The use of 18F-Fluciclovine PET/CT Scan in the detection of recurrent prostate cancer in non-prostatectomy patients

1247 Background: While the diagnostic performance of 18F-FACBC PET/CT imaging in the restaging of patients with biochemical recurrence (BCR) after initial prostatectomy is well documented, its clinical utility in patients with BCR following primary non-prostatectomy treatments is unknown. We aimed to determine detection rate of 18F-FACBC PET/CT scan and the patterns of prostate cancer recurrence in patients with suspected BCR after initial non-prostatectomy treatments, particularly in patients with PSA levels below the accepted Phoenix definition of PSA failure (PSA nadir + 2). Methods: In this single tertiary institution study, we retrospectively enrolled consecutive patients who underwent an 18F-FACBC PET/CT scan between 2017 and 2020 for elevated PSA level following definite initial external beam radiation therapy, brachytherapy and/or cryoablation of prostate cancer. Relevant clinical information including initial treatment, demographic data, PSA level, PSA nadir, PSA kinetic parameter was collected. Receiver operating characteristic (ROC) curve was performed to determine the predictive value of PSA and PSA kinetic parameters for a positive 18F-FACBC PET/CT scan. Results: Sixty patients were enrolled in this study. The median PSA was 3.90 ng/mL. The overall detection rate for suspected recurrent prostate cancer was 85%. A total of 75% (18/24) of men below the Phoenix criteria, with median PSA of 1.7 ng/mL, had scans suggestive of recurrent disease. Local recurrence was the most common site, occurring in 63% (38/60) of patients, with isolated local recurrence in 50% (30/60). The accuracy of 18F-FACBC in patients with isolated local recurrence who had biopsy or follow-up imaging was 88 % (16/18). The 18F-FACBC PET/CT scan detected potential sites of recurrence in 67 % of patients when PSA is < 2 ng/ml. Among PSA and PSA kinetic parameters, the PSA velocity has the highest predictive value of a positive 18F-FACBC PET/CT scan with area under curve of 80 %. Conclusions: 18F-FACBC PET/CT frequently identifies suspected recurrent disease prior to the accepted Phoenix definition of PSA nadir+2. Isolated local recurrence is a common finding which accentuates the importance of early identification of recurrent disease after primary non-prostatectomy treatments with possibility of salvage therapy to improve prognosis.