Test–Retest Repeatability of Peripheral Ganglion Uptake on 18 F-DCFPyL PET/CT: Implications for Interpreting Benign Uptake on PSMA PET

Repeatability of uptake in benign structures on prostate-specific membrane antigen PET is unexplored and poorly understood. We used a post hoc analysis of a test–retest cohort to assess repeatability of uptake in peripheral ganglia. Methods: Twenty-two patients were included. Spheric volumes of interest were manually placed on the cervical and lumbosacral dorsal root ganglia, the cervicothoracic ganglia, and the celiac ganglia. Repeatability was quantified using intraclass correlation coefficient, within-subject coefficient of variation, and Bland–Altman limits of agreement. Results: Ganglion uptake demonstrated an intraclass correlation coefficient of 0.82 and a within-subject coefficient of variation of 13.1%. Bland–Altman analysis on a relative scale demonstrated that the mean bias was 0.9%, with 95% limits of agreement ranging from −35.8% to 37.6%, broadly comparable to the repeatability of prostate cancer tumors previously reported. Conclusion: The repeatability of uptake in peripheral ganglia on prostate-specific membrane antigen PET scans is similar to the repeatability of uptake in prostate cancer tumors. As such, isolated changes in uptake cannot be used as de facto evidence of a malignant lesion.