How accurate is Ga68 PSMA PET/ MR in localizing primary prostate cancers compared to multiparametric MRI, Ga68 PSMA PET/CT and whole-mount histopathology-A case series.

Objective: Prostate specific membrane antigen ligands in PET imaging show superior results compared to traditional prostate cancer imaging techniques1. Simultaneous PSMA PET/MR is an emerging modality yielding promising results. We compared the diagnostic accuracy of multiparametric MRI, PSMA PET/ MR and PSMA PET/CT to whole-mount histopathology for localization of primary prostate cancer. Method(s): A prospective database (REDCap-Monash) for patients who underwent MRI in our group urology practice since 2013 was used. 8 patients underwent MRI, PSMA PET/CT, PSMA PET/MR and subsequent radical prostatectomy with whole-mount histopathology. Imaging was reported based on PIRADS Sector Maps, with results analysed by dividing the prostate into 12 sectors; apex/ mid/base in the transverse plane, left/right in the sagittal plane, and anterior/posterior in the coronal plane. Result(s): Whole-mount histopathology revealed significant cancer in 8 patients, with tumour foci detected in 46/96 sectors, with significant cancer defined as greater than or equal to Gleason 3 + 4 = 7. MRI detected lesions in 20 sectors (19 involving tumour foci), no lesion in 76 sectors (27 involving tumour foci). PET/CT demonstrated avidity in 32 sectors (21 involving tumour foci), no avidity in 64 sectors (25 involving tumour foci). PET/MR demonstrated avidity in 22 sectors (all involving tumour foci), no avidity in 74 sectors (24 involving tumour foci). The overall accuracies were 71%, 63% and 75% respectively. Conclusion(s): In this case-series involving highly selected patients, PET/MR outperformed both MRI and PET/CT in accurately detecting significant primary prostate cancer. As a diagnostic technique, pelvic PET/MR is an emerging modality, and as such requires further investigation and cost-effectiveness analysis.