Method for measuring epithermal neutrons of boron neutron capture therapy beam

Abstract

The invention discloses a method for measuring epithermal neutrons of a boron neutron capture therapy beam, and relates to the field of neutron measurement, and the method comprises the steps: carrying out the positioning of a neutron detector, enabling the front end of the neutron detector to be aligned with the plane of a beam outlet of a boron neutron capture therapy head, the beam central axis of the boron neutron capture treatment head coincides with the central axis of the neutron detector; placing an activation foil in the neutron detector to obtain an assembled neutron detector; placing the assembled neutron detector at a specified position on a treatment bed, then moving the treatment bed to the specified position, and performing irradiation; taking out the activated foil after the irradiation is finished; an induced radioactivity measurement is performed on the activated foil to determine the epithermal neutron flux. According to the invention, the measurement process of the epithermal neutrons is simplified, the measurement efficiency is improved, and the measurement time is saved.

Description

Technical Field

[0001] The present application relates to the field of neutron measurement, and in particular to a method for measuring epithermal neutrons in a boron neutron capture therapy beam. Background Art

[0002] Before conducting boron neutron capture therapy (BNCT), it is necessary to measure the epithermal neutron flux. The current measurement methods include the gold foil activation method and the multi-foil energy spectrum inversion method. Both rely on Monte Carlo simulation. The gold foil activation method uses cadmium-coated gold foil for measurement, which is cumbersome and time-consuming. The multi-foil energy spectrum inversion method infers the epithermal neutron flux through the measured energy spectrum, and the measurement accuracy is low. Summary of the invention

[0003] The purpose of the present application is to provide a method for measuring epithermal neutrons in a boron neutron capture therapy beam, which can improve measurement accuracy, simplify the measurement process of epithermal neutron flux, save measurement time, and realize daily quality detection of the boron neutron capture therapy beam.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides a method for measuring epithermal neutrons in a boron neutron capture therapy beam, comprising:

[0006] Positioning the neutron detector so that the front end of the neutron detector is aligned with the beam outlet plane of the boron neutron capture therapy head, and the beam center axis of the boron neutron capture therapy head coincides with the center axis of the neutron detector;

[0007] placing an activated foil in the neutron detector to obtain an assembled neutron detector;

[0008] placing the assembled neutron detector at a designated position on the treatment bed, then moving the treatment bed to a designated position in the treatment room, and performing irradiation;

[0009] After the irradiation is finished, remove the activated foil;

[0010] The activated foils were subjected to induced radioactivity measurements to determine the epithermal neutron flux.

[0011] Optionally, the surface of the neutron detector has a positioning mark; positioning the neutron detector specifically includes: positioning the neutron detector according to the positioning mark on the surface of the neutron detector, a treatment room laser positioning system, and a treatment bed control system.

[0012] Optionally, placing the assembled neutron detector at a designated position on the treatment bed, and then moving the treatment bed to the designated position, specifically includes: placing the assembled neutron detector at a designated position on the treatment bed, and moving the treatment bed to the designated position in the treatment room using the treatment bed control system.

[0013] Optionally, removing the activated foil after the irradiation is completed specifically includes: after the irradiation is completed and the dose level in the treatment room drops to a range that allows operation, removing the assembled neutron detector from the treatment room and removing the activated foil from the neutron detector; placing the activated foil in a lead tank for transportation and cooling.

[0014] Optionally, the activated foil is subjected to induced radioactivity measurement to determine the epithermal neutron flux, specifically comprising: using a high-purity germanium gamma spectrometer to measure the peak count of characteristic gamma rays emitted when the activated foil decays; calculating the reaction rate of the activated foil according to the peak count of the characteristic gamma rays, the irradiation time of the activated foil, the cooling time of the activated foil and the measurement time of the characteristic gamma rays; and calculating the epithermal neutron flux according to the reaction rate of the activated foil.

[0015] Optionally, the reaction rate of the activated foil is calculated using the following formula:

[0016]

[0017] Where RR is the reaction rate of the activated foil (in s -1 ), N is the peak count of characteristic gamma rays, λ is the decay constant of the radionuclide in the activated foil (in s -1 ), f c is the cascade coincidence correction factor of the characteristic gamma ray, f s is the self-absorption correction coefficient of the activated foil, ε is the detection efficiency of the high-purity germanium gamma spectrometer for characteristic gamma rays, I γ is the branching ratio of characteristic gamma rays, f g is the geometric factor correction coefficient, t a is the irradiation time of the activated foil (in seconds), t c is the cooling time of the activated foil (in seconds), t m is the measurement time of characteristic gamma rays (in seconds), n is the number of segments of irradiation time, I i is the average proton beam intensity of the irradiation time in the i-th period (in mA), is the average proton beam intensity during the entire irradiation process (in mA).

[0018] Optionally, the epithermal neutron flux is calculated using the following formula:

[0019]

[0020] Among them, φ epi is the epithermal neutron flux (in n cm -2 s -1 ), η is the response of the neutron detector (in cps (n cm -2 s -1 ) -1 atoms -1 ), N a is the number of target nuclei in the activated foil (in atoms).

[0021] According to the specific embodiments provided in this application, this application has the following technical effects:

[0022] The present application provides a method for measuring epithermal neutrons in a boron neutron capture therapy beam, which comprises positioning a neutron detector, placing an activated foil in the neutron detector, placing the assembled neutron detector in a designated position in a treatment room, performing irradiation, taking out the activated foil after the irradiation, and measuring the induced radioactivity of the activated foil to determine the epithermal neutron flux. The method simplifies the measurement process of the epithermal neutron flux, saves measurement time, has high measurement accuracy, and can directly measure the epithermal neutron flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic flow chart of a method for measuring epithermal neutrons in a boron neutron capture therapy beam provided in one embodiment of the present application. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0027] In an exemplary embodiment, Figure 1 As shown, a method for measuring epithermal neutrons in a boron neutron capture therapy beam is provided, comprising the following steps 101 to 105 .

[0028] Step 101, positioning the neutron detector so that the front end of the neutron detector is aligned with the beam outlet plane of the boron neutron capture therapy head, and the beam center axis of the boron neutron capture therapy head coincides with the center axis of the neutron detector.

[0029] In an exemplary embodiment, the activation material (activation foil) and the main body of the neutron detector are first prepared. The activation material requires that the isotope ratio of the main activation element is clear and no other activated nuclides are added. The main body requires a clear density, no other nuclides are added, a processing accuracy of 0.01mm, and the neutron incident surface is marked so that the surface of the neutron detector has positioning marks.

[0030] The neutron detector is positioned according to the positioning marks on the surface of the neutron detector, the laser positioning system of the treatment room and the control system of the treatment bed.

[0031] Step 101 is the preparation work before measurement, which is to first determine the position of the neutron detector and the coordinates of the treatment bed. In the subsequent step 103, the neutron detector and the treatment bed can be directly moved to the position determined in step 101.

[0032] Step 102, placing an activated foil in the neutron detector to obtain an assembled neutron detector.

[0033] In an exemplary embodiment, an electronic analytical balance is used to weigh the activated foil for calculating the number of target nuclei in the activated foil, wherein the accuracy of the electronic analytical balance is better than or equal to 0.1 mg.

[0034] Step 103, placing the assembled neutron detector at a designated position on the treatment bed, then moving the treatment bed to the designated position, and performing irradiation.

[0035] In an exemplary embodiment, the assembled neutron detector is placed at a designated position on the treatment bed, and the treatment bed control system is used to move the treatment bed to a designated position in the treatment room. Specifically, the treatment bed is moved to a position far from the beam outlet, the assembled neutron detector is placed on a detector bracket located at a designated position on the treatment bed, and the treatment bed is moved to the designated coordinates before irradiation.

[0036] Step 104, removing the activated foil after the irradiation is completed.

[0037] In an exemplary embodiment, after irradiation is completed and the dose level in the treatment room drops to a range that allows operation, the assembled neutron detector is taken out of the treatment room, and the activated foil is taken out of the assembled neutron detector, and the activated foil is placed in a lead tank for transportation and cooling.

[0038] Step 105 , performing induced radioactivity measurement on the activated foil to determine the epithermal neutron flux.

[0039] In an exemplary embodiment, the activated foil is first taken out of the lead tank and placed in the center of the sample holder, and the center of the activated foil and the sample holder is required to be located on the central axis of the detector of the high-purity germanium gamma spectrometer. Then, the peak count of the characteristic gamma rays emitted when the activated foil decays is measured by the high-purity germanium gamma spectrometer, and the measurement can be stopped when the peak count exceeds 10,000.

[0040] The reaction rate of the activated foil is calculated based on the peak count of the characteristic gamma ray, the irradiation time of the activated foil, the cooling time of the activated foil and the measurement time of the characteristic gamma ray:

[0041]

[0042] Where RR is the reaction rate of the activated foil (in s -1 ), N is the peak count of characteristic gamma rays, λ is the decay constant of the radionuclide in the activated foil (in s -1 ), f c is the cascade coincidence correction factor of the characteristic gamma ray, f s is the self-absorption correction coefficient of the activated foil, ε is the detection efficiency of the high-purity germanium gamma spectrometer for characteristic gamma rays, I γ is the branching ratio of characteristic gamma rays, f g is the geometric factor correction coefficient, t a is the irradiation time of the activated foil (in seconds), t c is the cooling time of the activated foil (in seconds), t m is the measurement time of characteristic gamma rays (in seconds), n is the number of segments of irradiation time, I i is the average proton beam intensity of the irradiation time in the i-th period (in mA), is the average proton beam intensity during the entire irradiation process (in mA).

[0043] The epithermal neutron flux is calculated based on the reactivity of the activated foil 201:

[0044]

[0045] Among them, φ epi is the epithermal neutron flux (in n cm -2 s -1 ), η is the response of the neutron detector (in cps (n cm -2 s -1 ) -1 atoms -1 ), N ais the number of target nuclei in the activated foil (in atoms).

[0046] The method for measuring epithermal neutrons in a boron neutron capture therapy beam provided in the present application has high measurement accuracy, simplifies the measurement process of epithermal neutron flux, has a simple and convenient measurement process, saves measurement time, and is suitable for daily quality detection of a boron neutron capture therapy beam.

[0047] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0048] In this application, all actions to obtain signals, information or data are carried out in compliance with the relevant data protection laws and policies of the country where they are located and with the authorization given by the owner of the corresponding device.

[0049] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for measuring epithermal neutrons in boron neutron capture therapy beams, characterized in that: The boron neutron capture therapy beam epithermal neutron measurement method comprises: Positioning the neutron detector so that the front end of the neutron detector is aligned with the beam outlet plane of the boron neutron capture therapy head, and the beam center axis of the boron neutron capture therapy head coincides with the center axis of the neutron detector; placing an activated foil in the neutron detector to obtain an assembled neutron detector; placing the assembled neutron detector at a designated position on the treatment bed, then moving the treatment bed to the designated position and performing irradiation; After the irradiation is finished, remove the activated foil; The activated foils were subjected to induced radioactivity measurements to determine the epithermal neutron flux.

2. The method for measuring epithermal neutrons in boron neutron capture therapy beam according to claim 1, characterized in that: The surface of the neutron detector has a positioning mark; positioning the neutron detector specifically includes: The neutron detector is positioned according to the positioning marks on the surface of the neutron detector, the laser positioning system of the treatment room and the control system of the treatment bed.

3. The method for measuring epithermal neutrons in boron neutron capture therapy beam according to claim 1, characterized in that: Placing the assembled neutron detector at a designated position on the treatment bed, and then moving the treatment bed to the designated position, specifically including: The assembled neutron detector is placed at a designated position on the treatment bed, and the treatment bed is moved to the designated position in the treatment room using the treatment bed control system.

4. The method for measuring epithermal neutrons in boron neutron capture therapy beam according to claim 1, characterized in that: Removing the activated foil after irradiation specifically involves: After the irradiation is completed and the dose level in the treatment room drops to a range within which the operation is allowed, the assembled neutron detector is taken out of the treatment room, and the activated foil is taken out from the neutron detector; The activated foil was placed in lead cans for transport and cooling.

5. The method for measuring epithermal neutrons in boron neutron capture therapy beam according to claim 1, characterized in that: The activated foil is subjected to induced radioactivity measurement to determine the epithermal neutron flux, specifically comprising: Using a high-purity germanium gamma spectrometer to measure the peak count of characteristic gamma rays emitted when the activated foil decays; Calculating the reaction rate of the activated foil according to the peak count of the characteristic gamma ray, the irradiation time of the activated foil, the cooling time of the activated foil and the measurement time of the characteristic gamma ray; The epithermal neutron flux is calculated from the reactivity of the activated foil.

6. The method for measuring epithermal neutrons in boron neutron capture therapy beam according to claim 5, characterized in that: The reaction rate of activated foil is calculated using the following formula: Where RR is the reaction rate of the activated foil, in seconds -1 , N is the peak count of characteristic gamma rays, λ is the decay constant of the radionuclide in the activated foil, in seconds -1 , f c is the cascade coincidence correction factor of the characteristic gamma ray, f s is the self-absorption correction coefficient of the activated foil, ε is the detection efficiency of the high-purity germanium gamma spectrometer for characteristic gamma rays, I γ is the branching ratio of characteristic gamma rays, f g is the geometric factor correction coefficient, t a is the irradiation time of the activated foil, in seconds, t c is the cooling time of the activated foil, in seconds, t m is the measurement time of characteristic gamma rays, in seconds, n is the number of segments of irradiation time, I i is the average proton beam intensity of the irradiation time in the i-th period, in mA, It is the average proton beam intensity during the entire irradiation process, in mA.

7. The method for measuring epithermal neutrons in boron neutron capture therapy beam according to claim 6, characterized in that: The epithermal neutron flux is calculated using the following formula: Among them, φ epi is the epithermal neutron flux, in n cm -2 s -1 , η is the response of the neutron detector, in cps (n cm -2 s -1 ) -1 atoms -1 , N a is the number of target nuclei in the activated foil, in atoms.

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