Radiation -Induced Nasopharyngeal Necrosis in LocallyRecurrent Nasopharyngeal Carcinoma Patients after ReRadiotherapy

e18063 Background: Re-radiotherapy (re-RT) is the main treatment for locally recurrent nasopharyngeal carcinoma (lrNPC) patients, and commonly led to radiation-induced nasopharyngeal (NP) necrosis, which was lethal but rare study has focused on it. The aim of this study was to evaluate the cause and impact of radiation-induced NP necrosis in lrNPC patients who received re-RT. Methods: Totally 252 lrNPC patients who received re-RT between January 2013 and December 2020 were retrospectively collected. The inclusion criteria were as follows: (1) no NP necrosis before re-RT; (2) complete medical records, including treatment, clinical and dosimetric information; (3) conventional fractionated radiotherapy. All patients received intensity-modulated radiotherapy ± chemotherapy. Radiation-induced NP necrosis was diagnosed by magnetic resonance imaging and/or electronic nasopharyngoscopy. Dosimetric factors of the planning target volume of primary tumor (PTVp) were extracted from the dose-volume histogram (DVH), which was rescaled to an equivalent dose of 2 Gy per fraction (EQD 2 Gy) using a linear quadratic model. Logistic regression was used to identify the independent prognostic factors for generating the nomogram. Results: With a median follow-up of 44.63 months (inter-quartile range [IQR], 27.70 – 69.20 months), 47.6% of patients (120/252) occurred radiation-induced NP necrosis, which mostly happened within 1 year post re-RT (median [IQR], 5.83 [3.37 – 11.57] months). The 3-year overall survival was 83.0% vs 39.7% ( P＜0.001) in lrNPC patients with or without radiation-induced NP necrosis. Except for the fractionated dose, other dosimetric factors of PTVp were not significantly different between two groups, including D 98 (dose to 98% of PTVp), D 50 , D 2 and homogeneity index (Table). Furthermore, multivariate analysis showed that continuous variable age (HR [95%CI]: 1.04 [1.02 – 1.07], P = 0.003) and tumor volume (HR [95%CI]: 1.02 [1.01 – 1.03], P＜0.001), and fractionated dose > 2.22 Gy (HR [95%CI]: 2.36 [1.32 – 4.21], P = 0.004) were independent factors in predicting radiation-induced NP necrosis, which yielded a C-index of 0.742 (95% CI, 0.682 - 0.803) for OS in the nomogram. Conclusions: The incidence of radiation-induced NP necrosis was high in lrNPC patients who received re-RT. Patients with older age, larger tumor volume or receiving fractionated dose over 2.22 Gy were more easily to suffer NP necrosis, which need to explore novel treatment strategies to improve patients’ survivals. [Table: see text]