Diagnostic Performance of Ga Prostate-specific Membrane Antigen PET/MRI Compared with Multiparametric MRI for Detecting Clinically Significant Prostate Cancer.

Background Gallium 68 (Ga) prostate-specific membrane antigen (PSMA) PET/MRI may improve detection of clinically significant prostate cancer (CSPC). Purpose To compare the sensitivity and specificity of Ga-PSMA PET/MRI with multiparametric MRI for detecting CSPC. Materials and Methods Men with prostate specific antigen levels of 2.5-20 ng/mL prospectively underwent Ga-PSMA PET/MRI, including multiparametric MRI sequences, between June 2019 and March 2020. Imaging was evaluated independently by two radiologists by using the Prostate Imaging Reporting and Data System (PI-RADS) version 2.1. Sensitivity and specificity for CSPC (International Society of Urological Pathology grade group ≥ 2) were compared for Ga-PSMA PET/MRI and multiparametric MRI by using the McNemar test. Decision curve analysis compared the net benefit of each imaging strategy. Results Ninety-nine men (median age, 67 years; interquartile range, 62-71 years) were included; 79% (78 of 99) underwent biopsy. CSPC was detected in 32% (25 of 78). For CSPC, specificity was higher for Ga-PSMA PET/MRI than multiparametric MRI (76% [95% CI: 62, 86] vs 49% [95% CI: 35, 63], respectively; < .001). Sensitivity was similar (88% [95% CI: 69, 98] vs 92% [95% CI: 74, 99], respectively; > .99). For PI-RADS 3 lesions, specificity was also higher for Ga-PSMA PET/MRI than for multiparametric MRI: 86% (95% CI: 73, 95) versus 59% (95% CI: 43, 74), respectively ( = .002). Decision curve analysis showed that biopsies targeted to PSMA uptake increased the net benefit of multiparametric MRI only among PI-RADS 3 lesions. The net benefit of targeted biopsy for a PI-RADS 3 lesion with PSMA uptake was higher across all threshold probabilities over 8%. The net benefit of targeted biopsy was similar for PI-RADS 4 and 5 lesions, regardless of PSMA uptake. Conclusions Gallium 68 prostate-specific membrane antigen PET/MRI improved specificity for clinically significant prostate cancer compared with multiparametric MRI, particularly in Prostate Imaging Reporting and Data System grade 3 lesions. © RSNA, 2021 See also the editorial by Williams and Estes in this issue.