Validation of the PSMA PRIMARY Scoring System and Comparison to an E-PSMA Likert System for [68Ga]Ga-PSMA-11 PET/CT Interpretation in Men With Suspected Radiorecurrent Prostate Cancer.

BACKGROUND: To validate the recently published 5-point PRIMARY scoring system against a 5-point European Association of Nuclear Medicine (E-PSMA) Likert system for the detection of intraprostatic recurrence for patients undergoing [68Ga]Ga-PSMA-11 PET/CT who have previously received radiotherapy for prostate cancer as their primary treatment. PATIENTS AND METHODS: Thirty-five patients from one centre were investigated for suspected radiorecurrence between 2016 and 2022. All patients underwent multiparametric MRI and [68Ga]Ga-PSMA-11 PET/CT for staging, then prostate biopsy. Analyses were performed at the hemi-gland level. Two expert readers, blinded to other clinical, pathologic, and radiologic data, independently assigned each hemi-gland an E-PSMA Likert and PRIMARY score. Outcomes were comparative diagnostic accuracy metrics and interreader agreement for each system at the hemi-gland level. Scores of 3-5 were considered suspicious for intraprostatic cancer. RESULTS: Of 70 hemi-glands, 43 (61%) had cancer on biopsy. Area under the curve was high and not statistically significantly different between systems (E-PSMA Likert: 0.84; 95% CI: 0.74-0.92; PRIMARY: 0.82; 95% CI: 0.71-0.91; P = 0.7). Sensitivity for E-PSMA Likert was 0.89 (95% CI: 0.78-0.96), not statistically different compared with the PRIMARY system (0.79; 95% CI: 0.67-0.89; P = 0.3). Specificity for the E-PSMA Likert system was 0.67 (95% CI: 0.46-0.86), not statistically different compared with the PRIMARY system (0.78; 95% CI: 0.60-0.91; P = 0.1). There was substantial interreader agreement between each reader for both E-PSMA Likert (κ = 0.65; 95% CI: 0.44-0.83) and PRIMARY systems (κ = 0.74; 95% CI: 0.59-0.90). CONCLUSIONS: In patients with biochemical recurrence after primary radiotherapy for prostate cancer, both the 5-point PRIMARY and E-PSMA Likert scoring systems score demonstrated good performance and substantial interreader agreement between experts for the detection of intraprostatic recurrences.