Radiation-induced nasopharyngeal ulcers after re-irradiation with intensity-modulated radiotherapy in locoregional recurrent nasopharyngeal carcinoma patients: a dose–volume–outcome analysis.

Objective: To analyze the interrelation between radiation dose and radiation-induced nasopharyngeal ulcer (RINU) in locoregional recurrent nasopharyngeal carcinoma (NPC) treated with intensity-modulated radiation therapy (IMRT). Methods: Clinical data were collected from 363 patients with locoregional recurrent NPC who received re-irradiated with definitive IMRT from 2009 to 2017. Twenty-nine patients were diagnosed with RINU. Univariate and multivariate analyses were used to re-evaluate the first and second radiotherapy plans and to identify predictive dosimetric factors. Results: All dosimetric parameters were notably associated with the progression to RINU (p < 0.01) using paired samples Wilcoxon signed rank tests. Multivariate analysis showed that EQD2_ ∑ D80 (dose for 80 percent volume of the unilateral nasopharynx lesion) was an independent prognostic factor for RINU (p = 0.001). The area under the ROC curve for EQD2_ ∑ D80 was 0.846 (p < 0.001), and the cutoff point of 137.035 Gy could potentially be the dose tolerance of the nasopharyngeal mucosa. Conclusions: The sum of equivalent dose in 2 Gy fractions (EQD2) in the overlapping volumes between initial and re-irradiated nasopharyngeal mucosal tissue can be effective in predicting the hazard of developing RINU in NPC patients undergoing radical re‑irradiation with IMRT and we propose a EQD2_ ∑ D80 threshold of 137.035 Gy for the nasopharynx. [ABSTRACT FROM AUTHOR]

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