Context. Patients with progressive MTC undergo multiple imaging procedures for diagnosis of relapse and staging.

Objective. To assess the sensitivity and prognostic value of ¹⁸F-FDG-PET/computed tomography (CT) and the imaging sensitivity of pre-targeted ¹³¹I-radioimmunotherapy (RIT) in patients with progressive MTC.

Design/Setting/Patients. We performed a prospective multicenter study in high-risk patients with rapidly progressing MTC enrolled in a phase-II pre-targeted RIT study, as documented by short serum calcitonin (Ct) or carcinoembryonic antigen (CEA) doubling time (DT).

Interventions/Main Outcome Measures. Patients underwent neck-thoracic-abdominal CT, spine and pelvic magnetic resonance imaging (MRI), whole-body post-RIT immunoscintigraphy (IS) with ¹³¹I, and whole-body ¹⁸F-FDG-PET/CT imaging. Imaging sensitivity and the correlation between FDG uptake and biomarkers DT were evaluated.

Results. Thirty-three patients with mean CEA and Ct DTs of 1.90 y (0.21 to 8.50) and 1.52 y (0.09 to 6.01), respectively, were evaluated. Sensitivity of FDG-PET/CT was 83% for neck, 85% for mediastinal, 75% for lung, 60% for liver, and 67% for bone metastases; overall sensitivity was 76%. Median standardized uptake value (SUVmax) was 5.23 (2.06 to 13.90). SUVmax correlated significantly with Ct DT (P=0.011) and with minimal DT (minimal value between CEA DT and Ct DT) (P=0.027). Overall sensitivity of post-RIT IS, CT, and bone magnetic resonance imaging (MRI) were 94%, 74% and 85%, respectively.

Conclusions. These results demonstrate the value of FDG-PET/CT for staging of patients with progressive MTC, especially in the neck and mediastinum, with possible prognostication by SUV quantification. Post-RIT IS was the most sensitive of the imaging modalities studied prospectively.