Prognostic efficacy of extensive invasion of primary tumor volume for T3-4 nasopharyngeal carcinoma receiving intensity-modulated radiotherapy

This study aimed to explore the prognostic value of extensive invasion of primary tumor volume for local control in patients with T3-4 NPC receiving intensity-modulated radiotherapy (IMRT). Between January 2009 and December 2015, initial volume of GTV-P, the confined and extensive invasion part of GTV-P (GTV-C and GTV-E) were obtained from 159 prospectively enrolled non-metastatic T3-4 NPC patients. GTV-E included the tumor with infiltration of bony structures at skull base, cervical vertebra, paranasal sinuses or with intracranial extension. GTV-C was calculated by the subtraction of GTV-E from GTV-P. The effects of tumor volume levels on local control rate (LC) were evaluated by Kaplan-Meier method and multivariate analysis. GTV-P (P = 0.015) and GTV-E (P = 0.001) were significantly correlated with local failure, while GTV-C (P = 0.494) was not. Then optimal cut-off values of GTV-P (43 mL) and GTV-E (22 mL) were determined by receiver operating characteristic curve analysis. Patients with small (<22 mL) GTV-E achieved better 5-year LC rate than those with large (≥22 mL) GTV-E (96.3% vs.76.1%, P < 0.001), but no significant difference was found between patients with small (<43 mL) and large (≥43 mL) GTV-P (95.9% vs. 85.5%, P = 0.094). Multivariate analysis also demonstrated large (≥22 mL) GTV-E to be an independent unfavorable prognostic factor for LC (hazard ratio [HR], 3.805; 95% CI, 1.100–13.166; P = 0.035). GTV-E is an independent prognostic factor for LC in T3-4 NPC and may further assist in the optimization of treatment strategies.