Dose Calculation Accuracy for a Flattening-Filter Free Photon Beam Implemented into Oncentra MasterPlan

Abstract: "Introduction For IMRT treatments, removing the flattening filter could be beneficial, as it would decrease the beam-on time required for delivering a certain dose. The aim of this work has been to assess the calculation accuracy obtained when implementing flattening filter free beam data into the treatment planning system Oncentra MasterPlan. Methods An Elekta Precise medical linear accelerator was modified so that it could run a 6 MV flatteningfilter free photon beam, which was implemented into Oncentra MasterPlan. g index evaluations comparing dose distributions in the treatment planning system calculations to exposed films, in order to assess the dose calculation accuracy, were performed for various square fields and a set of prostate IMRT fields. In addition, measured profiles and depth dose curves were compared to line dose distributions extracted from Oncentra MasterPlan. Results The line dose evaluation showed an average and standard deviation of 0.96% and 1.19%, respectively, between calculated and measured dose in field regions of low dose gradient strength and high dose. In the penumbra and build-up regions, the average and standard deviation was 12.01% and 14.15%, respectively, and for the region running along the central axis of the fields, the corresponding deviations were 0.95% and 1.22%. The g index evaluation of IMRT fields showed little difference in calculation accuracy in flattening-filter free mode compared to with the regular beam. All calculated fields matched the measurements, within a 5% dose difference and 2 mm distance-to-agreement acceptance criteria. The g index evaluation of square fields revealed that the pencil beam calculation algorithm calculates the dose more accurately than the collapsed cone calculation algorithm. Conclusion A flattening filter free beam has been successfully implemented into Oncentra MasterPlan and the calculation accuracy has been assessed. The results indicate that prostate IMRT treatments"