Medical Accelerator Radiation Field Performance Measurement Method Comparison Studies

Since the radiosurgery was proposed in 1950's,radiotherapy has become one of the three means for the treatment of cancer. More and more cancer patients being preoperation,intraoperation and postoperation receive radiotherapy.The goal of radiotherapy is to maximize anti-lesion and protect normal tissues and organs through precisely positioning,precisely planning,precise treatment,。The symmetry of collimator, target position,beam deflection and equipment ageing will affect the radiation field performance and thus the result of radiation therapy.To ensure accurate implementation of the treatment plan,the radiation field performance measurement is a key to the quality of radiation therapy.In this research project, ionizing chamber dosimeter, three types of automatic radiation field scanning systems (blue phantom,RTS-200 and RTS-300) and film dosimeter were used to measure the performance of radiation field,to analyze the results of measurements and to evaluate the consistency among the different devices and methods,so that an accurate, rapid and economical method for measuring radiation field can be chosen.The contents of the research project include:1.Measuring D5,D10, D20,D20/D10 under the two experimental conditions using ionization chamber dosimeter and three automatic scanning systems;2.Measuring the percentage depth dose curves under the two experimental conditions using three kinds of radiation field automatic scanning systems;3.Measuring the off-axis curves under the four experimental conditions using film dosimeter; 4.Measuring the off-axis curves under the twenty experimental conditions using three kinds of radiation field automatic scanning system.The experimental results:1.The D5,D10,D20,D20/D10 were measured under two experimental conditions by using ionization chamber dosimeter and three kinds of automatic scanning systems.In the experimental conditions(1),the maximum deviation of the measurement results was 0.91%;In the experimental conditions (2),the maximum deviation of the measurement results was-0.96%.All deviations were within 1%,It indicated that the measurement results from the ionization chamber dosimeter and three kinds of automatic scanning systems were in good agreement.2. The percentage depth dose curves were measured under two experimental conditions by using three kinds of automatic scanning systems. In the experimental conditions(1),the maximum deviation of the measurement results was-1.26%;In the experimental conditions (2),the maximum deviation of the measurement results was-1.82%.All deviations were within 2%,It indicated that the measurement results from the three kinds of automatic scanning systems were in good agreement.3.The curves of off-axis were measured under two experimental conditions by using ionization chamber dosimeter.In the four experimental conditions,the deviation of the measurement results were all less than 3%(The maximum deviation was 2.87%).It indicated that the measurement results from the film dosimeter and the blue phantom radiotherapy automatic scanning system were in good agreement.4.The curves of off-axis were measured under twenty experimental conditions by three kinds of radiotherapy automatic scanning systems.The maximum deviation of all measurement results under twenty experimental conditions was-1.46%.It indicated that the measurement results from the three kinds of radiotherapy automatic scanning systems were in good agreement.