Novel [F-18]siPSMA-14 shows favourable kinetics and high interobserver agreement in staging of prostate cancer patients

1328 Aim: The novel PSMA-specific PET-Tracer [F-18]siPSMA-14 showed promising biodistribution and tumour uptake in prostate cancer (PCa) bearing mice. Our aim was to analyze its clinical performance in primary- (PS) and restaging (RS) of PCa patients by analyzing biodistribution, detection rates and interobserver variability at 90min p.i.. Methods: In 134 patients with PCa (69.7 ± 7.5 years; GS 6-9; median (range) PSA 2.36 (0.08-1898) ng/ml) [F-18]siPSMA-14 PET/CT was performed for PS (40%, 54/134) or RS (60%, 80/134). Images were acquired 90min p.i. of 374.2 ± 8.1 MBq without forced diuresis. Findings in different lesion localizations (prostatic lesions (PL), lymphatic lesions (LN), bone lesions (B), visceral lesions (P)) were rated using a 5-scale-system ranging from C1 (definitely benign) to C5 (definitely malignant). Images were evaluated by two nuclear medicine physicians and radiologists (R1, R2). Agreement between R1 and R2 was measured by Cohens-Kappa. Biodistribution measurements were performed using SUVmean in a fixed size region of interest (ROI) to assess the physiological and pathological tracer accumulation. For contrast evaluation target/non target ratios (TTR) were measured by comparing tumour- and background uptake. Results: In consensus reading, the detection rate was 94% (51/54) and 86% (69/80) in PS and RS respectively. In subgroups with PSA values of 0-0.5, 0.5-1, 1-5 and >5 ng/ml detection rates were 68% (19/28), 89% (17/19), 94% (30/32) und 98% (54/55). Interobserver agreement for PL, LN, P was high with Kappa-values of 0.85, 0.75, 0.86 and with 0.51 moderate for B. TTR for PL (n = 88), LN (n = 68), B (n = 51), P (n = 3) were high with 9.3, 11.6, 14.3, 14.6; PL-uptake ranged above urinary bladder uptake with an average SUVmean ratio of 1.7. Conclusions: [F-18]siPSMA-14-PET/CT performs comparably concerning detection rates to other PSMA-binding radiopharmaceuticals with high interobserver agreement and excellent contrast. A major advantage is good performance and image quality adjacent to the urinary bladder even without forced diuresis which is of high relevance for detection of loco-regional tumour recurrence.