Sci-Fri PM: Delivery - 05: A complete set of VMAT machine-specific QA tests using EPID

During a VMAT (Volumetric Modulated Arc Therapy) radiation delivery, various machine parameters (gantry position and speed, MLC leaves position, dose rate, etc) have to be highly synchronized and coordinated. To ensure that all of the machine components are effectively operating together requires unique machine-specific quality assurance (QA) tests. The purpose of this work is to describe a complete set of VMAT machine-specific QA tests using Electronic Portal Imaging Device (EPID). To address the need for VMAT machine-specific QA tests, Varian has recommended 6 EPID-based tests for commissioning and QA of RapidArc™ capable machines. Recent studies have identified that these Varian tests do not define a complete set of tests needed for adequate commissioning and machine-specific QA of RapidArc machines. The goal of this work is twofold: a) to report and discuss the results of the original 6 Varian's EPID-based tests, and b) to extend the original set by adding 2 more EPID-based tests, which results in a more complete and comprehensive set of tests. We have demonstrated that the Varian EPID-based QA tests can be used to verify that the synchronization of Dose Rate, Gantry Speed and MLC Leaves speed is generally to within 1.5% during a RapidArc delivery. Also, the gantry rotation does not have any significant effect on MLC leaves positional accuracy during a RapidArc delivery. Finally, we have introduced a new EPID-based QA test, which can be used to verify that the angular accuracy of the gantry position during a RapidArc delivery is to within ∼1 degree.