Prognostic value and predictive threshold of tumor volume for patients with locally advanced nasopharyngeal carcinoma receiving intensity-modulated radiotherapy

BACKGROUND: Gross target volume of primary tumor (GTV-P) is very important for the prognosis prediction of patients with nasopharyngeal carcinoma (NPC), but it is unknown whether the same is true for locally advanced NPC patients treated with intensity-modulated radiotherapy (IMRT). This study aimed to clarify the prognostic value of tumor volume for patient with locally advanced NPC receiving IMRT and to find a suitable cut-off value of GTV-P for prognosis prediction. METHODS: Clinical data of 358 patients with locally advanced NPC who received IMRT were reviewed. Receiver operating characteristic (ROC) curves were used to identify the cut-off values of GTV-P for the prediction of different endpoints [overall survival (OS), local relapse-free survival (LRFS), distant metastasis-free survival (DMFS), and disease-free survival (DFS)] and to test the prognostic value of GTV-P when compared with that of the American Joint Committee on Cancer T staging system. RESULTS: The 358 patients with locally advanced NPC were divided into two groups by the cut-off value of GTV-P as determined using ROC curves: 219 (61.2%) patients with GTV-P ≤46.4 mL and 139 (38.8%) with GTV-P >46.4 mL. The 3-year OS, LRFS, DMFS, and DFS rates were all higher in patients with GTV-P ≤46.4 mL than in those with GTV-P > 46.4 mL (all P < 0.05). Multivariate analysis indicated that GTV-P >46.4 mL was an independent unfavorable prognostic factor for patient survival. The ROC curve verified that the predictive ability of GTV-P was superior to that of T category (P < 0.001). The cut-off values of GTV-P for the prediction of OS, LRFS, DMFS, and DFS were 46.4, 57.9, 75.4 and 46.4 mL, respectively. CONCLUSION: In patients with locally advanced NPC, GTV-P >46.4 mL is an independent unfavorable prognostic indicator for survival after IMRT, with a prognostic value superior to that of T category.