Patterns of disease detection using [18F]DCFPyL PET/CT imaging in patients with detectable PSA post prostatectomy being considered for salvage radiotherapy: a prospective trial

Purpose Prostate-specific membrane antigen (PSMA) PET/CT is increasingly used in patients with biochemical recurrence post prostatectomy to detect local recurrence and metastatic disease at low PSA levels. The aim of this study was to assess patterns of disease detection, predictive factors and safety using [F-18]DCFPyL PET/CT versus diagnostic CT in patients being considered for salvage radiotherapy with biochemical recurrence post prostatectomy. Methods We conducted a prospective trial recruiting 100 patients with detectable PSA post prostatectomy (PSA 0.2-2.0 ng/mL) and referred for salvage radiotherapy from August 2018 to July 2020. All patients underwent a PSMA PET/CT using the [F-18]DCFPyL tracer and a diagnostic CT. The detection rates of [F-18]DCFPyL PET/CT vs diagnostic CT were compared and patterns of disease are reported. Clinical patient and tumour characteristics were analysed for predictive utility. Thirty-day post-scan safety is reported. Results Of 100 patients recruited, 98 were suitable for analysis with a median PSA of 0.32 ng/mL. [F-18]DCFPyL PET/CT was positive 46.4% and equivocal 5.2%, compared to 15.5% positivity for diagnostic CT. Local recurrence was detected on [F-18]DCFPyL PET/CT in 28.5%, nodal disease in 27.5% and bony metastases in 6.1% of patients. Both ISUP grade group (p < 0.001) and pre-scan PSA (p = 0.029) were significant predictors of [F-18]DCFPyL PET/CT positivity, and logistic regression generated probabilities combining the two showed improved prediction rates. No significant safety events were reported post [F-18]DCFPyL administration. Conclusions [F-18]DCFPyL PET/CT increases detection of disease in patients with biochemical recurrence post prostatectomy compared to diagnostic CT. Patients being considered for salvage radiotherapy with a PSA >0.2 ng/mL should be considered for [F-18]DCFPyL PET/CT scan.