Room: AAPM ePoster Library
Purpose: purpose of this study was to develop and implement quality assurance (QA) programs for the Halcyon linac (Varian Medical Systems, Palo Alto, CA) and to evaluate the stability over one year.
Methods: programs were developed according to AAPM Task Group 142. In the daily QA program, x-ray output constancy and registration accuracy were evaluated using a two-dimensional array detector and a cube phantom in addition to the system test. In the monthly QA program, an electronic portal imaging device (EPID) based procedures were developed for mechanical and dosimetric tests. Off-axis factors (OAFs) for open fields with fixed multi leaf collimator (MLC) sequences were obtained using EPID and compared to the baseline. In the annual QA program, depth dose and profiles were measured with a water tank and the constancy of beam quality was evaluated. Gantry angle dependency for the output and the OAFs for open fields with and without fixed MLC sequences was evaluated.
Results: the daily QA, the x-ray output constancy was within ±1 %. The registration accuracy was less than 0.5 mm in translational shifts. In the monthly QA, the isocenter size for MLC and gantry rotation was about 0.5±0.3 mm and 0.4±0.2 mm on average over ten months, respectively. The difference of the OAFs for open fields using fixed MLC sequences from the baseline was about 0.3 % in the cross- and in-plane. In the annual QA, there was no significant change in the evaluation of beam quality. The gantry angle dependency of the output at the isocenter was 0.2 % at most.
Conclusion: developed QA programs were useful for the Halcyon linac. Good machine stability was obtained.