Background(68)Ga-PSMA Positron Emission Tomography/Computerized Tomography (PET/CT) has shown promising results for the detection of recurrent prostate cancer (RPCa). However, the diagnostic value of this method is yet to be validated. The aim of this study was to determine the influence of clinical and biochemical variables on the detection rate of Ga-68-PSMA PET/CT in patients with RPCa.MethodsThis is a prospective study of 121 patients who underwent Ga-68-PSMA-PET/CT and conventional imaging (CI) for RPCa. Detection rates were analyzed and correlated with various clinical and biochemical variables such as Gleason score GS), androgen deprivation therapy (ADT), trigger PSA (tPSA), PSA doubling-time (PSAdt) and PSA velocity (PSAv).Results(68)Ga-PSMA-PET/CT showed at least one focus of pathological Ga-68-PSMA uptake in 92/121 (76%) of patients. Nodal metastases (in 47% of patients) were the most common site of recurrent disease followed by bones (36%) and prostate (32%). Out of 121 patients, 57 (47%) had only positive findings on PSMA scan verified by biopsy or follow-up. The majority of these lesion were located in the lymph nodes (31/57, 54,5%), which were below the detection limit of CT. Univariate analysis showed higher detection rate of PET/CT with increasing tPSA, PSAv and short PSAdt. Best cutoff for tPSA, PSAv and PSAdt was 0.5ng/ml, 2.25ng/ml/year and 8.65months, respectively. The detection rate of PSMA-PET/CT was higher in patients with high grade tumors (GS>7, 23.7% vs 76.3%) and in patients who were on ADT during of PSMA scan (76.3% vs 96%). In multiple logistic regression analysis, PSAdt and concurrent ADT were identified as predictors of positive Ga-68-PSMA-PET/CT.Conclusion(68)Ga-PSMA-PET/CT is useful for re-staging patients with RPCa and has improved performance compared with CI for disease detection. Detection rates are improved in patients on ADT and with short PSAdt.