Does addition of multiparametric MRI to PSMA PET/CT improve diagnostic accuracy for biochemical recurrence after radical prostatectomy?

Objectives To analyse the utility of adding multiparametric magnetic resonance imaging (mpMRI) with 68 Ga‐prostate‐specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) in detection of local recurrence (LR) and distant recurrence (DR) in patients with biochemical recurrence (BCR), by describing detection rates over time since radical prostatectomy (RP), describing detection rates at differing prostate‐specific antigen (PSA) intervals, and identifying clinicopathological factors that predict detection of recurrence on imaging. Patients and Methods Patients with BCR after RP were identified from 2016 to 2020. Kaplan–Meier analysis was performed for LR and DR on mpMRI, 68 Ga‐PSMA PET/CT, and paired/combined scans, and multivariate regression was performed identifying predictors of LR and DR. Results A total of 117 patients underwent 150 sets of paired scans for BCR after RP, at PSA thresholds 0.2, 0.5, and 1.0 ng/mL. The 68 Ga‐PSMA PET/CT had higher detection rates of DR at PSA levels of <0.2, 0.2–0.5, 0.5–1.0, and >1.0 ng/mL vs mpMRI (6.1%, 10%, 25% and 36% vs 3%, 6.7%, 6.3%, and 24%, respectively). Meanwhile, mpMRI had higher detection rate of LR than 68 Ga‐PSMA PET/CT (30.3%, 33.3%, 40.6%, and 40% vs 0%, 13.3%, 18.8%, and 32%, respectively). The detection rate for LR was significantly higher on MRI compared to PSMA at PSA levels of <0.2 and 0.2–0.5 ng/mL ( P < 0.001 and P = 0.001, respectively). The detection rate for DR was significantly higher on PSMA than MRI at PSA levels of 0.5–1.0 ng/mL ( P = 0.039). On multivariate analysis, PSA velocity was a statistically significant predictor of both LR and DR on MRI alone, PSMA alone, and combined results of paired PSMA and MRI, and International Society of Urological Pathology grade was a statistically significant predictor of DR on MRI. Conclusion The mpMRI had a higher detection rate for LR, while 68 Ga‐PSMA PET/CT had a higher detection rate for DR. PSA velocity was a significant predictor of both LR and DR on both imaging modalities. In BCR after RP, addition of mpMRI with 68 Ga‐PSMA PET/CT may improve diagnosis of recurrent lesions and patient selection for treatment.