Validation of the Prostate Imaging for Recurrence Reporting (PI-RR) System using 68 Ga prostate-specific membrane antigen-11 (HBED-CC) PET/MRI in biochemical recurrence of prostate cancer: a pilot study.

Objective: To assess the diagnostic performance of Prostate Imaging for Recurrence Reporting (PI-RR) system using 68 Ga prostate-specific membrane antigen (PSMA)-11 (HBED-CC) PET/MRI in prostate cancer (PCa) patients with biochemical recurrence (BCR).

Methods: PET/MRI data of 31 PCa patients [17 with radical prostatectomy (RP) and 14 with radiotherapy (RT)] with BCR were retrospectively analyzed. All patients underwent PSMA PET/MRI and multiparametric prostate MRI (mpMRI). Images were evaluated using PI-RR system for mpMRI and the European Association of Nuclear Medicine standardized reporting guidelines (E-PSMA) for PET, with PI-RR and E-PSMA scores dichotomized as ≤2 negative and ≥3 positive for recurrence. Diagnostic performances were assessed using expert-based ground truth establishment.

Results: Sensitivity, specificity, and accuracy were 64.7%, 85.7%, and 74.2%, respectively, for PET and 70.6%, 100%, and 83.9%, respectively, for PI-RR. While PI-RR did not reveal any false positive lesions, five patients with false negative PI-RR results were also negative with PET. In patients with RP, sensitivity, specificity, and accuracy were 44.4%, 100%, and 70.6%, respectively, for PET and 55.6%, 100%, and 76.5%, respectively, for PI-RR. For patients with RT, these values were 87.5%, 66.7%, and 78.6%, respectively, for PET and 87.5%, 100%, and 92.9%, respectively, for PI-RR. There was no significant performance difference between PET or PI-RR in all patients ( P = 0.564), patients with RP ( P = 0.317), or RT ( P = 0.157).

Conclusion: 68 Ga PSMA PET evaluation with E-PSMA and mpMRI interpretation with PI-RR have similar diagnostic performance for detection of local recurrence after RP or RT in PCa.