Dosimetric analysis of radiation-induced brainstem necrosis for nasopharyngeal carcinoma treated with IMRT.

BACKGROUND: Radiation-induced brainstem necrosis (RIBN) is a late life-threatening complication that can appear after treatment in patients with nasopharyngeal carcinoma (NPC). However, the relationship between RIBN and radiation dose is not still well-defined. METHODS: During January 2013 and December 2017, a total of 1063 patients with NPC were treated at Sichuan cancer hospital with IMRT. A total of 479 patients were eligible for dosimetric analysis. Dosimetric parameters of the RIBN, D(max)(the maximum dose), D(0.1c) (maximum average dose delivered to a 0.1-cc volume), D(1cc), D(2cc), D(3cc), D(5cc), D(10cc) and D(mean) (mean does) were evaluated and recorded. ROC curve was used to analyze the area under curve (AUC) and cutoff points. Logistic regression for screening dose-volume parameter and logistic dose response model were used to predict the incidence of brainstem necrosis. RESULTS: Among the 479 patients with NPC, 6 patients were diagnosed with RIBN, the incidence of RIBN was 1.25% (6/479), and the median time to RIBN after treatment was 28.5 months (range 18-48 months). The dose of the brainstem in patients with RIBN were higher than that in patients without necrosis. ROC curve showed that the area under the curve (AUC) of D(max) was the largest (0.987). Moreover, logistic stepwise regression indicated that D(max) was the most important dose factor. The RIBN incidence at 5% over 5 years (TD(5/5)) and 50% incidence over 5 years (TD(50/5)) was 69.59 Gy and76.45 Gy, respectively. CONCLUSIONS: Brainstem necrosis is associated with high dose irritation. D(max) is the most significant predictive dosimetric factor for RIBN. D(max) of brainstem should be considered as the dose limitation parameter. We suggest that the limitation dose for brainstem was D(max) < 69.59 Gy.