Salvage Radiotherapy Management Decisions in Postprostatectomy Patients with Recurrent Prostate Cancer Based on 18F-Fluciclovine PET/CT Guidance.

This study evaluated the impact of 18F-fluciclovine positron emission tomography/computed tomography (PET/CT) on salvage radiotherapy management decisions in patients with recurrent prostate cancer (PCa) post-prostatectomy. Methods: Patients with detectable prostate-specific antigen (PSA) post-prostatectomy were randomized to undergo either conventional imaging (CI) only (Arm A) or CI plus 18F-fluciclovine PET/CT (Arm B) prior to radiotherapy. In Arm B, positivity rates on CI and 18F-fluciclovine PET/CT for detection of recurrent PCa were determined. Final radiotherapy decisions, a) to offer radiotherapy or not and b) extent of radiotherapy field - prostate bed only or to include pelvis, were based on 18F-fluciclovine PET/CT findings. Radiotherapy decisions before and after 18F-fluciclovine PET/CT were compared. Statistical significance of decision changes was determined using Clopper-Pearson (exact) binomial method. Prognostic factors were compared between patients with and without decision changes. Results: All 165 patients enrolled in the study had standard-of-care CI and were initially planned for radiotherapy. Sixty-three of 79 (79.7%) patients (median PSA 0.33 ng/mL) who underwent 18F-fluciclovine PET/CT (Arm B) had positive findings. 18F-Fluciclovine PET/CT had significantly higher positivity rate than CI for whole body (79.7% vs 13.9%; P <0.001), prostate bed (69.6% vs 5.1%; P <0.001), and pelvic lymph nodes (38.0% vs 10.1%; P <0.001). Twenty-eight of 79 (35.4%) patients had overall radiotherapy decision changed following 18F-fluciclovine PET/CT; 4 of 79 (5.1%) had radiotherapy decisions withdrawn due to extrapelvic disease detected on 18F-fluciclovine PET/CT. Twenty-four of 75 (32.0%) patients with the final decision to undergo radiotherapy had radiotherapy fields changed. Changes in overall radiotherapy decision and radiotherapy fields were statistically significant (P <0.001). Overall mean PSA at PET was significantly different between patients with and without radiotherapy decision changes (P = 0.033). Conclusion:18F-fluciclovine PET/CT significantly altered salvage radiotherapy decisions in patients with recurrent prostate cancer post-prostatectomy. Further analysis to determine the impact of 18F-fluciclovine PET/CT guidance on clinical outcomes post-radiotherapy is in progress.