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