The effect of primary tumor volume on the prognosis of nasopharyngeal carcinoma in era of volumetric modulated arc therapy: a propensity score matched cohort study

OBJECTIVE: The role of Primary Tumor Volume (PTV) in Nasopharyngeal Carcinoma (NPC) treated with Volumetric Modulated Arc Therapy (VMAT) is still unclear. The aim of this study was to access the effect of PTV in prognosis prediction of nasopharyngeal carcinoma in era of VMAT. METHODS: Between January 20 and November 2011, 498 consecutive NPC patients with stage I–IVA disease who received VMAT at a single center were retrospectively analyzed. Receiver Operating Characteristic (ROC) was performed to access the cut-off point of PTV. Univariate Kaplan-Meier and multivariate Cox regression analyses were used to evaluate prognostic value for PTV. The Propensity Score Matching (PSM) was used to adjust baseline potential confounders. RESULTS: The 5-year Locol-Regional Failure-Free (L-FFR), Distant Failure-Free Survival (D-FFR), Disease-Free Survival (DFS) and Overall Survival (OS) were 90.6%, 83.7%, 71.5% and 79.3%, respectively. Before PSM, the 5-year L-FFR, D-FFR, DFS, OS rates for NPC patients with PTV ≤ 38 mL vs. PTV > 38 mL were 94.1% vs. 90.4% (p = 0.063), 87.9% vs. 76.3% (p < 0.001), 78.5% vs. 58.5% (p < 0.001) and 86.3% vs. 66.7% (p < 0.001) respectively. Multivariate analysis showed PTV was an independent prognostic factor for D-FFS (p = 0.034), DFS (p = 0.002) and OS (p = 0.001). PTV classified was still an independent prognostic factor for OS after PSM (HR = 2.034, p = 0.025. CONCLUSIONS: PTV had a substantial impact on the prognosis of NPC patients treated with VMAT before and after PSM simultaneously. PTV > 38 mL may be considered as an indicator of the clinical stage of nasopharyngeal carcinoma. LEVEL OF EVIDENCE: III.