Significance of Primary Tumor Volume and T-stage on Prognosis in Nasopharyngeal Carcinoma Treated with Intensity-modulated Radiation Therapy

Objective: The aim of this study was to evaluate the effect of the primary tumor volume on prognosis in nasopharyngeal carcinoma treated with intensity-modulated radiation therapy. Methods: Between August 2003 and April 2005, 112 patients with Stage I-IVB nasopharyngeal carcinoma treated by intensity-modulated radiation therapy were included. Measurement of the primary tumor volume was based on contrast-enhanced computed tomography scans before treatment. A receiver operating characteristics curve was used to determine the best cut-off point of the primary tumor volume. Results: The mean primary tumor volume for 112 patients with nasopharyngeal carcinoma was 33.9 +/- 28.7 ml. Within the framework of UICC T-staging, all patients were divided into four groups according to the primary tumor volume. We call it the volume stage (V1<15.65 ml, V2 = 15.65-24.25 ml, V3 = 24.25-50.55 ml and V4 >50.55 ml). The 5-year overall survival rates for V1, V2, V3 and V4 were 88.5, 83.3, 82.4 and 54.5% (P = 0.014), respectively. The cumulative survival curves for V1, V2 and V3 were very close, but clearly separated from V4. In addition, Cox proportional hazards regression model analysis showed that a primary tumor volume >50 ml was an independent risk factor for radiotherapy (risk ratio = 3.485, P = 0.025). Conclusions: This study demonstrated that the primary tumor volume had significantly impacted on the prognosis of patients with nasopharyngeal carcinoma. We proposed that the primary tumor volume should be considered as an additional stage indicator in the new revision of the clinical stage of nasopharyngeal carcinoma.