A method for boron neutron capture therapy beam gamma dose measurement

Abstract

The application discloses a kind of boron neutron capture therapy beam gamma dose measurement methods, it is related to radiotherapy technical field, first thermoluminescence dosimeter is standardized annealing pretreatment, and screening, numbering;Positioning and calibration are carried out to water equivalent phantom fixed on treatment bed, complete reference positioning;Thermoluminescence dosimeter is loaded in water equivalent phantom and is irradiated again;After irradiation, take out phantom, establish the one-to-one correspondence between unique number and its three-dimensional space position in phantom, and record;First measurement and second measurement are carried out to all dosimeters in turn, calculate thermoluminescence net gamma count, obtain absorbed dose value;Thermoluminescence dosimeter is annealed again, for subsequent circulation use conveniently.The application in the application multiple thermoluminescence dosimeters are irradiated simultaneously, shorten time;Two independent measurements, deduct interference signal;Complex operation process standardization, programming, improve measurement repeatability and efficiency, convenient, novel, accurate.

Description

Technical Field

[0001] This invention relates to the field of radiotherapy technology, and in particular to a method for measuring gamma dose in a boron neutron capture therapy beam. Background Technology

[0002] In boron neutron capture therapy (BNCT), gamma dose distribution is an important consideration. Current measurements have the following problems:

[0003] (1) Ionization chamber: It has a large volume, making it difficult to distinguish photons. The gas flow operation process is cumbersome and not conducive to rapid and efficient multiple measurements.

[0004] (2) Semiconductor detectors: require specific neutron shielding or correction, and are costly.

[0005] (3) Film dosimeter: has limited ability to distinguish photons, cannot be reused, and requires recalibration for different batches.

[0006] Therefore, there is an urgent need to develop a method for measuring gamma dose in boron neutron capture therapy beams that can achieve rapid, accurate, low-error, and highly repeatable measurements. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention discloses a method for measuring gamma dose in boron neutron capture therapy beams. This method involves simultaneous irradiation with multiple thermoluminescent dosimeters, shortening the time required; employing two independent measurements to eliminate interference signals caused by nuclide decay, etc.; and standardizing and proceduralizing complex operating procedures to improve measurement repeatability and efficiency.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The steps include:

[0010] (1) Standardized annealing pretreatment was performed on thermoluminescent dosimeters from the same batch;

[0011] (2) The pretreated thermoluminescent dosimeters were screened for sensitivity consistency and given unique numbers;

[0012] (3) Install and fix the water equivalent phantom on the treatment bed, and use the three-dimensional laser positioning system and treatment bed control system in the treatment room to position and calibrate the phantom, adjust the position of the treatment bed and the water equivalent phantom, and complete the reference positioning of the water equivalent phantom;

[0013] (4) Load the thermoluminescent dosing strip into the placement slot of the water equivalent phantom, complete the loading of the thermoluminescent dosing strip and the assembly of the phantom, then move the treatment bed to a predetermined safe position away from the treatment head outlet, then fix the assembled phantom in the designated position of the treatment bed, operate the treatment bed control system, and precisely move and position the treatment bed to the reference positioning coordinate position for irradiation.

[0014] (5) After irradiation, continuously monitor the radiation level in the treatment room. When it drops to the dose rate management limit of the radiation control area in the national standard, personnel wearing personal dosimeters enter the treatment room, quickly remove the phantom, and take the thermoluminescent dosimeter from the phantom placement slot. Simultaneously establish a one-to-one correspondence between the unique number and its three-dimensional spatial position in the phantom and record it. Immediately place the removed thermoluminescent dosimeter in a lead container for transportation and storage.

[0015] (6) Using a standard annealed and unirradiated dose sheet, perform a complete standard heating procedure, measure and record the integrated signal value read out as the system background reference value including material background, environmental cumulative dose and electronic noise. Then, take the thermoluminescent dose sheet out of the lead container and place it at the geometric center of the heating plate of the thermoluminescent reader. Using the thermoluminescent reader, call and execute the defined standard heating readout procedure corresponding to the dose response calibration coefficient of this batch of dose sheets, measure and record the integrated signal value released during the heating process, and automatically stop the measurement after the heating procedure is completed. Complete the first measurement of all dose sheets in the order of their unique numbers.

[0016] (7) Place the thermoluminescent dosimeters that have been measured back into the lead container and store them for cooling for at least 24 hours. Then, place the cooled thermoluminescent dosimeters back into the thermoluminescent reader according to their unique numbers and heat them again to complete the second measurement.

[0017] (8) Calculate the net gamma count of thermoluminescence The absorbed dose value of the thermoluminescent dosimeter in the AB-BNCT radiation field was obtained. ;

[0018] (9) After all measurements and data recordings are completed, all thermoluminescent dosimeters are annealed again according to the same standard annealing procedure defined in the initial pretreatment of this batch of dosimeters to eliminate residual signals and restore them to the zero dose value reference state for subsequent recycling.

[0019] Furthermore, in step (1), the thermoluminescent dosimeter is TLD-400, manufactured from a single production batch, and the proportions of the main material and dopants are clearly defined, without the addition of other impurities;

[0020] Preprocessing:

[0021] The thermoluminescent dosimeter was placed in an annealing furnace with a set standard annealing temperature and thermal equilibrium. The temperature was maintained at that temperature for a standard annealing time, so that the thermoluminescent signal of the thermoluminescent dosimeter was attenuated to the background level.

[0022] After completion, the thermoluminescent dosimeter tablets are removed from the annealing furnace and allowed to cool naturally to room temperature in a dry, dust-free environment to unify their initial state.

[0023] Furthermore, the specific process of step (2) is as follows:

[0024] 21) The pretreated thermoluminescent dosimeters were placed in a gamma radiation field with uniform irradiation field calibrated by a standard laboratory. Under the preset fixed irradiation conditions, all thermoluminescent dosimeters were subjected to single, synchronous irradiation to ensure that the absorbed dose was the same.

[0025] 22) Using a calibrated thermoluminescent reader, read and record the total integrated signal count for all thermoluminescent dosimeters;

[0026] 23) Based on the counting results, calculate the average response value of the batch of dose tablets, and screen out thermoluminescent dose tablets whose counts deviate from the average value by ±5%.

[0027] 24) Each selected thermoluminescent dosimeter is uniquely numbered, and a record is established containing the number and the total count of the corresponding integrated signal. At the same time, the measurement personnel, the start time of measurement, the heating rate, the total measurement time, the highest heating temperature, and the high voltage value of the photomultiplier tube of the reader are recorded.

[0028] Further, in step (3), the water equivalent phantom is a cube or cuboid with a size of not less than 30cm×30cm×30cm, and the phantom is pre-processed with a placement groove for accommodating thermoluminescent dosing sheets.

[0029] By adjusting the positions of the treatment bed and the water equivalent phantom, the incident surface of the water equivalent phantom is aligned with the collimation plane of the treatment head beam, ensuring that the geometric central axis of the water equivalent phantom coincides with the central axis of the treatment beam in three-dimensional space.

[0030] Furthermore, in step (4), during the irradiation process, a proton flux monitoring system based on the accelerator boron neutron capture therapy system is simultaneously activated to monitor the proton flux incident on the target in real time and record the experimental date, operator, irradiation time, start time of irradiation, stop time of irradiation, and proton flux.

[0031] Furthermore, during the first measurement in step (6) and the second measurement in step (7), the recorded data includes: the operator for each measurement, the measurement start time, the total measurement time, the heating rate, the maximum heating temperature, the luminescence curve, the unique number, the location number of the phantom, the high voltage value of the photomultiplier tube of the reader, and the total count of the integral signal.

[0032] Furthermore, in step (8), the formula for calculating the net gamma count of thermoluminescence is:

[0033] ;

[0034] In the formula, This is the net thermoluminescence count signal obtained from the first measurement. This is the net thermoluminescence counting signal obtained from the second measurement. is the radiative decay constant of the doped material in the thermoluminescent material. Irradiation time, Cooling time;

[0035] Absorbed dose value of thermoluminescent dosimeter in AB-BNCT radiation field The calculation formula is:

[0036] ;

[0037] In the formula, This is the absorbed dose value. For calibration factor, The net gamma count for thermoluminescence.

[0038] The beneficial effects of this invention are that, compared with the prior art, this method has the following advantages:

[0039] (1) Multiple thermoluminescent dosing plates can be irradiated simultaneously, requiring only one irradiation, which greatly reduces the measurement time of the experiment.

[0040] (2) Through standardized annealing pretreatment, the background signal and historical residue of the dosing tablets were effectively eliminated, ensuring the purity and consistency of the measurement starting point.

[0041] (3) By using two independent measurements, interference signals caused by nuclide decay and other factors can be effectively deducted.

[0042] (4) By using unique numbers to associate the location of the dose tablets, measurement data and process parameters, data traceability and cross-verification can be achieved, thereby ensuring the reliability and accuracy of the spatial distribution measurement results of gamma dose.

[0043] (5) By standardizing material batches, precision machining of models and coordinate positioning, systematic errors in materials, geometry and operation are effectively reduced.

[0044] (6) Standardizing and proceduralizing complex operating procedures significantly improves the repeatability and efficiency of experiments.

[0045] (7) The measurement process is simple and convenient. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the monitoring system in an embodiment of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] This invention discloses a method for measuring gamma dose in a boron neutron capture therapy beam, specifically including the following steps:

[0049] (1) Prepare thermoluminescent dosing tablets and water equivalent phantoms.

[0050] The thermoluminescent dosimeter is TLD-400, manufactured in a single production batch. The proportions of the main material and dopants must be clearly defined, and no other impurities may be added.

[0051] The equivalent phantom is a cube or cuboid with dimensions not less than 30 cm × 30 cm × 30 cm. The material must not contain any non-equivalent material that would impair the water equivalence. Furthermore, the phantom must be pre-machined with a placement groove for accommodating the thermoluminescent sheet, and the dimensions of the placement groove must match the physical dimensions of the thermoluminescent sheet.

[0052] (2) Perform standardized annealing pretreatment on the same batch of thermoluminescent dosimeters.

[0053] The dose tablets are placed in an annealing furnace set at the standard annealing temperature and in a state of thermal equilibrium (the temperature uniformity of the annealing furnace in the effective working area is better than ±2℃, and the temperature control accuracy is better than ±1℃). The temperature is maintained at this temperature for a certain period of time, which is sufficient for the thermoluminescence signal of the dose tablets to decay to the background level.

[0054] After the isothermal maintenance is completed, the tablets are removed from the annealing furnace and allowed to cool naturally to room temperature (20-25°C) in a dry, dust-free environment to unify their initial state.

[0055] (3) Screen the pretreated thermoluminescent dosimeters and assign them unique numbers.

[0056] Thermoluminescent dosimeters were placed in a gamma radiation field calibrated in a standard laboratory with a field uniformity better than ±2%. Under preset fixed irradiation conditions, all dosimeters were subjected to single, synchronous irradiation to ensure that they received the same absorbed dose.

[0057] Subsequently, using a calibrated thermoluminescent reader, and setting a procedure and parameters that are completely consistent with the defined standard heating readout procedure used when calibrating the dose response of this batch of thermoluminescent dosimeters, including the same heating rate, maximum temperature and holding time, the total count of the integrated signal of all dosimeters was read and recorded sequentially.

[0058] Based on the counting results, the average response value of the batch of dose tablets is calculated, and thermoluminescent dose tablets with a deviation of the count from the average value within ±5% are selected.

[0059] Finally, each selected thermoluminescent dosimeter is uniquely numbered, and a total count record containing the number and corresponding integral signal is established. At the same time, the measurement personnel, the start time of measurement, the heating rate, the total measurement time, the highest heating temperature, and the high voltage value of the photomultiplier tube of the reader are also recorded.

[0060] (4) Perform the experimental pre-positioning operation.

[0061] The water equivalent phantom is installed and fixed on the treatment bed. Based on the positioning marks machined on the surface of the phantom and having a defined geometric relationship with the internal placement groove, the phantom is positioned and calibrated with the help of a three-dimensional laser positioning system and a treatment bed control system in the treatment room.

[0062] By adjusting the positions of the treatment bed and the phantom, the incident surface of the phantom is aligned with the collimation plane of the treatment head beam, and the geometric center axis of the phantom coincides with the center axis of the treatment beam in three-dimensional space. This state is defined as the "reference position" for this dose measurement. The information required for this reference position is recorded and saved, including the fixed position information of the phantom on the treatment bed, and the coordinate values ​​of each axis displayed by the treatment bed control system.

[0063] (5) Complete the loading and assembly of the thermoluminescent dose-equivalent phantom, irradiate and monitor it.

[0064] The selected and numbered thermoluminescent dosimeters are sequentially placed into the placement tank of the pre-processed water equivalent phantom, completing the loading of the thermoluminescent dosimeters and the assembly of the phantom. Then, the treatment bed is moved to a predetermined safe position away from the treatment head's beam exit, and the assembled phantom is fixed in the designated position on the treatment bed, its position consistent with the "reference position" record. Next, the treatment bed control system is operated to precisely move and position the treatment bed to the "reference position" coordinates recorded and saved in the previous steps, followed by irradiation. During irradiation, the proton flux monitoring system based on the accelerator boron neutron capture therapy (AB-BNCT) system is simultaneously activated, such as... Figure 1 As shown, the proton flux incident on the target was monitored in real time. During this process, the experiment date, operator, irradiation time, start time of irradiation, stop time of irradiation, and proton flux were recorded.

[0065] (6) Take out the thermoluminescent dosing tablet and record it.

[0066] After irradiation, the radiation level in the treatment room is continuously monitored. When it drops to the national standard radiation control zone dose rate management limit (usually 2.5 μSv / h), personnel wearing personal dosimeters enter the treatment room and quickly remove the phantom. The thermoluminescent dosimeter is removed from the phantom placement slot. When removing each dosimeter, a unique number is simultaneously established and recorded in relation to its three-dimensional spatial position in the phantom. Subsequently, the removed dosimeter is immediately placed in a lead container for transport and storage.

[0067] (7) Complete the first measurement.

[0068] Without a sample, perform a complete standard heating procedure, measure and record the integrated signal value read out, and use it as a reference value for the system's electronic background and thermal noise.

[0069] The thermoluminescent dosimeter tablets are then removed from the lead container and placed at the geometric center of the heating plate of the thermoluminescent reader. Using the thermoluminescent reader, the defined standard heating readout program corresponding to the dose response calibration coefficient of this batch of dosimeter tablets is invoked and executed, and the integral signal released during the heating process is measured. The measurement is automatically stopped after the heating program is completed.

[0070] The measurements of all dose tablets were performed sequentially according to their unique serial numbers. During this process, the operator, start time, total measurement time, heating rate, maximum heating temperature, emission curve, unique serial number, location number of the phantom, photomultiplier tube high voltage value, and total integral signal count were recorded for each measurement. This measurement was the first measurement.

[0071] (8) The thermoluminescent dosimeter is stored and cooled.

[0072] After the thermoluminescent dosimeters have been measured, they are placed back into lead containers and stored and cooled under controlled environmental conditions for at least 24 hours.

[0073] (9) Complete the second measurement.

[0074] After cooling, the thermoluminescent dosimeter tablets, based on their unique serial numbers, are placed back into the thermoluminescent reader and reheated using the same standard heating and readout procedure and parameters used for dose response calibration of this batch of thermoluminescent dosimeter tablets. During this process, the operator, start time, total measurement time, heating rate, maximum heating temperature, emission curve, unique serial number, location number of the phantom, photomultiplier tube high voltage value of the reader, and total integral signal count are recorded for each measurement. This measurement is the second measurement.

[0075] (10) Calculate the net gamma count and absorbed dose value of thermoluminescence.

[0076] Formula for calculating the net gamma count of thermoluminescence:

[0077] (1);

[0078] in: The net thermoluminescence count signal obtained from the first measurement (after deducting the system background). The net thermoluminescence counting signal obtained from the second measurement (after deducting the system background). is the radiative decay constant of the doped material (such as Mn) in thermoluminescent materials. Irradiation time; This refers to the cooling time.

[0079] The calculated net thermoluminescent gamma count is compared with a calibration factor obtained beforehand using a standard gamma field with a traceable calibration factor to calculate the absorbed dose value of the thermoluminescent dosimeter in the AB-BNCT radiation field, as shown in the following formula:

[0080] (2);

[0081] in: For absorbed dose, For calibration factor, The net gamma count for thermoluminescence.

[0082] (11) Annealing was performed on all thermoluminescent dosimeters.

[0083] After all measurements and data recordings were completed, all thermoluminescent dosimeters were annealed again according to the same standard annealing procedure (including temperature, time and cooling conditions) defined for the initial pretreatment of this batch of dosimeters. This was done to completely eliminate any residual thermoluminescent signals from this experiment and restore them to a uniform low-background initial state for subsequent recycling.

[0084] This invention utilizes the TLD-400 thermoluminescence method to measure the gamma dose of a boron neutron capture therapy beam. The measurement process is convenient, fast, novel, and accurate.

[0085] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for measuring gamma dose in a boron neutron capture therapy beam, characterized in that the steps include... include: (1) Standardized annealing pretreatment was performed on thermoluminescent dosimeters from the same batch; (2) The pretreated thermoluminescent dosimeters were screened for sensitivity consistency and uniquely numbered; (3) Install and fix the water equivalent phantom on the treatment bed, and use the three-dimensional laser positioning system and treatment bed control system in the treatment room to position and calibrate the phantom, adjust the position of the treatment bed and the water equivalent phantom, and complete the reference positioning of the water equivalent phantom; (4) Load the thermoluminescent dosing strip into the placement slot of the water equivalent phantom, complete the loading of the thermoluminescent dosing strip and the assembly of the phantom, then move the treatment bed to a predetermined safe position away from the treatment head outlet, then fix the assembled phantom in the designated position of the treatment bed, operate the treatment bed control system, and precisely move and position the treatment bed to the reference positioning coordinate position for irradiation. (5) After irradiation, continuously monitor the radiation level in the treatment room. When it drops to the dose rate management limit of the radiation control area in the national standard, personnel wearing personal dosimeters enter the treatment room, quickly remove the phantom, and take the thermoluminescent dosimeter from the phantom placement slot. Simultaneously establish a one-to-one correspondence between the unique number and its three-dimensional spatial position in the phantom and record it. Immediately place the removed thermoluminescent dosimeter in a lead container for transportation and storage. (6) Using a standard annealed and unirradiated dose sheet, perform a complete standard heating procedure, measure and record the integrated signal value read out as the system background reference value including material background, environmental cumulative dose and electronic noise. Then, take the thermoluminescent dose sheet out of the lead container and place it at the geometric center of the heating plate of the thermoluminescent reader. Using the thermoluminescent reader, call and execute the defined standard heating readout procedure corresponding to the dose response calibration coefficient of this batch of dose sheets, measure and record the integrated signal value released during the heating process, and automatically stop the measurement after the heating procedure is completed. Complete the first measurement of all dose sheets in the order of their unique numbers. (7) Place the thermoluminescent dosimeters that have been measured back into the lead container and store them for cooling for at least 24 hours. Then, place the cooled thermoluminescent dosimeters back into the thermoluminescent reader according to their unique numbers and heat them again to complete the second measurement. (8) Calculate the net gamma count of thermoluminescence The absorbed dose value of the thermoluminescent dosimeter in the AB-BNCT radiation field was obtained. ; (9) After all measurements and data recordings are completed, all thermoluminescent dosimeters are annealed again according to the same standard annealing procedure defined in the initial pretreatment of this batch of dosimeters to eliminate residual signals and restore them to the zero dose value reference state for subsequent recycling.

2. The method for measuring gamma dose in a boron neutron capture therapy beam according to claim 1, characterized in that, In step (1), the thermoluminescent dosimeter is made of TLD-400, produced from a single batch, and the proportions of the main material and dopants are clearly defined, without any other impurities added. Preprocessing: The thermoluminescent dosimeter was placed in an annealing furnace with a set standard annealing temperature and thermal equilibrium. The temperature was maintained at that temperature for a standard annealing time, so that the thermoluminescent signal of the thermoluminescent dosimeter was attenuated to the background level. After completion, the thermoluminescent dosimeter tablets are removed from the annealing furnace and allowed to cool naturally to room temperature in a dry, dust-free environment to unify their initial state.

3. The method for measuring gamma dose in a boron neutron capture therapy beam according to claim 1, characterized in that, The specific process of step (2): 21) The pretreated thermoluminescent dosimeters were placed in a gamma radiation field with uniform irradiation field calibrated by a standard laboratory. Under the preset fixed irradiation conditions, all thermoluminescent dosimeters were subjected to single, synchronous irradiation to ensure that the absorbed dose was the same. 22) Using a calibrated thermoluminescent reader, read and record the total integrated signal count for all thermoluminescent dosimeters; 23) Based on the counting results, calculate the average response value of the batch of dose tablets, and screen out thermoluminescent dose tablets whose counts deviate from the average value by ±5%. 24) Each selected thermoluminescent dosimeter is uniquely numbered, and a record is established containing the number and the total count of the corresponding integrated signal. At the same time, the measurement personnel, the start time of measurement, the heating rate, the total measurement time, the highest heating temperature, and the high voltage value of the photomultiplier tube of the reader are recorded.

4. The method for measuring gamma dose in a boron neutron capture therapy beam according to claim 1, characterized in that, In step (3), the water equivalent phantom is a cube or cuboid with a size of not less than 30cm×30cm×30cm, and the phantom is pre-processed with a placement groove for accommodating thermoluminescent dosing sheets. By adjusting the positions of the treatment bed and the water equivalent phantom, the incident surface of the water equivalent phantom is aligned with the collimation plane of the treatment head beam, ensuring that the geometric central axis of the water equivalent phantom coincides with the central axis of the treatment beam in three-dimensional space.

5. The method for measuring gamma dose in a boron neutron capture therapy beam according to claim 1, characterized in that, In step (4), during the irradiation process, the proton flux monitoring system based on the accelerator boron neutron capture therapy system is activated simultaneously to monitor the proton flux incident on the target in real time and record the experimental date, operator, irradiation time, start time of irradiation, stop time of irradiation, and proton flux.

6. The method for measuring gamma dose in a boron neutron capture therapy beam according to claim 1, characterized in that, During the first measurement in step (6) and the second measurement in step (7), the recorded data includes: the operator of each measurement, the measurement start time, the total measurement time, the heating rate, the maximum heating temperature, the light emission curve, the unique number, the location number of the phantom, the high voltage value of the photomultiplier tube of the reader, and the total count of the integral signal.

7. The method for measuring gamma dose in a boron neutron capture therapy beam according to claim 1, characterized in that, In step (8), the formula for calculating the net gamma count of thermoluminescence is: ； In the formula, This is the net thermoluminescence count signal obtained from the first measurement. This is the net thermoluminescence counting signal obtained from the second measurement. is the radiative decay constant of the doped material in the thermoluminescent material. Irradiation time, Cooling time; Absorbed dose value of thermoluminescent dosimeter in AB-BNCT radiation field The calculation formula is: ； In the formula, This is the absorbed dose value. For calibration factor, The net gamma count for thermoluminescence.

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