LAUSR

214 Background: 18F-fluciclovine PET/CT can improve the detection of post-treatment recurrent prostate cancer (PCa). We quantified factors which increase the likelihood of a positive scan, assessed the ability of 18F-fluciclovine to alter treatment plans and identified an optimal PSA cut-off to identify radiographic recurrence. Methods: Patients who received 18F-fluciclovine PET/CT for recurrent PCa (n=78) were analyzed. Treatment changes based on positive scans were tracked. A receiver-operator characteristic (ROC) curve was used to estimate the optimal PSA cut-off for a positive scan. Results: 18F-fluciclovine predicted radiographic recurrence in 67.9% of patients. PSA at scan (p = 0.010), salvage therapy (p = 0.03), any use of ADT (p = 0.016) and number of studies (p = 0.042) were all associated with a positive scan. Alteration of treatment plans occurred in 34/58 (58.6%) patients. Recurrence sites are: 79/120 (65.8%) lymph nodes, 27/120 (22.5%) bone, 11/120 (9.2%) prostatic bed, and 3/120 (2.5%) elsewhere. The most common treatment alteration was directed stereotactic body radiation therapy (SBRT) (16/34, 47%), followed by salvage surgical therapy (4/34, 11.7%) and ADT (3/34, 8.7%).The optimal PSA cut-off was 0.5 with sensitivity of 81.13% and specificity of 78.38% (ROC=0.7880). Conclusions: 18F-fluciclovine PET/CT detected radiographic disease in 67.9% of patients, resulting in alterations in treatment plans in 58.6% of cases. SBRT was the most common alteration in treatment plan. Previous use of salvage therapy or ADT are risk factors and when combined with a PSA >0.5, may be associated with radiographic recurrence. [Table: see text]