| With the rapid development of ionizing radiation technology,more and more fields have begun to pay more attention to the effective use of ionizing radiation.Currently in the medical field,radiation therapy has a very important position.Radiation therapy can use radiation to kill targets accurately and effectively,and it can be applied to almost all organs.The treatment process is also more convenient than surgical treatment,and it has less psychological impact on patients.However,considering that the radiation used during the treatment also damages the normal tissues of the human body,it is necessary to perform accurate calculation and measurement of the dose received by the human body.Because it is more difficult to measure the absorbed dose of the human body,the absorbed dose of water is usually measured to replace the absorbed dose of the human body.The high energy photon water absorbed dose was measured using the high energy photon water absorbed dose measurement method recommended by the International Atomic Energy Agency(IAEA)in the TRS398 report issued in 2000.In this paper,the water absorption dose measurement method for high-energy photons is analyzed.Based on the fact that the transmission of the water absorption dose calibration factor in China is not yet universal,the water absorption dose calibration factor is calculated by using the irradiation calibration factor.The method steps used are as follows:1?Use the 60 Co reference radiation field constructed by the storage tank,laser positioning device,aperture,moving rail and measuring platform,and verify the inverse square law of the reference radiation field built by the finger ionization chamber and the movable guide rail;The homogeneity of the reference radiation field was verified using a finger ionization chamber,a moving guide rail,and a measurement table;the ray scattering share of the region of interest was calculated using the Monte Carlo simulation method;and the leak ray around and at the top of the reservoir was finally measured.influences.2?The medical accelerator and ionization chamber used for the measurement are then tested to provide support for subsequent experiments.The detection method of the medical accelerator is based on the test method given in the “Guidance Regulation for Medical Electron Accelerator Radiation Sources” JJG589-2008.The radiation quality of the medical accelerator,the uniformity of the radiation field,the symmetry of the radiation field,and the repetition of the dose indication are repeated.The test was carried out to ensure that the medical accelerator used meets the metrological performance requirements;the detection method of the ionization chamber is based on the detection method given in the “Treatment Level Ionization Chamber Dosimeter Verification Protocol” JJG912-2010,and the leakage rate to the ionization chamber and measurement repetition Sex was tested to ensure that the ionization chamber used meets metrological performance requirements.3?The ionization chamber is calibrated by a substitute method in the built reference radiation field to obtain calibration factors for the irradiation amount,and then the water-to-air blocking power ratio,the ionization chamber disturbance correction factor,and the radiation quality disturbance correction factor are performed using the MC method.In the simulation,the water absorbed dose of high-energy photons was finally calculated.The uncertainty of the relevant standard was 2.98%,satisfying the measurement requirements.4.Simulate the impact of individual differences in the ionization chamber on the measurement results.The main reason is that due to technical problems in the production process,the thickness of the ionization chamber wall and the thickness of the balancing cap have a certain error compared with the actual data,and thus the impact on the calculation of the relevant calibration factor used.Through the above experiments,the measurement of the water absorbed dose of high-energy photons for medical accelerators was realized. |
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