⁶⁸Ga-PSMA has been proposed as a promising imaging tracer for scanning prostate cancer patients and MR has shown high sensitivity and specificity for the detection of locoregional recurrences. The aim of this study was to evaluate the feasibility of 68Ga-PSMA evaluation with a PET/CT-MR system and to compare the detection rate of multiparametric MR versus ⁶⁸Ga-PSMA PET/CT for the identification of pelvic lesions in prostate cancer patients with biochemical recurrence. 

Patients with PSA relapse after treatment were included. We used a trimodality PET/CT-MR (3.0 T) setup using a dose of approximately 280 MBq of ⁶⁸Ga-PSMA. For MR an abbreviated protocol was planned with T1 and T2 sequences beginning at aortic bifurcation, high-resolution thin slices with T2 sequence at prostate loggia and focal DWI and ADC maps. MR images were performed during 30 minutes starting 30 minutes after tracer injection.

A total of 37 patients were enrolled of whom 25 (68%) had undergone radical prostatectomy and 12 treated with radiotherapy. The median PSA level was 3.5 ng/mL (0.2 to 138 ng/mL). Both techniques were positive in 20 patients (54%) and negative in 7 patients (19%). Eight patients were only positive with ⁶⁸Ga-PSMA alone (22%) and 2 with MR only (5%). In 11 patients (30%), PET/CT also showed metastatic lesions outside the pelvis. Local relapse was detected in 16 (43%) and 12 (32%) patients, pelvic bone metastases in 6 (16%) and 2 patients (5%), and pelvic lymph nodes in 11 (30%) and 3 (8%) patients, for PET/CT and MR, respectively. A statistically significant difference was only found for lymph node relapses (P=0.013). Furthermore, MR was very useful in patients with local recurrences detected in close proximity to the bladder.

⁶⁸Ga-PSMA PET/CT seems to be a better technique for the evaluation of pelvic lymph nodes. PET/CT-MR system is a feasible imaging modality.