Super Early Scan of PSMA PET/CT in Evaluating Primary and Metastatic Lesions of Prostate Cancer

Ga-68-prostate specific membrane antigen (PSMA)-11 PET/CT has been widely used in the diagnosis of prostate cancer (PCa); however, the urine lead shielding resulting from the urinary metabolism of tracers may obstruct the detection of surrounding metastasis. In this research, the additive value of super early scanning in diagnosing primary lesions and metastasis in the pelvic cavity was evaluated. Firstly, the differentiation efficiency of Ga-68-PSMA-11 PET scanned at 3 min post-injection (min P.I.) was measured in PSMA-positive (22rv1 cells) and PSMA-negative (PC3 cells) model mice. Secondly, 106 patients were scanned at 3 min P.I. for the pelvic cavity and then scanned as a standard protocol at 45 min P.I. In the results, the differential diagnosis of PSMA expression was completely reflected as early as 3 min P.I. for mice models. For patients, when correlated with the Gleason score, the quantitative results of the super early scan displayed a comparable correlation coefficient with the routine scan. The target to bladder ratios increased from 1.44 +/- 2.40 at 45 min to 10.10 +/- 19.10 at 3 min (p < 0.001) for the primary lesions, and it increased from 0.99 +/- 1.88 to 9.27 +/- 23.03 for metastasis. Meanwhile, the target to background ratios increased from 2.21 +/- 2.44 at 3 min to 19.13 +/- 23.93 at 45 min (p < 0.001) for the primary lesions, and it increased from 1.68 +/- 2.71 to 12.04 +/- 18.73 (p < 0.001) for metastasis. In conclusion, super early scanning of Ga-68-PSMA-11 PET/CT added referable information for metastasis detection in order to avoid disturbing tracer activity in the urinary system.