EPID dosimetry for IMRT and VMAT PSQA

Abstract

Aim The aim of this project is to investigate if the Electronic Portal Imaging Device (EPID) would be suitable for Patient Specific Quality Assurance (PSQA) of intensity modulated radiation therapy (IMRT) & volumetric modulated arc therapy (VMAT). Materials and methods The EPID was compared against the MapCHECK detector using 5 clinical IMRT and VMAT plans. All plans were measured using an EPID from an Elekta synergy machine and the MapCHECK diode array. Sun nuclear software (SNC patient) was used to acquire and process measured dose distributions from the EPID and MapCHECK and comparisons were made using pass rate ⩾90% for 2%/2 mm and ⩾95% for 3%/2 mm with 10% threshold, for Gamma evaluation, distance to agreement (DTA) and isocentric dose to treatment planning system (TPS). A physics model (EPIDose) was created following manufacturer recommendations in order to convert the EPID panel pixel information to dose using a four step approach. Results Clinical cases for IMRT plans shows the average pass rate of all fields is 98.92% for 2%/2 mm and 99.58% for 3%/2 mm for EPID, and 99.08% for 2%/2 mm and 99.78% for 3%/2 mm for MapCHECK. Conclusion The PSQA results for MapCHECK and EPID provides acceptable agreement for clinical criteria. The sensitivity of EPID panel provide more information for EPIDose dosimetry with relative short time for setup and friendly use, this is make the EPID panel more usable as dosimetry technique, compare to MapCHECK that required to more time for setup.