The use of 68  Ga-PSMA PET CT in men with biochemical recurrence after definitive treatment of acinar prostate cancer.

INTRODUCTION Early localisation of disease recurrence after definitive treatment of prostate cancer is vital to determine suitability for salvage treatment. Our aim was to further investigate the relationship between prostate specific antigen (PSA) level and detection of suspected cancer recurrence using 68  Ga-PSMA PET/CT in patients with biochemical recurrence after radical prostatectomy (RP) or radiotherapy, particularly at low PSA levels. METHODS This retrospective single tertiary referral institution cohort study of men reviewed the results of 68  Ga-PSMA PET/CT scans for investigation of post RP and post radiotherapy PSA recurrence following primary treatment of prostate cancer. We included men with suspected recurrent prostate cancer based on an elevated post treatment PSA level. The data collected analyzed the relationship of the pre-scan PSA level to the probability of a positive scan finding for recurrent prostate cancer. RESULTS Of the cohort of 532 men, 425 had a previous RP and 107 had prior radiotherapy. The median PSA of the RP group was 0.59 ng/mL and 5.8 ng/mL in the radiotherapy group. In the post RP cohort, the detection rate of 68  Ga-PSMA PET/CT was 11.3% for PSA 0.01 to <0.2 ng/mL, 26.6% for PSA 0.2 to <0.5 ng/mL, 53.3% for PSA 0.5 to <1 ng/mL, 79.1% for PSA 1 to <2 ng/mL and 95.5% for PSA ≥2. Lymph node metastasis post RP was identified in 68% of men with suspected disease recurrence. In the post radiotherapy cohort the detection rate was 33.3% for PSA 0.01 to <0.5 ng/mL, 71.4% for PSA 0.5 to <1 ng/mL, 93.3% for PSA 1 to <2 ng/mL and 100% for PSA ≥2. Local recurrence after radiotherapy was suspected in 71% of the cohort and 40% had suspected lymph node metastasis. CONCLUSIONS To our knowledge, this is largest cohort study of detection rates of 68  Ga-PSMA PET/CT in patients with biochemical recurrence after definitive treatment of prostate cancer, including patients with PSA <0.5 and in a post radiotherapy cohort. Detection of suspected recurrent disease outside the pelvis at low PSA levels will influence the decision for salvage treatment options.