Abstract: Objective To investigate the value of 68Ga-labeled prostate specific membrane antigen (PSMA) PET/CT for assessing tumor load in primary lesions for risk stratification and predicting metastasis of newly diagnosed prostate cancer (PCa). Methods We retrospectively analyzed the data of 36 patients (mean age 71.3 ± 8.6 years, range 56 to 89 years) with newly diagnosed PCa undergoing 68Ga-PSMA-I&T PET/CT from June 2018 to July 2019. SUVmax and SUVmean of the primary lesions were measured, and the primary PSMA tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA) were automatically measured and calculated in all the patients. The correlations of primary SUVmax, PSMA-TV, and TL-PSMA with PSA and Gleason score (GS) were analyzed, and SUVmax, PSMA-TV and TL-PSMA of the primary lesions were compared among different PCa subgroups. Results SUVmax, PSMA-TV and TL-PSMA of the primary lesions were all correlated with PSA and GS (P<0.05). PCa subgroup analysis showed that SUVmax, PSMA-TV and TL-PSMA were all significantly higher in patients with PSA >20 ng/mL than in those with PSA ≤20 ng/mL (P<0.001), and were higher in patients with a GS ≥8 than in those with a GS ≤7 (P<0.001). PSMA-TV and TL-PSMA were significantly higher in patients with tumor metastasis than in those without metastasis (P<0.001), while SUVmax did not differ significantly with tumor metastasis. SUVmax (P=0.002), PSMA-TV (P<0.001), and TL-PSMA (P<0.001) were all significantly higher in high-risk group than in low-to moderate-risk group. Conclusion PSMA-TV and TL-PSMA of 68Ga-PSMA-I&T PET/CT have potential value in predicting risk stratification and metastasis of newly diagnosed PCa.

Key words: ⁶⁸Ga-PSMA-I&T; prostate cancer; tumor load; risk stratification; metastasis risk; prostate specific membrane antigen