Dosimetric Evaluation of a Hybrid Treatment Planning for Whole-Brain Radiation with Hippocampal Sparing

Abstract Purpose To investigate the effect of a Hybrid planning technique which results from combining intensity modulated radiotherapy (IMRT) and volumetric arc therapy (VMAT) for whole brain radiation therapy hippocampal-sparing (WBRT-HS). Methods Three types of plans were made for 15 patients, namely Hybrid, pure IMRT, and pure VMAT and retrospectively compared. All plans were made using the same contours based on the original computed tomography (CT) scans fused with magnetic resonance imaging (MRI). Plan quality was determined by calculating the conformity (CI) and homogeneity (HI) indices of planning target volumes (PTVs). The three types of plans were compared in terms of dose to organs at risk (OARs), number of monitor units (MUs), and treatment time. Results Hybrid plans showed improved homogeneity (p = 0.04) and conformity (p = 0.01) indices compared to IMRT and VMAT plans. In terms of hippocampus sparing, the Hybrid technique showed almost equal D100% and maximum dose (Dmax) values compared to the other techniques, but without statistical significance (p > 0.05); however, there was a significant difference for the left hippocampus, where the IMRT technique obtained the best result (p < 0.001). Regarding the dose delivered to the remaining OARs, MUs and treatment times, all values for the Hybrid plans were between those of IMRT and VMAT. Conclusion Compared to IMRT and VMAT plans, the Hybrid plan allowed a better conformity and homogeneity for the dose distribution in the PTV with intermediate dose values to the OARs.