Radiation detector

Abstract

To provide a radiation detector capable of detecting an accumulated radiation dose and a dynamic radiation dose while having little influence on an inspection.SOLUTION: A radiation detector 2 according to one embodiment includes: a photostimulated luminescence element 16; and a photodetector 18 for detecting light emitted from the photostimulated luminescence element 16 when radiation is incident on the photostimulated luminescence element 16. Preferably, the photostimulated luminescence element 16 and the photodetector 18 are laminated. Preferably, the radiation detector 2 further includes a light-shielding material 12 covering the photostimulated luminescence element 16 and the photodetector 18.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This specification discloses a radiation detector. [Background technology]

[0002] In medical settings, radiation-generating devices such as X-ray machines and CT scanners are used. Radiation exposure doses are controlled by law for radiation workers. Even for patients who are not subject to such legal control, it is important to understand their radiation exposure doses from the perspective of preventing health damage and alleviating concerns about radiation exposure.

[0003] Representative radiation dose measurement devices include active dosimeters and integrating dosimeters. Active dosimeters are used to measure the current radiation dose (herein referred to as dynamic radiation dose) in real time, and examples thereof include ionization chamber dosimeters and semiconductor dosimeters. Integrating dosimeters are used to measure the integrated amount of radiation received within a predetermined period, and examples thereof include glass badges and luminesce badges.

[0004] One type of integrating dosimeter is the Lumines Badge, which incorporates an optically stimulated luminescence element (called an OSL element). When radiation is incident on an OSL element, electrons and holes are generated internally. Some of these electrons and holes are trapped internally, resulting in a metastable state. When strong visible light is irradiated onto the OSL element in this state, the trapped electrons and holes recombine and emit light. The amount of light emitted is proportional to the integrated amount of radiation irradiated onto the OSL element. By measuring this amount of light emitted, the integrated amount of radiation to which the OSL element was exposed can be obtained. An example of a dosimeter using an OSL element is disclosed in JP 2014-081288 A. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-081288 A Summary of the Invention [Problem to be solved by the invention]

[0006] To understand the patient's condition when irradiated with radiation and improve the accuracy of measuring radiation dose, it is desirable to be able to measure not only the cumulative radiation dose but also the dynamic radiation dose in real time. However, when conventional cumulative and active dosimeters are attached to the patient, they can interfere with the examination. For example, the size of the dosimeter or the metal it contains can sometimes prevent accurate CT images from being obtained. There is a need for a radiation detector that can detect cumulative and dynamic radiation doses while minimizing the impact on the examination.

[0007] The present inventors have an intention to provide a radiation detector that can detect cumulative radiation dose and dynamic radiation dose and has little effect on the examination. [Means for solving the problem]

[0008] A radiation detector according to one embodiment includes a photostimulated luminescence element and a photodetector that detects light emitted from the photostimulated luminescence element when radiation is incident on the photostimulated luminescence element. [Effects of the Invention]

[0009] The inventors noticed that when radiation is incident on an OSL element, some of the electrons and holes generated immediately recombine and emit light without being trapped inside, leading to the idea that by detecting this light, the OSL element can be used to detect dynamic radiation dose in real time.

[0010] In this radiation detector, the photodetector detects the light emitted from the OSL element when radiation is incident on it. From this detection result, dynamic radiation dose can be measured. In addition, this radiation detector can measure the cumulative radiation dose by analyzing the OSL element with conventional reading equipment. Because this radiation detector uses the OSL element for both cumulative and dynamic radiation dose measurement, it can be made smaller than conventional detectors. This radiation detector has little impact on medical images. This radiation detector makes it possible to measure cumulative and dynamic radiation dose while minimizing the impact on examinations. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing a dosimetry system including a radiation detector according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the radiation detector of FIG. [Figure 3] FIG. 3 is a graph showing an example of the detection result of the radiation detector of FIG. [Figure 4] 4(a) and (b) are graphs showing other examples of the detection results of the radiation detector of FIG. [Figure 5] FIG. 5(a) is an example of a CT image including the radiation detector of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0013] FIG. 1 is a schematic diagram showing a radiation dosimetry system 4 including a radiation detector 2 according to one embodiment. This dosimetry system 4 is intended for measuring radiation exposure doses in medical settings, but its use is not limited to this. The dosimetry system 4 includes the radiation detector 2, a power supply 6, a processor 8, an output device 10, and a reader 11. FIG. 1 also shows radiation 20 incident on the radiation detector 2. Typical examples of the radiation 20 include X-rays, gamma rays, and beta rays. The radiation 20 may also be alpha rays or neutron rays.

[0014] The radiation detector 2 can measure both the amount of radiation currently being received (dynamic radiation dose) and the cumulative amount of radiation received to date (cumulative radiation dose). Figure 2 is a schematic diagram showing the structure of the radiation detector 2. The radiation detector 2 includes a first light-shielding material 12a, a reflector 14, an optically stimulated luminescence element 16 (OSL element 16), a photodetector 18, a second light-shielding material 12b, a first electrode 22, and a second electrode 24. The radiation detector 2 has a structure in which the first light-shielding material 12a, the reflector 14, the OSL element 16, the photodetector 18, and the second light-shielding material 12b are layered in this order. Although not visible in the figure, the first electrode 22 and the second electrode 24 are connected to the photodetector 18.

[0015] OSL elements 16 have traditionally been used to measure cumulative radiation doses. When radiation 20 is incident on OSL element 16, electrons and holes are generated inside. Some of these electrons are captured by ion defects, and some of the holes are captured by impurities, and they are maintained in this state. When radiation 20 is incident on OSL element 16 multiple times, some of the electrons and holes are captured inside each time. OSL element 16 captures electrons and holes in amounts corresponding to the cumulative amount of radiation 20 it has been exposed to so far.

[0016] On the other hand, some of the electrons and holes generated when radiation 20 is incident on OSL element 16 are not captured but immediately recombine to emit light. That is, in OSL element 16, electrons and holes are generated when radiation 20 is incident, some of these electrons and holes are captured internally, and the remaining electrons and holes recombine to emit light. In this embodiment, OSL element 16 is α-aluminum oxide (α-Al2O3). Other OSL elements 16, such as BeO, may also be used.

[0017] The photodetector 18 detects light from the OSL element 16 and converts it into an electrical signal. The photodetector 18 is connected to the power supply 6 via a first electrode 22 and to the processor 8 via a second electrode 24. The detection result of the photodetector 18 is sent to the processor 8. The photodetector 18 is stacked on the OSL element 16. In this embodiment, the photodetector 18 and the OSL element 16 are in contact with each other. The photodetector 18 and the OSL element 16 do not have to be in contact with each other. In this embodiment, the photodetector 18 is a multi-pixel photon counter (MPPC). The photodetector 18 may be any other photodetector 18.

[0018] The reflector 14 is used to allow the light generated by the OSL element 16 to efficiently enter the photodetector 18. The reflector 14 reflects the light from the OSL element 16 and returns it to the photodetector 18. The reflector 14 is laminated on the OSL element 16. The reflector 14 is located between the first light-shielding material 12a and the OSL element 16. In addition to being located between the first light-shielding material 12a and the OSL element 16, the reflector 14 may also be located between the second light-shielding material 12b and the photodetector 18. The material of the reflector 14 may be any material that transmits radiation 20 and reflects light. A preferred material for the reflector 14 is a resin composition that reflects light. In this embodiment, the material of the reflector 14 is a fluororesin.

[0019] The first light-shielding material 12a and the second light-shielding material 12b prevent external light from reaching the photodetector 18. In this embodiment, the first light-shielding material 12a and the second light-shielding material 12b sandwich the OSL element 16, the photodetector 18, and the reflector 14 from above and below. Although not clearly depicted in FIG. 2 for ease of viewing, the first light-shielding material 12a and the second light-shielding material 12b also cover the side surfaces of the OSL element 16 and the photodetector 18. The first light-shielding material 12a and the second light-shielding material 12b entirely cover the OSL element 16 and the photodetector 18. The first light-shielding material 12a and the second light-shielding material 12b may be made of any material as long as it transmits radiation 20 and blocks light. A preferred material for the first light-shielding material 12a and the second light-shielding material 12b is a resin composition that is colored to block light. In this embodiment, the first light-shielding material 12a and the second light-shielding material 12b are light-shielding tapes made of vinyl. The first light-shielding material 12a and the second light-shielding material 12b may be made of different materials. The second light-shielding material 12b may not exist, and the first light-shielding material 12a may entirely encase and cover the OSL element 16 and the photodetector 18.

[0020] The output signal of the photodetector 18 is input to the processor 8. From the output signal of the photodetector 18, the processor 8 counts the amount of radiation 20 incident on the photodetector 18 during a predetermined period. From the output signal of the photodetector 18, the processor 8 can calculate the amount of incident radiation, the amount of change in the radiation 20, etc. The processor 8 is realized, for example, by an AD converter that converts the output signal of the photodetector 18 into a digital signal and a microcontroller that processes the converted signal. The processor 8 may also be realized by a dedicated circuit. The result of the processor 8 is sent to the output device 10.

[0021] The output device 10 outputs the results of the processor 8. For example, the output device 10 displays the results of the processor 8 on a screen. The output device 10 may be provided with a storage device such as a hard disk, and may store the results of the processor 8. In this embodiment, the output device 10 is a personal computer. In this embodiment, the processor 8 and the output device 10 are realized separately, but the processor 8 and the output device 10 may also be integrated. The output device 10 may be configured to obtain the results of the processor 8 via a network.

[0022] The reader 11 reads the integrated radiation dose from the OSL element 16 of the radiation detector 2. The reader 11 shines light, for example from an LED, on the OSL element 16, causing the captured electrons and holes to recombine. The reader 11 detects the light emitted at this time and reads the integrated radiation dose. The reader 11 is the same as that used in conventional integrating dosimeters.

[0023] When using this dosimetry system 4, the user wears the radiation detector 2. The user undergoes, for example, a CT scan while wearing the radiation detector 2. At this time, radiation 20 incident on the radiation detector 2 causes the OSL element 16 to emit light, and this light is detected by the photodetector 18. The processor 8 processes the signal from the photodetector 18 to determine, for example, the dynamic radiation dose in real time. The result is displayed on the screen of the output device 10.

[0024] The user wears the same radiation detector 2 during examinations for a predetermined period of time. Even if the user undergoes multiple CT or X-ray examinations within the predetermined period of time, the user wears the same radiation detector 2 during the examinations. After the predetermined period has elapsed, the reader 11 measures the cumulative radiation dose received by the OSL element 16 of the radiation detector 2.

[0025] The effects of the radiation detector 2 will be described below.

[0026] As described above, in this radiation detector 2, the photodetector 18 detects the light emitted from the OSL element 16 when radiation 20 is incident on the OSL element 16. From this detection result, a dynamic radiation dose can be measured. In addition, this radiation detector 2 can measure the integrated radiation dose from the OSL element 16. Because this radiation detector 2 can measure the dynamic radiation dose in real time in addition to the integrated radiation dose, it is possible to improve the accuracy of measuring the exposure dose.

[0027] In this radiation detector 2, the OSL element 16 is used for both cumulative radiation dose measurement and dynamic radiation dose measurement, making it possible to make it smaller than conventional detectors. This radiation detector 2 has little impact on the examination. This radiation detector 2 makes it possible to measure cumulative radiation dose and dynamic radiation dose while minimizing the impact on the examination.

[0028] The radiation detector 2 has a structure in which an OSL element 16 and a photodetector 18 are stacked. When radiation 20 is incident on the OSL element 16, the light emitted by the OSL element 16 is weak. By stacking the OSL element 16 and the photodetector 18, the photodetector 18 can efficiently detect the light from the OSL element 16. From this perspective, it is preferable that the OSL element 16 and the photodetector 18 are in contact with each other.

[0029] In this radiation detector 2, first light-shielding material 12a and second light-shielding material 12b cover OSL element 16 and photodetector 18. If external light enters photodetector 18, it may not be possible to correctly detect the light from OSL element 16. By covering OSL element 16 and photodetector 18 with light-shielding material 12a, the light from OSL element 16 can be detected with high accuracy.

[0030] In this radiation detector 2, a reflector 14 is provided between the light-shielding material 12 and the OSL element 16. The reflector 14 reflects the light from the OSL element 16 and returns it to the photodetector 18, allowing the photodetector 18 to efficiently detect the light from the OSL element 16. From this perspective, it is preferable to have a reflector 14 also between the light-shielding material 12 and the photodetector 18. [Example]

[0031] The effects of the present radiation detector will be clarified below by way of examples, but the present invention should not be construed as being limited based on the descriptions of these examples.

[0032] [Experiment 1] [Example 1] The dose measurement system shown in Figures 1 and 2 was prepared. The radiation detector of this system was connected to an X-ray irradiation device (RADspeed Pro manufactured by Shimadzu Corporation). TM The specimen was irradiated with X-rays from the first light-shielding material side using a SR5 Version. The irradiation conditions were as follows: Tube voltage: 80kV Tube current: 80mA X-ray focus-detector distance (SDD): 100cm X-ray exposure time: 5 settings: 0.05 s, 0.1 s, 0.5 s, 1 s, 5 s For each of the above irradiation times, the number of times the OSL element emitted light detected by the photodetector (the number of electrons bonded with holes in the OSL element, which is proportional to the dynamic radiation dose) was counted by the processing unit. The results for the five irradiation times are shown in Figure 3. In Figure 3, symbol A on the horizontal axis represents the results for an irradiation time of 0.05 s (seconds), symbol B represents the results for an irradiation time of 0.1 s, symbol C represents the results for an irradiation time of 0.5 s, symbol D represents the results for an irradiation time of 1 s, and symbol E represents the results for an irradiation time of 5 s. The vertical axis represents the number of counts. In Figure 3, each "dot" represents one of the count measurements over a 10 ms period. For each irradiation time, the count is zero before irradiation and increases once irradiation begins. For example, for an irradiation time of 0.05 s (symbol A), the peak count over 10 ms is approximately 1,300. For example, in the case of an exposure time of 5 seconds (symbol E), the peak count within 10 ms is approximately 1600, and the number of "dots" is greater than with other exposure times. It can be seen that the longer the exposure time, the greater the number of counts as a detection result. In other words, the number of counts increases in proportion to the radiation dose.

[0033] [Example 2-3] The counts were measured in the same manner as in Example 1, except that the tube voltage of the X-ray irradiator was set to 40 kV and 120 kV. The respective results are shown in Figures 4(a) and 4(b). As can be seen from Figures 4(a) and 4(b) and Figure 3, the higher the tube voltage, the higher the counts as a detection result. In other words, the counts increase in proportion to the exposure dose.

[0034] [Experiment 2] [Example 4] The radiation detector in Figure 2 was placed on the imaging table of a CT scanner (TSX-035A Aquilion Lightning, manufactured by Canon Medical Systems, Inc.), and imaging was performed. The resulting image is shown in Figure 5(a). In Figure 5(a), the white object pointed to by the arrow number 2 at the top is the radiation detector. As can be seen from this figure, there are almost no artifacts caused by the radiation detector in the CT image. Even with the radiation detector, a correct CT image is obtained.

[0035] [Comparative Example 1] CT imaging was performed in the same manner as in Example 4, except that a commercially available semiconductor dosimeter was used as the radiation detector. The resulting image is shown in Figure 5(b). In Figure 5(b), the white object indicated by the arrow at the top, reference numeral 30, is the radiation detector. Compared to Figure 5(a), it can be seen that a large artifact has occurred at the bottom of the radiation detector.

[0036] As shown in Examples 1-3, this radiation detector obtains a count number proportional to the dynamic radiation dose. This radiation detector is capable of measuring dynamic radiation dose. Because this radiation detector has an OSL element, it is capable of measuring cumulative radiation dose as in the past. Furthermore, as can be seen from Example 4 and Comparative Example 1, this radiation detector reduces the impact on CT images. These facts clearly demonstrate the superiority of this embodiment.

[0037] [Disclosure items] The following items are disclosures of preferred embodiments.

[0038] [Item 1] a photostimulated luminescence element; a photodetector that detects light emitted from the photostimulated luminescence element when radiation is incident on the photostimulated luminescence element; A radiation detector comprising:

[0039] [Item 2] Item 2. The radiation detector according to item 1, wherein the photostimulated luminescence element and the photodetector are stacked.

[0040] [Item 3] 3. The radiation detector according to item 1 or 2, further comprising a light-shielding material covering the photostimulated luminescence element and the photodetector.

[0041] [Item 4] 4. The radiation detector according to any one of items 1 to 3, wherein the photodetector is a multi-pixel photon counter.

[0042] [Item 5] A radiation detector according to any one of items 1 to 4; a processor that calculates the radiation dose in real time from the output from the photodetector; a reader for reading the accumulated amount of radiation received by the optically stimulated luminescence element; A radiation dosimetry system comprising: [Industrial Applicability]

[0043] The radiation detectors described above are used to detect various types of radiation. [Explanation of symbols]

[0044] 2. Radiation detector 4. Dosimetry System 6...Power supply 8. Processor 10. Output device 11. Output device 12a...First light shielding material 12b...Second light shielding material 14...Reflective material 16···Photostimulated luminescence element (OSL element) 18. Photodetector 20. Radiation 22...first electrode 24...Second electrode

Claims

1. a photostimulated luminescence element; a photodetector that detects light emitted from the photostimulated luminescence element when radiation is incident on the photostimulated luminescence element; A radiation detector comprising:

2. The radiation detector of claim 1 , wherein the photostimulated luminescence element and the photodetector are stacked.

3. The radiation detector according to claim 1 , further comprising a light-shielding material covering the photostimulated luminescence element and the photodetector.

4. 3. The radiation detector of claim 1, wherein the photodetector is a multi-pixel photon counter.

5. The radiation detector according to claim 1 or 2; a processor that calculates the radiation dose in real time from the output from the photodetector; a reader for reading the accumulated amount of radiation received by the optically stimulated luminescence element; A radiation dosimetry system comprising:

Images