Pre-treatment quality assurance of 220 Rapidarc plans analyzed with EpiQA software

Abstract

Introduction Delivery complexity of volumetric modulated arc-therapy (VMAT) requires a pre-treatment verification process. Electronic portal imaging based on a-Si flat panels are utilized for dosimetric purposes mainly for IMRT pre-treatment verification (QA). Purpose This work is a retrospective analysis of a large dataset of RapidArc routine pre-treatment QA. We report results and analysis of our procedure that combines EPID images and EpiQA commercial software for dose distribution reconstruction. Materials and methods Dose distribution of 220 patients treated with a VMAT technique on Varian DHX-2100 were analyzed. Tumor sites of selected patients were: 70 esophagus, 100 head-neck and 50 lung. The detector reading, for each arc, is converted to a dose map and compared with the TPS (Eclipse) dose distribution, calculated with a virtual water-phantom (0,125 cm calculation grid). Gamma evaluation index was performed to quantitatively compare measured and calculated results using 3%-3 mm, 4%-3 mm and 4%-4 mm agreement criteria. Results Good result were found for all districts. The average values of G 1,5, probably due to the higher modulation. Conclusion EPID images and EpiQA software use for pre-clinical verification show a very good agreement between calculated and measured dose. This QA procedure is easy also in complex treatments such as VMAT. We plan to investigate this study with a calculation grid of 0,25 cm, obtaining a considerable time sparing. Furthermore we would like to compare results obtained with EpiQA software with other systems for pre-treatment QA. Disclosure All authors disclose any financial and personal relationships with other people or organizations that could inappropriately bias this presentation.