Comparison of [(18)F]PSMA-1007 with [(68)Ga]Ga-PSMA-11 PET/CT in Restaging of Prostate Cancer Patients with PSA Relapse

SIMPLE SUMMARY: Prostate cancer (PC) is one of the most common malignancies in men. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) hybrid imaging can help improve the diagnosis of recurrent PC, in addition to conventional methods such as computed tomography (CT) or magnetic resonance imaging alone. In order to further evaluate the importance of PSMA hybrid imaging, this study identified prostate-specific antigen (PSA) threshold levels for the detection of PSMA-positive lesions in patients with elevated PSA values after therapy. The thresholds were calculated for two different radiopharmaceuticals, PET/CT with [(18)F]PSMA-1007 and [(68)Ga]Ga-PSMA-11, and the results were then compared. In patients who had previously undergone prostatectomy, there was an advantage of PET/CT with [(18)F]PSMA-1007. Overall, however, the results of both methods were similar. The findings may help improve PC detectability in the future and are likely of considerable interest to clinicians by refining algorithms to help determine the clinical approach for the evaluation and treatment of patients with elevated PSA values after therapy. ABSTRACT: This study aimed to compare the diagnostic performance of [(18)F]PSMA-1007 positron emission tomography/computed tomography (PET/CT) ((18)F-PSMA) and [(68)Ga]Ga-PSMA-11 PET/CT ((68)Ga-PSMA) by identifying prostate-specific antigen (PSA) threshold levels for optimal detecting recurrent prostate cancer (PC) and to compare both methods. Retrospectively, the study included 264 patients. The performances of (18)F-PSMA and (68)Ga-PSMA in relation to the pre-scan PSA were assessed by receiver operating characteristic (ROC) curve. (18)F-PSMA showed PC-lesions in 87.5% (112/128 patients), while (68)Ga-PSMA identified them in 88.9% (121/136). For (18)F-PSMA biochemical recurrent (BCR) patients treated with radical prostatectomy (78/128, patient group: F-RP), a PSA of 1.08 ng/mL was found to be the optimal cut-off level for predicting positive and negative scans (AUC = 0.821; 95%, CI: 0.710–0.932), while for prostatectomized (68)Ga-PSMA BCR-patients (89/136, patient group: Ga-RP), the cut-off was 1.84 ng/mL (AUC = 0.588; 95%, CI: 0.410–0.766). In patients with PSA < 1.08 ng/mL (F-RP) 76.3% and <1.84 ng/mL (Ga-RP) 78.6% scans were positive, whereas patients with PSA ≥ 1.08 ng/mL (F-RP) or 1.84 ng/mL (Ga-RP) had positive scan results in 100% and 91.5% (p < 0.001/p = 0.085). The identified PSA thresholds for PSMA-mappable PC lesions in BCR-patients (RP) showed a better separation for (18)F-PSMA with regard to the distinguishing of positive and negative PC-lesions compared to (68)Ga-PSMA. However, the two PSMA PET/CT tracers gave similar overall findings.