Adequate Diagnostic Performance of Combined [¹⁸F]-Fluormethylcholine PET-CT with Diffusion-Weighted MRI in Primary Staging of High Risk Prostate Cancer

Introduction: [¹⁸F]-fluoro-methylcholine (FCH) PET/CT and MRI with diffusion-weighted MRI (DW-MRI) have insufficient performance in lymph node staging of primary prostate cancer by themselves, but the combination may perform better. We aim to prospectively determine the diagnostic performance of combined FCH PET and MRI for lymph node staging. Methods: This was a single site study of diagnostic accuracy in a well-defined group of 21 consecutive high-risk primary prostate cancer patients (>30% chance of lymph node metastases) in a large community hospital. We performed FCH PET/CT and MRI with DW-MRI prior to endoscopic extended pelvic lymph node dissection (EPLND). PET was fused and interpreted together with various MRI image sets (T1, T2, DWIBS) and was only scored positive when a lymph node seen on MRI coincided with increased focal FCH uptake on PET. Findings were compared with detailed histological evaluation, on a per-patient and per-region level. We calculated sensitivity, specificity, positive and negative predictive value of combined PET-MRI. Results: 14 out of 21 patients had metastatic lymph nodes with 37 out of 164 evaluable regions harboring metastases. On a per-patient analysis, PET-MRI had a sensitivity/specificity of 79/100% with a PPV/NPV of 100/77%. On a per-region analysis (n = 164) these figure were 65/99% and 96/91%, respectively. Conclusions: Combined DW-MRI and FCH PET/CT has a very high positive predictive value in high risk prostate cancer patients. If confirmed in larger series a positive combined scan may safely allow cancellation of surgical staging in selected patients, depending on local protocols in N1 M0 patients.