Study Of Dosimetric Verification For Intensity Modulated Radiation Therapy Quality Control

Intensity Modulated Radiation Therapy is currently one of the advanced radiotherapy technology, widely applied in our country. IMRT treatment demands stringent quality assurance and accurate dose determination, so the job for strict dosimetric verification of IMRT quality control before implementation is of great significance.2-D matrix detector as a new dose verification tool becomes available and has been studied. A kind of2-D ion chamber matrix detector as a radiation dosimeter was selected in this study. First, we evaluated the dosimetric performances of2-D array and performed relevant quality control tests in the photon beams, including dosimetric repeatability, dose response linearity, dose rate dependence and dose measuring uniformity. Then, tests and verifications were performed to evaluate and compare the accuracy of the2-D array with a reference ion chamber. At last,2-D array was used as a tool for dosimetric distribution verification for IMRT.In this study, the reproducibility of the ion chamber array was well within0.3%, medium and long term stability were within0.5%. The array was found to be linear in the dose range of10-250cGy by using6MV,10MV,15MV and60Co photons, and dose nonlinearity was less than0.5%. The output factor was estimated using it and matched very well with reference ion chamber measurements. The response of the detector was found to be independent of dose rate from100MU/min to600MU/min. Also the comparison results showed the maximum deviation of measuring point dose was less than0.6%, and its measuring uniformity was satisfying within1.0%. The dose distribution patterns measured by the array were found to be in good agreement with the calculated dose distribution by TPS between fixed-gantry and unfixed-gantry dosimetric verification.The main characteristics of2-D array are in accord with some requirements of IEC60731. It can be applied to the quality control tests in radiotherapy, and also these test methods of2-D quality control are efficient and valuable. Otherwise, the radiotherapy department should select suitable and available dosimetric verification method for IMRT.