Comparison of 68Ga-prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) and multi-parametric magnetic resonance imaging (MRI) in the evaluation of tumor extension of primary prostate cancer

Background: To compare the diagnostic performance of Ga-68-prostate-specific membrane antigen positron emission tomography/computed tomography (Ga-68-PSMA PET/CT) with multi-parametric magnetic resonance imaging (mpMRI) on extracapsular extension (ECE) and seminal vesicle invasion (SVI) in primary prostate cancer and its impact on therapeutic decisions. Methods: We retrospectively enrolled 54 patients with both PET/CT and mpMRI before radical prostatectomy. Diagnostic performance of mpMRI, PET/CT and their combination (com-MRI/PET) on ECE and SVI on a patient basis were analyzed. The impact of additional PET/CT scanning on therapeutic decisions were presented. Results: Among the 54 patients, 17 had tumor limited in the prostate gland, 25 only had ECE and 12 patients had both SVI and ECE on pathology. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of ECE were 54%, 94%, 95%, 48% on mpMRI, 78%, 94%, 97%, 67% on PET/CT and 83%, 88%, 94%, 71% on com-MRI/PET. Both PET/CT and com-MRI/PET had a higher sensitivity than mpMRI on ECE diagnosis (78% vs. 54%, P<0.05 and 83% vs. 54%, P<0.05). No difference was observed between PET/CT and com-MRI/PET (78% vs. 83%, P=0.17). The Sensitivity, specificity, PPV and NPV of SVI were 67%, 93%, 72%, 91% on mpMRI, 75%, 95%, 82%, 93% on PET/CT and 75%, 88%, 64%, 93% on com-MRI/PET. No difference was found between the three scannings. After the additional evaluation of PET/CT, 18.5% (10/54) turned from nerve-sparing surgery to non-nerve sparing surgery. Conclusions: Ga-68-PSMA PET/CT has a higher sensitivity on ECE detection than mpMRI but shows no superiority on SVI.