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RapidArc Delivery Performance Using EDR2 Film and EPID Measurement

S Xu

S Xu*, R Ge, W Xu, X Cong, C Xie, H Gong, Chinese PLA General Hospital, Beijing, China

SU-E-T-155 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The Varian RapidArc is a system for volumetric modulated arc therapy (VMAT) technique. To obtain the accuracy,efficiency and reliability of the optimal conformal dose during treatment, RapidArc delivery depends on the controlling capabilities and synchronicity such as variable dose rate, variable gantry speed and dynamic multileaf collimator(DMLC). This study describes the development and implementation EDR2 film and electronic portal imaging device(EPID) during commissioning and quality assurance procedures for RapidArc radiotherapy delivery system.

Methods: The tests were designed to evaluate RapidArc performance using EDR2 film and EPID tools. The accuracy of DMLC position during gantry rotation, the ability to vary and control the dose-rate and gantry speed, the synchronization of variable DMLC speed and dose-rate were examined.

Results: The picket fence test of MLC in stationary gantry and RapidArc modes were implemented. EDR2 film and EPID showed good consistency for obtaining the patterns, and the minimal analysis of leaf accuracy test measured with film was better than 0.4mm with EPID. The synchronicity test, a fully dynamic field, was designed to uniformly irradiate seven parts of a square field using different combinations of gantry speed and dose rate. Comparing with a corresponding open field for the influence of beam flatness and asymmetry, both EDR2 film and EPID were found to yield good results, with a mean deviation of 0.24% vs 0.19%. During evaluating accurate correlated motion of DMLC speed, gantry speed and dose-rates, the dose of four parts in a field showed good agreement, with a mean deviation of 0% vs 0.01%. The analysis of dose patterns was less than 2%.

Conclusion: This study demonstrated that EDR2 film and EPID system can be used as reliable and efficient quality assurance tools for RapidArc delivery performance. Of course, the use of VMAT QA measurement with EPID increases the efficiency of routine QA.

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