Impact of Control Point Angular Separation on the Dosimetric Accuracy of VMAT Plans

Method and Materials: As a starting point we considered 142 clinical VMAT plans optimized by Oncentra Masterplan (Nucletron, Elekta) using our standard parameters: 4 control point separation and 5mm/deg leaf motion constraint (in 10 cases a 10 mm/deg constraint was required for a good plan quality). All plans were delivered by a 6 MV Linac (Elekta Synergy) to a Delta4 phantom (Scandidos) for patient specific QA; local gamma index analysis (3%,3mm; 3%, 2mm and 2%, 2mm) permitted to compare delivered and calculated doses. For each plan the average leaf travel (LT) was computed and Pearson’s correlation analysis performed between gamma passing rates and LT. A Modulation Complexity Score (MCS) adapted to VMAT [1,2] was also calculated to score plan complexity.