Identical Quality Assurance For Volumetric Modulated Arc Therapy In Elekta And Varian Machines

Purpose: Volumetric modulated arc therapy (VMAT) has been adopted by manyclinics for its higher delivery efficiency compared to conventional intensity modulatedradiotherapy techniques. Currently, the quality assurance (QA) has remained achallenge in that no identical tests are available for accelerators from different vendors.This study is the first attempt to design identical QA tests for the VMAT technique forVarian and Elekta machines.Methods: Identical procedures testing MLC positions and movements, dose ratevariations, and gantry positions and movement were created for both machines. Theseincluded picket fence (PF), dose rate vs. gantry speed (DRGS) and MLC speed vs. doserate (MLCDR) tests. Deliverable plans for these tests were made with in-house softwarethat was deliverable for linacs from two vendors (Elekta Synergy and Varian Trilogy).The electronic portal imaging device (EPID) was used for these tests. An automatedanalysis method was established and software was created to quantitatively evaluate theresult.Results: The systematic gap position and width errors from PF tests were within0.5mm. We evaluated the detectability of this program for introduced errors down to0.2mm. Linear relationships existed between the introduced errors and measured errors.In the DRGS test,99.8%and100.0%of the intensity deviations from expected profileswere less than3%for the Synergy and Trilogy, respectively. For the MLCDR, theintensity deviations from expected profiles less than3%were100.0%for Synergy and98.1%for Trilogy.Conclusion: Identical test series were created and implemented for VMATaccelerators from two vendors. Test results were reported from both accelerators.Comparable results were obtained from both vendors, enabling uniform criteria to beestablished for VMAT quality assurance.