Ga-PSMA PET/CT versus CT and bone scan for investigation of PSA failure post radical prostatectomy.

Objective: To evaluate the use of Gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography (Ga-PSMA PET/CT), compared with conventional CT abdomen/pelvis (CTAP) and whole body single photon emission CT bone scan (BS), for detection of local or distant metastasis following biochemical failure/recurrence in post-prostatectomy patients.

Methods: We conducted a review of our prospectively maintained, institutional database to identify 384 patients with post-prostatectomy biochemical failure/recurrence who underwent PSMA PET/CT, CTAP and BS from February 2015 to August 2017 in Nepean Hospital, tertiary referral centre. The results of the three imaging modalities were analysed for their ability to detect local recurrence and distant metastases. PSMA PET/CT and CTAP imaging were separately performed on the same day and the BS was performed within several days (mostly in 24 h). Difference in detection rates was determined between the modalities and the Chi square test was used to determine significance.

Results: A total of 384 patients were identified with a median prostate-specific antigen (PSA) of 0.465 ng/mL (interquartile range =0.19-2.00 ng/mL). Overall, PSMA PET/CT was positive for 245 (63.8%) patients whereas CTAP and BS were positive in 174 patients (45.3%). A total of 98 patients (25.5%) had local or distant metastasis detected on PSMA only, while 20 patients (5.2%) had recurrences detected on CTAP but not on PSMA PET/CT.

Conclusion: The use of PSMA PET/CT has a higher detection rate of predicted local or distant metastasis compared to CTAP and BS in the staging of patients with biochemical recurrences after radical prostatectomy.