917P - Radiation-induced nasopharyngeal necrosis in locally-recurrent nasopharyngeal carcinoma patients after re-radiotherapy

Background

Re-radiotherapy (re-RT) is the main treatment for locally recurrent nasopharyngeal carcinoma (lrNPC) patients, and commonly leads to radiation-induced nasopharyngeal (NP) necrosis. 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; (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. 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. 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 D₉₈ (dose to 98% of PTVp), D₅₀, D₂ and homogeneity index. Furthermore, multivariate analysis showed that age (HR [95%CI]: 1.04 [1.01 – 1.07], P = 0.004), tumor volume (HR [95%CI]: 1.03 [1.02 – 1.05], P＜0.001), and fractionated dose > 2.22 Gy (HR [95%CI]: 2.29 [1.28 – 4.09], P = 0.005) were independent factors in predicting radiation-induced NP necrosis, which yielded a C-index of 0.742 (95% CI, 0.681 - 0.803) for NP necrosis 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 greater risk of NP necrosis. There is a need to explore novel treatment strategies to improve patient survival.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Sun Yat-sen University Cancer Center.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.