PSMA PET/CT scan in biochemical recurrence post radical prostatectomy - 3.5 year analysis

Aim
68Ga-Prostate-specific membrane antigen (PSMA) PET/CT is an established imaging study useful in the detection of local, nodal and metastatic disease. Biochemical recurrence after radical prostatectomy is defined as > 0.2ng/ML. The aim of this study was to investigate the detection rates with 68Ga-PSMA PET/CT at varying PSA levels in patients with biochemical recurrence to determine the sensitivity in clinical practice.

Method
A retrospective analysis all PSMA PET/CT performed on the Central Coast NSW Australia over 3.5 years (Dec 2015-July 2019). Inclusion criteria used was patients who have had a PSMA PET/CT scan following definitive treatment with radical prostatectomy without adjuvant or salvage radiotherapy or Androgen deprivation therapy. 89 (86 patients) of 606 studies met the criteria and were included in the analysis.

Results
41 out of 89 studies were positive for recurrence with a mean Pre-test PSA of 3.8. Median time since definitive treatment was 2 years (range 0.25 to 25). Detection rates increased with a higher PSA (0% at <.2ng/ML, 27% at .2-.3ng/ML , 27%.3-.5ng/ML, 53% at .5-1ng/ML, 69% at 1-2ng/ML, 88% >2ng/ML). The mean SUV max in positive studies was 9.8. The most common site of recurrence was lymph node metastasis at 56% followed by skeletal and local recurrence at 20% each, soft tissue recurrence was least at 4%.

Conclusion
PSMA PET/CT is useful in detecting early recurrence post radical prostatectomy although at low PSA levels <0.2ng/ML and 0.2ng/ml-0.5ng/ML the sensitivity is low 0-27%. Our results are consistent with previous studies with over 50% positive results with a PSA >0.5ng/ML.