Impact of beam configuration on VMAT plan quality for Pinnacle3Auto-Planning for head and neck cases

BackgroundThe purpose of this study was to compare automatically generated VMAT plans to find the superior beam configurations for Pinnacle(3) Auto-Planning and share best practices.MethodsVMAT plans for 20 patients with head and neck cancer were generated using Pinnacle(3) Auto-Planning Module (Pinnacle(3) Version 9.10) with different beam setup parameters. VMAT plans for single (V1) or double arc (V2) and partial or full gantry rotation were optimized. Beam configurations with different collimator positions were defined. Target coverage and sparing of organs at risk were evaluated based on scoring of an evaluation parameter set. Furthermore, dosimetric evaluation was performed based on the composite objective value (COV) and a new cross comparison method was applied using the COVs.ResultsThe evaluation showed a superior plan quality for double arcs compared to one single arc or two single arcs for all cases. Plan quality was superior if a full gantry rotation was allowed during optimization for unilateral target volumes. A double arc technique with collimator setting of 15 degrees was superior to a double arc with collimator 60 degrees and a two single arcs with collimator setting of 15 degrees and 345 degrees.ConclusionThe evaluation showed that double and full arcs are superior to single and partial arcs in terms of organs at risk sparing even for unilateral target volumes. The collimator position was found as an additional setup parameter, which can further improve the target coverage and sparing of organs at risk.