Oral Mucosa Dose Parameters Predicting Grade ≥3 Acute Toxicity in Locally Advanced Nasopharyngeal Carcinoma Patients Treated With Concurrent Intensity-Modulated Radiation Therapy and Chemotherapy: An Independent Validation Study Comparing Oral Cavity versus Mucosal Surface Contouring Techniques

PURPOSE To determine whether volumes based on the contours of the mucosal surface instead of the oral cavity can be used to predict grade ≥3 acute oral mucosa toxicity in patients with locally advanced nasopharyngeal carcinoma (LANPC) treated with concurrent intensity-modulated radiation therapy (IMRT) and chemotherapy. METHODS AND MATERIALS A standardized method for the oral cavity (oral cavity contours, OCC) and a novel method for the mucosal surface (mucosal surface contours, MSC) were developed for the oral mucosa and prospectively applied to the radiation treatment plans of 92 patients treated with concurrent IMRT and chemotherapy for LANPC. Dose-volume histogram (DVH) data were extracted and then toxicity was analyzed. Receiver operating characteristic analysis and logistic regression were carried out for both contouring methods. RESULTS Grade ≥3 acute oral mucosa toxicity occurred to 20.7% (19/92) of patients in the study. A highly significant dose-volume relationship between oral mucosa irradiation and acute oral mucosa toxicity was supported by using both oral cavity and mucosal surface contouring techniques. In logistic regression, body weight loss was an independent factor related to grade ≥3 acute toxicity for OCC and MSC (P=.017 and 0.005, respectively), and the independent factor of dosimetric parameters for OCC and MSC were V30Gy (P=.003) and V50Gy (P=.003) respectively. In the receiver operating characteristics curve, the areas under V30Gy of the OCC curves was 0.753 (P=.001), while the areas under V50Gy of MSC curves was 0.714 (P=.004); the cut-off value was 73.155% (sensitivity, 0.842; specificity, 0.671) and 14.32% (sensitivity, 0.842; specificity, 0.575), respectively. CONCLUSION DVH analysis of mucosal surface volumes accurately predicts grade ≥3 acute oral mucosa toxicity in patients with LANPC receiving concurrent IMRT and chemotherapy, but in clinical practice the MSC method appears no better than the OCC one.