Identical Quality Assurance for Volumetric Modulated Arc Therapy in Elekte and Varian Machines
J Wang1*, Y Xiao2, W Hu1, (1) Fudan University Shanghai Cancer, Shanghai, Shanghai, (2) Thomas Jefferson Univ Hospital, Philadelphia, PA,WE-E-141-6 Wednesday 2:00PM - 3:50PM Room: 141
Purpose:Volumetric modulated arc therapy (VMAT) has been adopted by many clinics for its higher delivery efficiency than other conventional intensity modulated radiotherapy techniques. Currently, no identical quality assurance (QA) tests are available for different vendors. This study is the first attempt to design identical QA tests for the VMAT technique for Varian and Elekta machines.
Methods:Procedures testing MLC positions and movements, dose rate variations, gantry positions and movements were created. These include picker fence (PF), dose rate vs. gantry speed (DRGS) and MLC speed vs. dose rate (MLCDR) tests. Deliverable plans for these tests were made with in-house software that was deliverable for linacs from two vendors (Linac1 for Elekta and Linac2 for Varian). The electronic portal imaging device (EPID) was used to detect these tests. An automated analyses method was established and software coded to quantitatively evaluate the result.
Results:The systematic gap position and width errors from PF tests were within 0.5mm. We evaluated the detectability of this program for introduced errors down to 0.2mm. Linear relationships existed between the introduced errors and measured errors. In the DRGS test, 99.8% and 100.0% of the intensity deviations from expected profiles were less than 3% for the Linac1 and Linac2, respectively. For the MLCDR, the intensity deviations from expected profiles less than 3% were 100.0% for Linac1 and 98.1% for Linac2.
Conclusion:Identical test series were created and implemented for VMAT accelerators from two vendors. Test results were reported from both accelerators. Comparable results were obtained from both vendors, and enabling uniform criteria to be established for VMAT quality assurance.