Physical dosimetry of volumetric modulated arc therapy (VMAT) using EPID and 2D array for quality assurance

Outline: To address the correspondence of measured and predicted doses for different malignant tumours utilizing various gamma criteria and QA for confirmation of VMAT with an EPID and 2D array detector. Methods: 24 patients with different malignant tumors were treated by VMAT techniques on Varian IX linear accelerator with 6 MV photon beams. Eclipse treatment planning system (TPS) is used to plan Patient's charts. Gamma Index (GI) variation was compared to the procedure of pre-treatment verification in VMAT plans. Results: The gamma criteria (DD/DTA) of dose difference and distance to agreement for (3%/3 mm), mean +/- SD are gamma( <= 1%) = 99.42% +/- 0.67%, gamma(ma)(x) = 2.11 +/- 0.56 and gamma(avg) = 0.19 +/- 0.05 by EPID, and gamma(%<= 1) = 99.36% +/- 0.53%, gamma(max) = 1.65 +/- 0.45 and gamma(avg) = 0.22 +/- 0.05 by using 2D array detector. Conclusions: Specific QA of VMAT patient (using EPID or 2D array) display great possibility to spare time and to verify individual IMRT fields. 3%/3 mm is the most appropriate of gamma criteria (DD/DTA) for VMAT plans quality assurance. Control charts are a beneficial method for verification assessment for patient specific quality control.