Detection and localisation of primary prostate cancer using ⁶⁸gallium prostate-specific membrane antigen positron emission tomography/computed tomography compared with multiparametric magnetic resonance imaging and radical prostatectomy specimen pathology

Objective: To compare the accuracy of ⁶⁸gallium prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA PET/CT) with multiparametric MRI (mpMRI) in detecting and localising primary prostate cancer when compared with radical prostatectomy (RP) specimen pathology. Patients and methods: Retrospective review of men who underwent ⁶⁸Ga-PSMA PET/CT and mpMRI for primary prostate cancer before RP across four centres between 2015 and 2018. Patients undergoing imaging for recurrent disease or before non-surgical treatment were excluded. We defined pathological index tumour as the lesion with highest International Society of Urological Pathology Grade Group (GG) on RP specimen pathology. Our primary outcomes were rates of accurate detection and localisation of RP specimen pathology index tumour using ⁶⁸Ga-PSMA PET/CT or mpMRI. We defined tumour detection as imaging lesion corresponding with RP specimen tumour on any imaging plane, and localisation as imaging lesion matching RP specimen index tumour in all sagittal, axial, and coronal planes. Secondary outcomes included localisation of clinically significant and transition zone (TZ) index tumours. We defined clinically significant disease as GG 3–5. We used descriptive statistics and the Mann–Whitney U-test to define and compare demographic and pathological characteristics between detected, missed and localised tumours using either imaging modality. We used the McNemar test to compare detection and localisation rates using ⁶⁸Ga-PSMA PET/CT and mpMRI. Results: In all, 205 men were included in our analysis, including 133 with clinically significant disease. There was no significant difference between ⁶⁸Ga-PSMA PET/CT and mpMRI in the detection of any tumour (94% vs 95%, P > 0.9). There was also no significant difference between localisation of all index tumours (91% vs 89%, P = 0.47), clinically significant index tumours (96% vs 91%, P = 0.15) or TZ tumours (85% vs 80%, P > 0.9) using ⁶⁸Ga-PSMA PET/CT and mpMRI. Limitations include retrospective study design and non-central review of imaging and pathology. Conclusion: We found no significant difference in the detection or localisation of primary prostate cancer between ⁶⁸Ga-PSMA PET/CT and mpMRI. Further prospective studies are required to evaluate a combined PET/MRI model in minimising tumours missed by either modality.