Value of two-phase [68Ga]Ga-PSMA PET/CT imaging in comparison with optimized delayed imaging in detecting locoregional prostatic metastases

[68Ga]Ga-PSMA PET/CT has gained acceptance for localizing local and distant metastases; However, urinary activity remains a confounding factor in interpreting local metastases. The aim of this study was to evaluate the diagnostic value of two-phase protocol (i.e., early and regular imaging, TPP) in comparison with delayed optimized protocol (i.e., combined regular and delayed post hydration and diuresis images, DOP) to detect locoregional prostatic metastases. Forty-one prostate cancer patients referred for staging (n = 12) or the evaluation of rise in PSA level in prostate cancer (n = 29) were prospectively assessed. In this study, each patient received an early 5-10 min image from pelvic region for two bed position, regular (RP) (60 min) and finally delayed static images. The scan findings were characterized as positive, negative or equivocal. The diagnostic significance of TPP was compared with DOP for prostatic, periprostatic, locoregional lymph nodes and pelvic bone involvement. The diagnostic agreement between DOP and TPP for prostate/prostate bed lesions was comparable with the agreement of DOP and RP (Kappa: 0.78, p < 0.001) vs. (Kappa: 0.8, p value < 0.001). TPP in comparison with RP, had superior sensitivity for prostate/prostate bed lesions (95% vs. 80%). The sensitivity for lymph node metastases, extraprostatic extension and osteometastases was identical between the two protocols. TPP has the potential to replace DOP for the evaluation of prostate/prostate bed lesions; however, there remains instances where delayed imaging is helpful in characterizing the anatomic abnormality especially in the lymph node region.