Prognostic value of cervical nodal tumor volume in nasopharyngeal carcinoma: Analysis of 1230 patients with positive cervical nodal metastasis

PURPOSE: To investigate the variability and prognostic value of nodal tumor volume (NTV) in nasopharyngeal carcinoma (NPC). METHODS AND MATERIALS: Data on 1230 patients with newly diagnosed stage T1-4N1-3M0 NPC treated with definitive radiation therapy with or without chemotherapy at a single cancer center were reviewed. NTV was determined from dose volume histogram (DVH) data. X-tile analysis was applied to identify the optimal cut-off points for the NTV with respect to regional recurrence-free survival (RRFS). Correlations between the TNM classification system, NTV and RRFS were assessed using a Cox regression model. Cross-validation based on receiver operating characteristic (ROC) curve analysis was applied to compare the prognostic predictive validity of NTV and N categories. RESULTS: Within a median follow-up of 49.9 (range, 1.27–76.40) months, 61/1230 (5%) patients developed regional recurrence and 154 (12.5%) developed distant metastasis. NTV values of 7.2 cc and 35.7 cc were identified as the optimal cut-off points. Patients with larger NTV had poorer prognosis. Compared with the N category, NTV was better at determining RRFS for patients with NPC. Hazard ratios increased with NTV, ranging from 1.86 (95% confidence interval [95% CI], 0.92–3.78) for NTV between 7.2 cc to 35.7 cc, and 3.67 (95% CI, 1.58–8.50) for NTV > 35.7 cc. With both NTV and N category in the same Cox regression model, only NTV remained statistically significant in the RRFS of NPC. The validation results with ROC curves also revealed that, NTV was superior to N category for predicting RRFS with significantly larger area under the ROC curve. CONCLUSIONS: NTV offers important prognostic value for treatment outcomes in NPC, especially regional control. Volumetric analysis of nodal involvement may assist selection of patients with poor prognosis.