Study Of Clinical Application Of EPID For Volumetric Modulated Arc Therapy

Volumetric modulated arc therapy based on the linear accelerator is the most advanced modern radiotherapy technology.The application could improve the dose distribution of therapeutic target and biological effects of the tumor, reduce the radiation dose of the target with greatly shortening the treatment time and create favorable conditions for carrying out stereotactic body radiation therapy(SBRT).However, the technology is more complex than the traditional intensity modulated radiation therapy(IMRT) at the stages of planning and implementation, so the quality control of VMAT has become an essential daily work of physicists.This study was to develop a efficent method to quality asurance of VMAT technolegy in three aspects of set-up errors and relevant parameters and planning dose with an amorphous silicon electronic portal imaging devices, aiming to analyze the applicable method and characteristics of EPID as a quality control tool. Moreover, the accuracy and efficiency of EPID were evaluated in the clinical application. The research content is as follows. First, the EPID of their own quality control and the relevant dosimetric characteristics were researched to determine that it is enough stable to clinical application.Second, the images of the patients set-up errors was obtained by EPID which are carried out matching with DDR image, and the ability of EPID finding out set-up errors was analyzed. Third, To evaluate the ability and accuracy of EPID, the VMAT's mechanical parameters tests are carried out including multileaf collimator(MLC) positions and precision, e doserate variation and gantry angle rotation Final, the Portal Dosimetry of EPID is used to verify the VMAT planning dosimetry, and the results are compared with results of MatriXX, the capability of EPID in the verification of dosimetry is analyzed.The results show that the precision of set-up errors detection can be improved, and the results are significant on the design of planning tumor volume(PTV) magine.The images of EPID can accurately reflect the VMAT's mechanical parameter deviation, and it can find out less than or equal to 2mm of MLC's leaf by the profile curve and gamma analysis. The 99% planning average pass rate is over 95% in 3%/3mm criterion by EPID. and the average time of 13.3 minutes was significantly less than two-dimensional matrix verification of MatriXX.This study evaluates the capability of EPID in quality control with the three aspects of VMAT QA. Compared with the other QA device,The EPID is reliable and efficient as a tool of quality control, and can be applied in VMAT technology.