SU‐E‐T‐221: Evaluation of Quality Assurance for Rapid Arc Treatments Using EPIQA Software

Purpose: To evaluate the patient specific quality assurance of Rapid Arc treatments using EPID and EpiQA software. Methods: Eclipse TPS is used for the creation and calculation of patient and verification plans. The treatments were delivered on aS1000 EPID attached to the Varian Clinac iX Linear Accelerator. EpiQA software supplied by the EPIdos is used for the analysis of calculated and measured dose maps. In this retrospective study 75 Rapidarc treatment plans consisting of 150 arc fields were considered from three different sites of 25 plans each namely head & neck, pelvis and brain. All plans were treated with 6 MV photons with two arcs and QA measurements acquired with Portal Vision aS1000 and analyzed by EpiQA software. To evaluate the QA results, we used Gamma agreement Index (GAI). GAI represents the percentage of the field area with gamma value greater than 1.0 to the gamma criteria of 3mm DTA and 3% Dose Difference. Results: Calculated mean values and standard deviations are 1.95 ± 1.25, 2.44 ± 1.35 and 2.69 ± 1.13 for Brain, Pelvis and Head & Neck respectively. It is noted that all the results were well within 95% of pass criteria of gamma agreement index. We found that the mean GAI values for head & neck and pelvis plans are greater than that of brain plans. This deviation may be attributed due to the variations in the geometry of the field, volume of irradiation, depth of penetration and complexity of planning objectives (more critical organs) etc. However further data of measurements is needed for further evaluation. Conclusion: Since all the plans were passed the GAI and the results are comparable with phantom studies, we conclude that the portal dosimetry can be used conveniently to carryout patient specific QA measurements of Rapidarc plans.