Radiation-induced nasopharyngeal ulcers after intensity modulated radiotherapy in primary nasopharyngeal carcinoma patients: A dose-volume-outcome analysis.

OBJECTIVE: This is a retrospective dose-volume-outcome analysis of radiation-induced nasopharyngeal ulcers after intensity modulated radiotherapy in primary nasopharyngeal carcinoma (NPC) patients, with the aim to determine how the radiation doses to nasopharynx influence the occurence of radiation-induced nasopharyngeal ulcer (RINU) and predict the most serious complication of radiotherapy for NPC. METHODS: Data from 6023 consecutive and nonselected histologically proven primary NPC patients treated with definitive IMRT were collected and 25 patients were diagnosed with nasopharyngeal ulcer and met the diagnosis criteria of RINU. Predictive dosimetric factors were identified by using univariate and multivariate analysis. RESULTS: Paired samples t-tests showed all dosimetric factors were significantly correlated with the development of RINU, and these factors were associated with each other closely. (P < 0.001) Multivariate analysis revealed D3cc (dose to 3 mL of the nasopharynx) was an independent predictor for RINU (P = 0.01); the area under the ROC curve for D3cc was 0.87 (P < 0.001), and the cutoff point 73.67 Gy may be the dose tolerance of the nasopharynx. The primary tumor location, distribution of high dose regions and the location of RINU were consistent. CONCLUSIONS: The study indicates that radiation-induced nasopharyngeal ulcer is consistent with primary tumor location and 'hottest spots' regions and we suggest a D3cc limit of 73.67 Gy for the nasopharynx. Physicians should be cautious of such 'hot spots' in the nasopharynxduring IMRT treatment plan optimization, review and approval to avoid the most serious complication of radiotherapy for NPC.