COMPARISON OF 68Ga-PSMA PET-CT WITH CONVENTIONAL IMAGING IN LOCALIZATION OF BIOCHEMICAL RECURRENT PROSTATE CANCER

Introduction: 68Ga-PSMA PET-CT (PSMA) imaging is being increasingly used in select centers across United States for localizing biochemical recurrence (BCR) in prostate cancer as well as for initial staging. This study investigates the detection rate of PSMA imaging as compared to conventional imaging in the assessment of disease sites in BCR prostate cancer.

Methods: 250 patients were enrolled in a prospective study of 68Ga-PSMA PET-CT imaging for detection of disease sites in BCR prostate cancer. A post-hoc retrospective analysis of 101 patients with available conventional imaging data prior to PSMA imaging was performed. Conventional imaging consisted of computer tomography (59), magnetic resonance imaging (29), bone scan (70) (Sodium Fluoride PET=10, 99mTc-MDP bone scan= 60), and/or other PET-CT scans (23) (11C-choline=7, 11C-acetate=1, FDG=4, Axumin=4, PSMA=7) obtained within 6 months of the current PSMA scan. 68Ga-PSMA PET-CT was performed after oral and IV contrast application unless contraindicated. Clinical reads were used to define positivity on a patient-based analysis.

Results: Mean patient age was 68 years (range 48-83), median PSA 2.4 ng/mL (range 0.05-72.5). 21 of the 101 patients (21%) had positive findings on conventional imaging with all positive findings being confirmed on PSMA imaging. Conventional imaging demonstrated 66 negative results out of which 54 patients (82%) had positive findings on PSMA imaging. 12 patients with negative scans on conventional imaging were confirmed to be negative on PSMA imaging. This results in a concordance of findings in 33 patients out of 87 patients with definitive findings on conventional imaging (38%). In addition, 14 patients had equivocal findings on conventional imaging. PSMA imaging was positive in 12 and negative in 2 patients. Overall, PSMA imaging detected unknown sites of recurrent disease in half of the cohort (54%) and clarified equivocal findings on conventional imaging in 14 % of patients.

Conclusions: PSMA imaging detected unknown sites of disease in more than half of patients with BCR prostate cancer in this cohort. All positive findings on conventional imaging were also positive on PSMA imaging.