SU‐E‐T‐458: Impact of Parameters for Volumetric Modulated Arc Therapy (VMAT) for Rectal Cancer

Purpose:Different parameters Result in different plans. As the developing of volumetric modulated arc therapy for rectal cancer, the purpose of this study was to work out appropriate parameters for the optimization of rectal cancer.Methods:For ten cases which were optimized using Oncentra4.3 version, varying systematically the number of arcs, collimator angle and the delivery time to create different plans. Homogeneity in planning target volume, median dose in the organs at risk and number of monitor units were evaluated for statistical analysis. Measurements were performed with Delt4, taking the delivery time, and compared to the calculation by the gamma method.Results:Plans with collimator 45° were little superior to plans with collimator 0°. Single arc achieved lower homogeneous indices in the planning target volume compared with dual arc, but also requiring less monitor units per fraction dose than dual arc. Single arc needs less monitor units for the treatment; the measured delivery time was reduced from 4 min of dual arc to 2.5 min of single arc. All the plans could achieve good pass rate with gamma method.Conclusion:Some of the parameters have been found as the appropriate sets which can be used as standard for volumetric modulated arc therapy of rectal cancer.