[Impact of dynamic parameters on dose delivery accuracy in volumetric modulated arc therapy].

Volumetric modulated arc therapy (VMAT) is an irradiation method in which the multi-leaf collimator (MLC) shape, gantry speed and dose-rate is continuously varied. Gantry speed and dose-rate are treated as specific dynamic parameters (DPs) in VMAT, so there is a need to confirm the influence of DPs on dose distribution. The purpose of this study was to verify the impact of DPs on the accuracy of dose delivery in VMAT. We adopted an irradiation scenario in which DPs were modified from the original plan without making any changes in the dose distribution. We carried out irradiation and measured the dose distributions using a Delta4 diode array phantom, during which we acquired log files that enabled us to calculate DPs. The results showed that dose errors exceeding 1% or geometric errors greater than 1 mm were not produced by modifying the DPs. We were therefore able to verify the impact of DPs on dose delivery accuracy in VMAT.