SU‐E‐T‐216: Comparison of Volumetrically Modulated Arc Therapy Treatment Using Flattening Filter Free Beams Vs. Flattened Beams for Partial Brain Irradiation

Abstract

Purpose:Flattening Filter Free (FFF) beams offer the potential for higher dose rates, short treatment time, and lower out of field dose. Therefore, the aim of this study was to investigate the dosimetric effects and out of field dose of Volumetric Modulated Arc Therapy (VMAT) plans using FFF vs Flattening Filtering (FF) beams for partial brain irradiation.Methods:Ten brain patients treated with a 6FF beam from a Truebeam STX were analyzed retrospectively for this study. These plans (46Gy at 2 Gy per fraction) were re‐optimized for 6FFF beams using the same dose constraints as the original plans. PTV coverage, PTV Dmax, total MUs, and mean dose to organs‐at‐risk (OAR) were evaluated. In addition, the out‐of‐field dose for 6FF and 6FFF plans for one patient was measured on an anthropomorphic phantom. TLDs were placed inside (central axis) and outside (surface) the phantom at distances ranging from 0.5 cm to 17 cm from the field edge. Paired T‐test was used for statistical analysis.Results:PTV coverage and PTV Dmax were comparable for the FF and FFF plans with 95.9% versus 95.6% and 111.2% versus 111.9%, respectively. Mean dose to the OARs were 3.7% less for FFF than FF plans (p<0.0001). Total MUs were, on average, 12.5% greater for FFF than FF plans with 481±55 MU (FFF) versus 429±50 MU (FF), p=0.0003. On average, the measured out of field dose was 24% less for FFF compared to FF, p<0.0001. A similar beam‐on time was observed for the FFF and FF treatment.Conclusion:It is beneficial to use 6FFF beams for regular fractionated brain VMAT treatments. VMAT treatment plans using FFF beams can achieve comparable PTV coverage but with more OAR sparing. The out of field dose is significant less with mean reduction of 24%.