Prognostic significance of MRI-based late-course tumor volume in locoregionally advanced nasopharyngeal carcinoma.

BACKGROUND: To validate tumor volume-based imaging markers for predicting local recurrence-free survival (LRFS) in locoregionally advanced nasopharyngeal carcinoma patients, who underwent induction chemotherapy followed by definitive intensity-modulated radiotherapy. METHODS: We enrolled 145 patients with stage III-IVA nasopharyngeal carcinoma in this retrospective study. Pre-treatment tumor volume (V(pre)) and late-course volume (LCV) were measured based on the MRIs scanned before treatment and during the first 3 days in the sixth week of radiotherapy, respectively. The volume regression rate (VRR) was calculated according to V(pre) and LCV. Receiver operating characteristic (ROC) curves were used to identify the cut-off best separating patient subgroups in assessing the prognostic value of V(pre,) LCV and VRR. The Kaplan-Meier method was used for survival analysis. Prognostic analyses were performed using univariate and multivariate COX proportional hazard models. RESULTS: The LCV was 5.3 +/- 0.5 (range 0-42.1) cm(3); The VRR was 60.4 +/- 2.2% (range 2.9-100.0). The median follow-up period was 36 months (range 6-98 months). The cut-off value of LCV determined by the ROC was 6.8 cm(3) for LRFS prediction (sensitivity 68.8%; specificity 79.8%). The combination of LCV and VRR for LRFS prediction (AUC = 0.79, P < 0.001, 95% CI 0.67-0.90), LCV (AUC = 0.74, P = 0.002, 95% CI 0.60-0.88) and V(pre) (AUC = 0.71, P = 0.007, 95% CI 0.56-0.85) are better than T category (AUC = 0.64, P = 0.062, 95% CI 0.50-0.79) alone. Patients with LCV </= 6.8 cm(3) had significantly longer LRFS (P < 0.001), disease-free survival (DFS, P < 0.001) and overall survival (OS, P = 0.005) than those with LCV > 6.8 cm(3). Multivariate Cox regression showed LCV was the only independent prognostic factor for local control (HR = 7.80, 95% CI 2.69-22.6, P < 0.001). CONCLUSIONS: LCV is a promising prognostic factor for local control and chemoradiosensitivity in patients with locoregionally advanced NPC. The LCV, and the combination of LCV with VRR are more robust predictors for patient survival than T category.