Prospective head-to-head comparison of ¹¹C-choline-PET/MR and ¹¹C-choline-PET/CT for restaging of biochemical recurrent prostate cancer

Whole-body integrated ¹¹C-choline PET/MR might provide advantages compared to ¹¹C-choline PET/CT for restaging of prostate cancer (PC) due to the high soft-tissue contrast and the use of multiparametric MRI, especially for detection of local recurrence and bone metastases. Ninety-four patients with recurrent PC underwent a single-injection/dual-imaging protocol with contrast-enhanced PET/CT followed by fully diagnostic PET/MR. Imaging datasets were read separately by two reader teams (team 1 and 2) assessing the presence of local recurrence, lymph node and bone metastases in predefined regions using a five-point scale. Detection rates were calculated. The diagnostic performance of PET/CT vs. PET/MR was compared using ROC analysis. Inter-observer and inter-modality variability, radiation exposure, and mean imaging time were evaluated. Clinical follow-up, imaging, and/or histopathology served as standard of reference (SOR). Seventy-five patients qualified for the final image analysis. A total of 188 regions were regarded as positive: local recurrence in 37 patients, 87 regions with lymph node metastases, and 64 regions with bone metastases. Mean detection rate between both readers teams for PET/MR was 84.7% compared to 77.3% for PET/CT (p > 0.05). Local recurrence was identified significantly more often in PET/MR compared to PET/CT by team 1. Lymph node and bone metastases were identified significantly more often in PET/CT compared to PET/MR by both teams. However, this difference was not present in the subgroup of patients with PSA values ≤2 ng/ml. Inter-modality and inter-observer agreement (K > 0.6) was moderate to substantial for nearly all categories. Mean reduction of radiation exposure for PET/MR compared to PET/CT was 79.7% (range, 72.6-86.2%). Mean imaging time for PET/CT was substantially lower (18.4 ± 0.7 min) compared to PET/MR (50.4 ± 7.9 min). ¹¹C-choline PET/MR is a robust imaging modality for restaging biochemical recurrent PC and interpretations between different readers are consistent. It provides a higher diagnostic value for detecting local recurrence compared to PET/CT with the advantage of substantial dose reduction. Drawbacks of PET/MR are a substantially longer imaging time and a slight inferiority in detecting bone and lymph node metastases in patients with PSA values >2 ng/ml. Thus, we suggest the use of ¹¹C-choline PET/MR especially for patients with low (≤2 ng/ml) PSA values, whereas PET/CT is preferable in the subgroup with higher PSA values. (orig.)