Ga-PSMA and C-Choline comparison using a tri-modality PET/CT-MRI (3.0 T) system with a dedicated shuttle.

Background: The aim of this study was to prospectively compare the detection rate of Ga-PSMA versus C-Choline in men with prostate cancer with biochemical recurrence and to demonstrate the added value of a tri-modality PET/CT-MRI system.

Methods: We analysed 36 patients who underwent both C-Choline PET/CT and Ga-PSMA PET/CT scanning within a time window of 1-2 weeks. Additionally, for the Ga-PSMA scan, we used a PET/CT-MRI (3.0 T) system with a dedicated shuttle, acquiring MRI images of the pelvis.

Results: Both scans were positive in 18 patients (50%) and negative in 8 patients (22%). Nine patients were positive with Ga-PSMA alone (25%) and one with C-Choline only (3%). The median detected lesion per patient was 2 for Ga-PSMA (range 0-93) and 1 for C-Choline (range 0-57). Tumour to background ratios in all concordant lesions ( = 96) were higher for Ga-PSMA than for C-Choline (110.3 ± 107.8 and 27.5 ± 17.1, mean ± S.D., for each tracer, respectively  = 0.0001). The number of detected lesions per patient was higher for C-Choline in those with PSA ≥ 3.3 ng/mL, while the number of detected lesions was independent of PSA levels for Ga-PSMA using the same PSA cut-off value. Metastatic pelvic lesions were found in 25 patients (69%) with Ga-PSMA PET/CT, in 18 (50%) with C-Choline PET/CT and in 21 (58%) with MRI (3.0 T). MRI was very useful in detecting recurrence in cases classified as indeterminate by means of PET/CT alone at prostate bed.

Conclusions: In patients with prostate cancer with biochemical recurrence Ga-PSMA detected more lesions per patient than C-Choline, regardless of PSA levels. PET/CT-MRI (3.0 T) system is a feasible imaging modality that potentially adds useful relevant information with increased accuracy of diagnosis.