The Feasibility of Sparing the Hippocampus and Hypothalamic -Hypophysial Axis During Whole Brain Radiotherapy: A Dosimetric Study

Abstract

We aimed to investigate the feasibility of simultaneously sparing the hippocampus and hypothalamic-hypophysial axis (HHA) during whole brain radiotherapy (WBRT) using helical tomotherapy. Images of totally 12 patients were analyzed. Hippocampi and HHA were delineated according to available guidelines. First, radiotherapy plans were analyzed according to dose constraints of the Radiation Therapy Oncology Group-0933 for 30 Gy (3 Gy/fr). Second, dose constraints were decreased by 1/6 to simulate the 25 Gy prophylactic cranial irradiation practice. The mean D98% and D2% was 25.9 +/- 0.85 Gy and 35.0 +/- 1.32 Gy, and 21.4 +/- 0.40 Gy and 30.5 +/- 1.33 Gy for planning target volumes in the original and modified protocol plans, respectively. The D loo96 and Dmax for the hippocampus was 8.1 +/- 0.47 Gy and 15.7 +/- 0.84 Gy in the original and 7.1 +/- 0.68 Gy and 13.2 +/- 1.08 Gy in the modified protocol, respectively. The mean doses for the hypothalamus and hypophysis was 12.6 +/- 0.76 Gy and 11.4 +/- 1.22 Gy in the original and 10.8 +/- 1.38 Gy and 9.8 +/- 1.50 Gy in the modified plans, respectively. This study demonstrated the feasibility of sparing the hippocampus and HHA simultaneously during WBRT with helical tomotherapy regarding target dose coverage and dose constraints suggested by the literature.