Objective:To compare and choose the best method for measuring metabolic tumor volume (MTV) of nasal extranodal natural killer/T-cell lymphoma (ENKTL), evaluate the prognostic value of 18F-FDG PET/CT metabolic parameters and clinical staging/scoring systems for patients with nasal ENKTL, and explore the added value of the two combinations for prognostic prediction. Methods:From January 2016 to September 2022, 44 patients (26 males, 18 females; age (47.5±13.6) years) pathologically diagnosed with nasal ENKTL who underwent 18F-FDG PET/CT imaging before treatment in Union Hospital, Tongji Medical College, Huazhong University of Science and Technology were retrospectively collected. SUV 2.5, SUV 4.0 and 41%SUV max were used as thresholds to measure MTV and total lesion glycolysis (TLG), and the consistency was analyzed by Bland-Altman analysis. The ROC curve analysis was used to compare the prognostic efficiency of different methods and determine the best method. The prognostic values of different clinical factors and clinical staging/scoring systems between groups were evaluated by corrected χ2 test. The independent factors were screened by Cox-regression model, and the combined diagnosis model was constructed by logistic regression. Results:Of 44 patients, 6(13.6%) were dead, with the overall survival (OS) of 32.05(11.77, 64.43) months, and the 2-year and 5-year OS rates of 86.6% and 82.5%, respectively. The mortality of different groups in age (≥60 and <60 years), prognostic index of natural killer cell lymphoma (PINK) score (low- and high-risk), and international prognostic index (IPI) score (low- and high-risk) were significantly different ( χ2 values: 5.02, 4.12, 3.88, all P<0.05). The consistency of MTV measured by different thresholds was good. Among them, the MTV measured by threshold of SUV 2.5 had the highest predictive efficiency with the AUC of 0.737. Multivariate analysis showed that MTV (hazard ratio ( HR)=10.488, 95% CI: 1.864-59.026, P=0.008) was the independent influencing factor of OS. By removing other factors, minimization model was obtained, including MTV and PINK score ( P values: 0.006, 0.048). The prediction model of MTV combined with PINK score improved prognostic efficacy with the AUCs of MTV, PINK score and the combination model of 0.781, 0.741 and 0.912, respectively. Conclusions:MTV measured by threshold of SUV 2.5 has better prognostic predictive value. MTV is the independent prognostic factor for OS in nasal ENKTL patients. MTV combined with PINK score has better prognostic value.