VMATにおけるEPID Dosimetryの検討

摘要

Intensity modulated radiotherapy (IMRT)や volumetric modulated arc therapy (VM AT)など高精度放射線治療では，患者ごとに線量検証を実施し，治療精度を担保することが求められている．近年，セットアップの位置検証に用いられるelectronic portal image device（EPID）をquality assurance（QA）や線量検証に応用するEPID Dosimetryの報告が多数なされている．%Recently electronic portal image devices (EPIDs) have been widely used for quality assurance and dose verification. However there are no reports describing EPID dosimetry for Elekta volumetric modulated arc therapy (VMAT). We have investigated EPID dosimetry during VMAT delivery using a commercial software EPIDose with an Elekta Synergy linac. Dose rate dependence and the linac system sag during gantry rotation were measured. Gamma indices were calculated between measured doses using an EPID and calculation made by a treatment planning system for prostate VMAT test plans. The results were also compared to gamma indices using films and a two-dimensional detector array, MapCHECK2. The pass rates of the gamma analysis with a criterion of 3% and 2 mm for the three methods were over 96% with good consistency. Our results have showed that EPID dosimetry is feasible for Elekta VMAT.