Comparing Volumetric-modulated Arc Therapy and Intensity-modulated Radiation Therapy for Hippocampus-sparing Whole-brain Radiotherapy: A Dosimetric Evaluation

A BSTRACT Aim: Critical technical issues related to contouring and treatment planning arise while trying to protect the hippocampus (HC) from radiation during cranial irradiation. In this article, we present our preliminary results from treating patients with brain metastases using whole-brain radiation with HC sparing. Methods: Twelve patients previously treated with whole-brain radiotherapy with hippocampal sparing were included in this retrospective study. The HC was contoured, and hippocampal avoidance regions were created using a 5-mm volumetric expansion around the HC. A total of 24 linear accelerator-based intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) treatment plans were generated for a prescription dose of 30 Gy in 10 fractions. Results and Discussion: On average, the hippocampal avoidance volume was 17 cm 3 , occupying 1.32% of the whole-brain planned target volume. VMAT spared the HC, with a median dose of 16.6 Gy and a maximum dose of 23.5 Gy. IMRT spared the HC, with a median dose of 17.7 Gy and a maximum dose of 19.5 Gy. On a per-fraction basis, the mean dose to the HC was reduced by 55% to 16.28 Gy using VMAT and by 59% to 17.83 Gy using IMRT. Target coverage and homogeneity were acceptable with both IMRT and VMAT modalities. No statistically significant ( P < 0.05) difference was found with different modalities in target coverage. Conclusions: Modern IMRT/VMAT techniques allow for the sparing of the HC with acceptable target coverage and homogeneity. Our novel use of gantry, collimator, and couch orientations allowed the plan to satisfy RTOG 0933 specified criteria.