beam N so that the dose of the neutron beam N calculated by the dose calculation unit 21 conforms to a preset treatment plan.

Next, the calculation of the dose by the dose calculation unit 21 based on the information held by the wave height pattern information holding unit 23 will be described.

The dose calculation unit 21 describes the wave height (light amount) of the detection signal related to the light received by the photodetector 15, based on the information held by the wave height pattern information holding unit 23, the detection signal by the neutron beam N and the detection signal by the gamma ray. And the dose of neutron beam N is calculated. Since neutron rays N and gamma rays are incident as radiation in the scintillator 13, the neutron rays N and gamma rays are discriminated according to the intensity of the amount of light.

FIG. 4A is a graph showing the wave height distribution of the detection signal when the neutron beam detection device 100 is normal. In FIG. 4A, the horizontal axis shows the wave height (light amount) of the detection signal related to the light received by the photodetector 15, and the vertical axis shows the number of events (Count / s) of the detection signal. FIG. 4A shows the detection result V1 in the photodetector 15. The detection result V1 by the photodetector 15 includes a signal derived from gamma rays and a signal derived from neutron rays N.

However, how much each of the gamma ray and the neutron ray can theoretically be detected by the photodetector 15 can be obtained as a mathematical formula. That is, when the gamma ray and the neutron beam are irradiated under a certain ideal condition, the wave height distribution of the gamma ray or neutron beam detection signal that can be detected by the photodetector 15 can be obtained in advance. Therefore, in the neutron beam detection device 100 according to the present embodiment, the wave height distribution under this ideal condition is maintained as a gamma ray or neutron ray height pattern, and the components of the gamma ray and the neutron ray are specified based on this. Calculate the dose of neutron rays.

Further, in the neutron capture therapy system 150, it is possible to measure only gamma rays by using the neutron beam detection device 100. For example, in the neutron beam detection device 100, a filter that cuts the neutron beam N may be provided in front of the scintillator 13 so that the neutron beam N does not enter the scintillator 13. With such a configuration, only gamma rays are incident on the scintillator 13, and only the signal related to the gamma rays can be detected by the photodetector 15. In this case, since a wave height pattern consisting of only signals related to gamma rays can be obtained, this can be used as wave height pattern information related to gamma rays. As the filter, lithium fluoride, cadmium or the like can be used.

A method of calculating the dose of the neutron beam N from the wave height distribution obtained by the photodetector 15 using the wave height pattern information will be described with reference to FIGS. 4 to 8. First, a case where wave height pattern information related to gamma rays is used will be described with reference to FIGS. 4 and 5.

FIG. 5 is a flow chart illustrating a procedure for calculating the dose of the neutron beam N using the wave height pattern information related to the gamma ray. First, the wave height distribution is measured by the measurement by the photodetector 15 (step S01). The measurement by the photodetector 15 is the same as the usual method.

The dose calculation unit 21 subtracts the gamma ray component from the wave height distribution obtained by the photodetector 15 by using the wave height pattern information related to the gamma rays held by the wave height pattern information holding unit 23. At this time, the wave height pattern information related to the gamma rays is fitted to the wave height distribution obtained by the photodetector 15 (step S02). Fitting is a process of associating a wave height pattern so as to overlap with the wave height distribution. An example of a wave height pattern that fits the wave height distribution is shown in FIG. 4 (b).

As described above, the wave height pattern information related to gamma rays held by the wave height pattern information holding unit 23 is, for example, a wave height pattern or neutrons that can be acquired by the photodetector 15 when measurement is performed under ideal conditions. It is a wave height pattern obtained by performing measurement with a photodetector 15 in a state where the line N is blocked. Further, it has been found that the wave height distribution (curve shape) detected by the photodetector 15 can change significantly depending on the irradiation conditions of neutron rays and the like. Therefore, there is a high possibility that there is a difference from the result detected by the photodetector 15 when the neutron capture therapy system 150 actually irradiates the neutron beam N. This point is the same for gamma rays and neutron rays.

Therefore, the dose calculation unit 21 selects a region of a specific wave height from the wave height distribution obtained by the photodetector 15 as a region of interest (ROI), and fits the wave height pattern in the region. FIG. 4A shows an example in which a region R1 having a low wave height is selected as an example of the region of interest ROI. Further, FIG. 4A shows a wave height pattern P1 related to gamma rays. The wave height pattern P1 of gamma rays can be described as, for example, the mathematical formula _pg (x). The fitting of the wave height pattern includes, for example, adjusting the number of events in the vertical axis direction so that the detection result V1 and the wave height pattern P1 match in the region R1. That is, there is a method of determining the coefficient a so that the af _g (x) using the coefficient a matches the detection result V1 in the region R1. Further, for example, the peak of the detection result V1 on the low wave height side may be corrected so as to match the wave height pattern P1 of the gamma ray. As described above, the fitting method is not particularly limited, and a known fitting method can be used. When the wave height pattern obtained by performing the measurement with the photodetector 15 in a state where the neutron beam N is blocked is used as the wave height pattern information, the processing (S02) related to the fitting may be omitted.

In addition, various methods can be selected as the method for setting the ROI (region R1 in the example shown in FIG. 4) to be fitted. When fitting the gamma ray wave height pattern P1 to the detection result V1, the ROI is often selected as a region on the low wave height side where the neutron ray detection result is unlikely to appear. In the case of fitting related to the wave height pattern of gamma rays, the lower limit of the wave height of ROI may be 0. Further, the lower limit of the wave height of the ROI can be, for example, the wave height at which the peak on the low wave height side appears in the wave height detection result V1 (when the wave height is shown as a histogram, the peak on the low wave height side is the lowest wave height side. A bin containing a wave height of 0 often appears). The upper limit of the ROI wave height is, for example, a predetermined ratio (for example, 1/4, etc.) to the wave height at which the neutron beam peak (in the case of the example of FIG. 4A, the peak appearing on the high wave height side) appears. The wave height may be set as the upper limit. Further, a predetermined value (for example, 50 keV or the like) may be set in advance for the upper limit of the wave height of the ROI. In this way, which region (wave height width) is set as the ROI can be appropriately changed.

Returning to FIG. 5, after fitting (S02) is performed, the dose calculation unit 21 subtracts the wave height pattern of the gamma ray after fitting from the detection result V1 of the wave height distribution (step S03). As a result, the number of events at each wave height included in the gamma ray wave height pattern after fitting is subtracted from the detection result V1. The deducted result is shown as a deducted result V2 in FIG. 4 (c). After that, the dose calculation unit 21 calculates the count number of the signal related to the neutron beam N by integrating the wave height distribution obtained after the subtraction (step S04). The dose calculation unit 21 integrates the counts included in the deduction result V2 shown in FIG. 4C to calculate the count number of the signal related to the neutron beam N. As a result, the dose calculation unit 21 can calculate the dose related to the neutron beam N.

Next, a case where the wave height pattern information related to the neutron beam is used will be described with reference to FIGS. 6 and 7.

FIG. 6 is a flow chart illustrating a procedure for calculating the dose of the neutron beam N using the wave height pattern information related to the neutron beam. First, the wave height distribution is measured by the measurement by the photodetector 15 (step S11). The measurement by the photodetector 15 is the same as the usual method.

The dose calculation unit 21 fits the wave height pattern information related to the neutron beam held by the wave height pattern information holding unit 23 to the wave height distribution obtained by the photodetector 15 (step S12). FIG. 7 shows an example of a state in which the wave height pattern related to the neutron beam is fitted to the wave height distribution obtained as the detection result.

The dose calculation unit 21 selects a region of a specific wave height from the wave height distribution obtained by the photodetector 15 as a region of interest (ROI), and fits a neutron beam height pattern in that region. In the neutron capture therapy system 150, it is not possible to measure only the neutron beam using the neutron beam detection device 100. Therefore, the wave height pattern information of the neutron beam used for fitting is when the measurement is performed under ideal conditions. This is information related to a wave height pattern that can be acquired by the photodetector 15. In the case of fitting a neutron wave height pattern, a region R2 having a high wave height can be selected as an example of the region of interest ROI. As shown in FIG. 4 (b), in the gamma ray wave height distribution, the number of signals decreases in the region where the wave height is high. In particular, in a region where the wave height is higher than the peak of the wave height of the neutron beam (the peak at the wave height x ₀ shown in FIG. 7), the wave height of the gamma ray becomes close to 0. Therefore, when fitting the wave height pattern of the neutron beam, a region having a wave height higher than the wave height corresponding to the peak of the wave height of the neutron beam can be set as the region of interest ROI. The wave height x ₀ may be set based on the wave height pattern P2 of the neutron beam acquired in advance, or may be set based on the detection result V1.

FIG. 7 shows the detection result V1 and the neutron beam height pattern P2. The wave height pattern P2 is corrected so that these two curves coincide with each other in the region R2. That is, when the wave height is x, the wave height distribution of the detection result is f _means (x), and the neutron beam height pattern P2 is f _n (x), the following mathematical formula (1) is satisfied when x> x ₀ . The coefficient b will be obtained.
f _means (x) = bf _n (x) ... (1)

The fitting method is not particularly limited as in the fitting of the wave height pattern of gamma rays, and a known fitting method can be used. In addition, the peak of the wave height in the detection result V1 and the peak of the wave height in the wave height pattern P2 of the neutron beam may be different from each other. In this case, correction or the like for shifting the wave height in the horizontal axis direction may be performed so that the peak positions match. Further, when the peak shape of the neutron beam in the neutron beam detection result V1 changes with respect to the wave height pattern P2 due to a change in the characteristics of the photodetector 15, the above coefficient b is set with respect to the wave height pattern P2. Fitting may be performed by applying not only such a correction but also another fitting function (shape function) or the like. For example, the wave height distribution due to neutron rays may be approximated to the gown distribution by a linear function. When performing approximation using such a complicated function, there are a plurality of parameters (coefficients) obtained by fitting.

Various methods can be selected as the method for setting the ROI (region R2 in the example shown in FIG. 7) to be fitted. In the above, the region R2 that becomes the ROI is defined as a region where the wave height is higher than the peak of the wave height of the neutron beam (the peak at the wave height x ₀ shown in FIG. 7), but the wave height is not limited to this, and for example, the number of events (signal). The region where the number) is small may be excluded from the ROI. Which region (wave height width) is set as the ROI can be appropriately changed.

Returning to FIG. 6, after the fitting (S12) is performed, the dose calculation unit 21 integrates the wave height pattern of the neutron beam after the fitting to calculate the neutron count number (step S13). From the above fitting (S12), the mathematical formula bf _n (x) related to the wave height pattern of the neutron beam can be specified. Therefore, the neutron count can be obtained by integrating the mathematical formula related to this wave height pattern as shown in the following mathematical formula (2).

In this way, the count number of neutrons can be calculated by integrating the mathematical formula after fitting, and the dose calculation unit 21 can calculate the dose related to the neutron beam N. The above formula (2) is an example. For example, when fitting using a complicated function, the formula corresponding to the fitting result is input to the right side.

In the above method, the mathematical formula bf _n (x) related to the wave height pattern of the neutron beam is specified, and the count number of the neutron beam is calculated by integrating this. In this case, it was obtained by measurement. Statistical errors (noise) contained in the crest distribution are ignored. As a method for solving this point, the method described below may be used.

Specifically, after fitting the neutron beam pattern to obtain the coefficient b, bf _n (x) is subtracted from the wave height distribution f _means (x) obtained from the photodetector. The mathematical formula (3) obtained by this is a wave height distribution by gamma rays.
f _g (x) = f _means (x) -bf _n (x) ... (3)

The wave height distribution _fg (x) due to the obtained gamma rays is smoothed. Since the gamma ray wave height is close to 0 in the region R2 that becomes the ROI, the smoothed gamma ray wave height distribution _pg (x) should be zero in the region R2.

By the above procedure, a gamma ray wave height pattern can be substantially obtained. Therefore, similarly to the procedure shown in step S03 and step S04 of FIG. 5, the count number of neutrons is calculated by subtracting the above gamma ray wave height pattern from the measured wave height distribution and then integrating the wave height distribution. Can be done.

As described above, after fitting the neutron pattern, the wave height pattern related to the gamma ray may be calculated, and the neutron count may be calculated using this.

In FIGS. 4 to 7 described above, the case where either the gamma ray wave height pattern information or the neutron ray wave height pattern information is used has been described, but the neutron ray count may be calculated using both of them. In that case, the count number of neutron rays can be obtained by combining the procedures described above.

FIG. 8 shows a graph relating to a procedure when both gamma ray wave height pattern information and neutron ray wave height pattern information are used. FIG. 8A shows a gamma ray wave height pattern P1. This wave height pattern P1 can be described as, for example, y = f _g (x). On the other hand, FIG. 8B shows a neutron beam height pattern P2. This wave height pattern P2 can be described as, for example, y = f _n (x).

Using these two wave height patterns P1 and P2, fitting is performed on the detection result V1 obtained by the photodetector 15. In this case, when the wave height distribution of the detection result is _fmeans (x), the coefficients a and b satisfying the following mathematical formula (4) are obtained.
f _means (x) = af _g (x) + bf _n (x)… (4)

In FIG. 8 (c), af _g (x) + bf _n (x) after fitting is shown as a wave height pattern P3. At the time of fitting, the coefficients a and b are calculated so that the detection result V1 and the wave height pattern P3 match.

After the fitting is performed, the dose calculation unit 21 integrates the wave height pattern of the neutron beam after the fitting to calculate the count number of neutrons. Since the mathematical formula bf _n (x) related to the neutron beam height pattern can be specified by the above fitting, the mathematical formula related to this wave height pattern is integrated as shown in the following mathematical formula (2) described above. You can get the neutron count with. Further, when the fitting is performed with high accuracy, the relationship of the following mathematical formula (5) holds, so that the count number of neutron rays can be obtained by using the detection result V1 and the wave height pattern P1 after the fitting.

Whether to calculate the neutron count number using the neutron beam height pattern P2 after fitting or to calculate the neutron ray count number using the detection result V1 and the gamma ray wave height pattern P1 after fitting is appropriately selected. can do. For example, neutrons in consideration of how accurately the fitting could be performed, or how much the measurement conditions fluctuate compared to the gamma-ray / neutron irradiation conditions when the wave height pattern is calculated. It is considered that the method of calculating the number of line counts can be selected.

Even when both the gamma-ray and neutron-ray wave height pattern information is used, the fitting method and the like can be appropriately changed as in the case of using only the neutron-ray wave height pattern described above. Further, in FIG. 8, the fitting is performed in all the wave height regions, but the fitting may be performed by designating the ROI. In that case, the wave height region to be the ROI can be appropriately changed based on the measurement conditions and the like.

As described above, according to the neutron beam detection device 100 according to the present embodiment, the wave height pattern related to the neutron beam N is made to correspond to the wave height distribution based on the optical signal detected by the photodetector 15. The dose of neutron beam N is calculated from the wave height pattern. With such a configuration, the signal corresponding to the neutron beam can be specified more accurately from the optical signals related to the plurality of line types, and the dose of the neutron beam can be calculated more accurately.

Further, the photodetector 15 used in the device that irradiates the neutron beam N can detect the gamma ray and the neutron beam. Therefore, as described in FIG. 8 and the like, the wave height patterns of these line types are acquired in advance, and these are made to correspond to the wave height distribution based on the optical signal to calculate the dose of the neutron beam N. Therefore, the dose of the neutron beam N can be calculated more accurately.

Further, in the wave height region equal to or higher than the peak value of the signal related to the neutron beam included in the wave height distribution based on the optical signal or the wave height pattern of the neutron ray, the ratio of the signal related to other line types such as gamma ray is small. Therefore, the wave height pattern is calculated by associating the wave height patterns related to the neutron rays with the regions where the wave height is larger than the peak value wave height, such as the above-mentioned region R2. Since the accuracy of the correspondence can be improved, the calculation accuracy of the neutron beam dose can also be improved.

In addition, the neutron dose is calculated by calculating the wave height pattern related to gamma rays from the corresponding wave height pattern related to neutron rays and subtracting the calculated wave height pattern related to gamma rays from the wave height distribution based on the optical signal. May be good. In this way, the signal related to neutron rays can also be calculated by calculating the wave height pattern related to gamma rays and then subtracting it from the wave height distribution based on the optical signal to calculate the dose of neutron rays. The dose can be calculated accurately. In addition, the neutron beam can be calculated in consideration of statistical errors.

Further, as described in the above embodiment, when the optical signal detected by the photodetector 15 includes neutron rays N and gamma rays, the wave height pattern of the gamma rays is associated with the wave height distribution based on the optical signals. After that, the signal related to the neutron ray can also be calculated by subtracting it from the wave height distribution based on the optical signal to calculate the dose of the neutron ray N. Even with such a configuration, the neutron beam dose can be calculated accurately.

The present invention is not limited to the above-described embodiment, and various modifications as described below are possible without departing from the gist of the present invention.

For example, in the above embodiment, the case where the wave height pattern information holding unit 23 holds the wave height pattern information used for fitting has been described. However, the wave height pattern information holding unit 23 does not have to be included in the control unit 20. For example, when calculating the neutron beam dose, the wave height pattern information is acquired from an external device or the like each time, and the above It may be configured to calculate the dose.

Further, a plurality of wave height pattern information used for fitting may be prepared for each line type. For example, if the neutron beam dose (target dose) or irradiation conditions used in the neutron capture therapy system 150 changes, the wave height distribution detected by the photodetector 15 of the neutron beam detector 100 may also change. In consideration of this point, a plurality of wave height patterns related to each line type may be prepared, and appropriate wave height pattern information may be selected and fitted according to conditions and the like.

For example, the arrangement of the neutron beam detection device 100 can be changed as appropriate. For example, the place where the scintillator 13 is arranged is not limited to the collimator 10 and may be another place. The scintillator may be arranged, for example, downstream of the collimator 10 or may be arranged on the surface of the patient (near the irradiated portion).

Further, in the above embodiment, the neutron beam detection device is applied to the neutron capture therapy device 1, but the use of the neutron beam detection device is not limited. For example, the neutron beam detection device of the present invention may be applied as a monitor for monitoring the operating state of a nuclear reactor. Further, the neutron beam detection device of the present invention may be used when measuring the accelerated neutron used in the physical experiment. Further, the neutron beam detection device of the present invention may be used in the neutron irradiation device for non-destructive inspection.

1 ... Neutron capture therapy device, 12 ... Neutron beam detector, 13 ... Scintillator, 14 ... Optical fiber, 15 ... Photodetector, 20 ... Control unit, 21 ... Dose calculation unit, 23 ... Wave height pattern information holding unit, 100 ... Neutron Photodetector, 150 ... Neutron capture therapy system, N ... Neutron beam.

Claims (6)

A neutron beam detector that detects neutron beams.
A scintillator that generates light when radiation is incident,
A photodetector that detects the light generated by the scintillator as an optical signal,
A dose calculation unit for calculating a neutron beam dose from a neutron beam signal included in the optical signal detected by the photodetector is provided.
The dose calculation unit associates a wave height pattern related to a predetermined line type acquired in advance with a wave height distribution based on the optical signal detected by the photodetector, and the neutron beam is based on the result of the correspondence. A neutron beam detector that calculates the dose of The dose calculation unit acquires the wave height pattern related to the neutron beam in advance, and associates the wave height pattern related to the neutron beam with the wave height distribution based on the optical signal detected by the optical detector, and makes the correspondence. The neutron beam detection device according to claim 1, wherein the dose of the neutron beam is calculated from a wave height pattern related to the neutron beam. The dose calculation unit also acquires the wave height pattern related to the gamma ray in advance, and corresponds the wave height pattern related to the gamma ray and the wave height pattern related to the neutron ray to the wave height distribution based on the optical signal detected by the photodetector. The neutron ray detection device according to claim 2, wherein the dose of the neutron ray is calculated based on the result of the correspondence. The dose calculation unit refers to the wave height distribution based on the optical signal in a wave height region equal to or higher than the peak value of the signal related to the neutron beam included in the wave height distribution based on the optical signal or the neutron beam pattern. The neutron beam detection device according to claim 2, which corresponds to a wave height pattern related to a neutron beam. Claim that the dose of the neutron ray is calculated by calculating the wave height pattern related to the gamma ray from the corresponding wave height pattern related to the neutron ray and subtracting the calculated wave height pattern related to the gamma ray from the wave height distribution based on the optical signal. 2. The neutron ray detection device according to 2. The dose calculation unit acquires the wave height pattern related to the gamma ray in advance, and in the wave height region from 0 to a predetermined wave height, the wave height related to the gamma ray is relative to the wave height distribution based on the optical signal detected by the photodetector. The neutron ray detection device according to claim 1, wherein the dose of the neutron ray is calculated by matching the patterns and subtracting the corresponding wave height pattern from the wave height distribution based on the optical signal.

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