Test-Retest Reproducibility of Conventional Quantitative Parameters on PSMA-targeted 18F-DCFPyL PET/CT in Patients with Metastatic Prostate Cancer

1317 Objectives: Prostate-specific membrane antigen (PSMA)-targeted 18F-DCFPyL has proven to detect metastatic prostate cancer (PC) with high accuracy. In this study, we evaluated 18F-DCFPyL test-retest reproducibility of conventional quantitative parameters in widespread disease. Methods: In a prospective clinical trial (NCT03793543), 23 patients with histologically proven PC underwent two 18F-DCFPyL PET scans within 7 days (mean 3.7, range 1 to 7d). Lesions in bone, lymph nodes and other organs were manually segmented on both scans and quantitative parameters were assessed (mean [SUVmean] and maximum [SUVmax] standardized uptake values, PSMA-tumor volume [PSMA-TV] and total lesion PSMA [TL-PSMA, SUV x TV]). Repeatability of quantification was determined using correlations and within-subject coefficient of variation (wCOV, in %; 30% unacceptable reproducibility). Results: In total, 229 lesions (176 bone, 38 lymph nodes, 15 others) were delineated in both scans. For all investigated parameters, a high inter-scan correlation was found (R2≥0.98). Analyzing all lesions, the wCOVs for SUVmax and SUVmean were 12.1% and 7.3%, respectively, indicating good to excellent reproducibility for PSMA expression derived by SUV. The wCOV of LN, however, were significantly lower relative to those derived from osseous lesions (SUVmean: LN, 3.8% vs. skeleton, 7.8%, p