Interobserver and intraobserver agreement for equivocal lesions in Ga-68 PSMA PET/CT according to PSMA-RADS 2.0 criteria.

Objective: This study aims to systematically evaluate the inter- and intra-observer agreement regarding lesions with uncertain malignancy potential in Ga-68 PSMA PET/CT imaging of prostate cancer patients, utilizing the PSMA-RADS 2.0 classification system, and to emphasize the malignancy evidence associated with these lesions.

Methods: We retrospectively reviewed Ga-68 PSMA PET/CT images of patients diagnosed with prostate cancer via histopathology between December 2016 and November 2023. Seventy-six patients and 98 target lesions, classified with PSMA-RADS scores 3A-3D by an experienced nuclear medicine specialist, were included. Three observers (two experienced and one less experienced nuclear medicine physician) evaluated the lesions at two different time points, three months apart, in a blinded manner. Intra-observer agreement was assessed using Cohen's kappa, while inter-observer agreement was analyzed using Fleiss' kappa.

Results: All observers demonstrated significant intra-observer agreement, with percentages ranging from 67.3 to 80.6% and kappa values between 0.62 and 0.76. The highest intra-observer agreement was noted for bone lesions, while non-regional lymph nodes exhibited the lowest agreement. For inter-observer assessments, moderate agreement was observed across all lesions (Fleiss k = 0.51), with the highest agreement in regional lymph nodes and the lowest in non-regional lymph nodes and bone lesions. Follow-up results indicated malignancy detection rates of 63.4% for 3A, 47% for 3B, 44.5% for 3C, and 41.4% for 3D scored lesions.

Conclusions: The PSMA-RADS classification system demonstrated substantial intra-observer agreement and moderate inter-observer agreement for lesions with uncertain malignancy potential, supporting its clinical applicability. However, notable variability and limitations in reporting bone lesions, non-regional lymph nodes, and lung lesions were observed among readers. The ambiguous nature and management of PSMA-RADS 3 lesions underscore the need for further research to enhance risk stratification.