Dose–volume histogram analysis of brainstem necrosis in head and neck tumors treated using carbon-ion radiotherapy.

Background and purpose We aimed to evaluate the relationship between brainstem necrosis and dose–volume histograms in patients with head and neck tumors after carbon-ion radiotherapy. Material and methods We evaluated 85 patients with head and neck tumors who underwent carbon-ion radiotherapy and were followed-up for ≥12 months. Brainstem necrosis was evaluated using the Common Terminology Criteria for Adverse Events (version 4.0). Results The median follow-up was 24 months, and four patients developed grade 1 brainstem necrosis, with 2-year and 3-year cumulative rates of 2.8% and 6.5%, respectively. Receiver operating characteristic curve analysis revealed the following significant cut-off values: a maximum brainstem dose of 48 Gy (relative biological effectiveness [RBE]), D1 cm 3 of 27 Gy (RBE), V40 Gy (RBE) of 0.1 cm 3 , V30 Gy (RBE) of 0.7 cm 3 , and V20 Gy (RBE) of 1.4 cm 3 . Multivariate analysis revealed that V30 Gy (RBE) was most significantly associated with brainstem necrosis. The 2-year cumulative rates were 33% and 0% for V30 Gy (RBE) of ≥0.7 cm 3 and <0.7 cm 3 , respectively ( p < 0.001). Conclusions The present study indicated that the dose constraints might help minimize brainstem necrosis after carbon-ion radiotherapy. [ABSTRACT FROM AUTHOR]