${}^{68}$Ga-PSMA PET in prostate cancer. A systematic review and meta-analysis of the observer agreement

The performance of ${}^{68}$Ga-PSMA PET/CT-MR has been evaluated in prostate cancer (PCa), showing significant results. However, even a technically accurate imaging procedure requires a high interobserver agreement in its interpretation to implement in patients' management. This study aims to perform a systematic review and meta-analysis on the interobserver variability in ${}^{68}$Ga-PSMA PET/CT-MR imaging in PCa patients. We conducted a systematic review and meta-analysis on the interobserver variability, including studies: (1) providing Kappa (K) as the inter-observer agreement test or the essential data to calculate it, (2) providing the K confidence interval or the essential crude data to calculate it, (3) measuring K statistic based on the appropriate use criteria for the inter-observer agreement. Twelve studies, providing 1585 ${}^{68}$Ga-PSMA PET/CT-MR studies reviewed by 62 independent readers, were included. In general, the pooled inter-observer agreement was interpreted as substantial for all analyzed groups, including tumoral lesions in the prostate bed, lymphadenopathies, bone metastasis, and soft-tissue metastasis (all between 0.6 and 0.8). The regional lymphadenopathy group (0.74) obtained the highest agreement, while the lowest was for soft tissue metastasis (0.65). This study showed a substantial interobserver agreement in the overall interpretation and detecting locoregional and distant involvement with ${}^{68}$Ga-PSMA PET/CT-MR in PCa patients.