Comparison of C-11-methionine PET and F-18-fluorodeoxyglucose PET in differentiated thyroid cancer

Background The purpose of this prospective study is to evaluate the possibility of C-11-methionine (Met) PET compared with F-18-fluorodeoxyglucose (FDG) PET for the detection of recurrent or metastatic disease in patients with differentiated thyroid cancer (DTC).Materials and methods Twenty patients with clinical suspicion of recurrent DTC but negative posttreatment I-131-whole body scans were included in the study. Both C-11-Met PET and F-18+DG PET were performed within 1 week. PET images were analyzed by two independent and blinded physicians using visual and standardized uptake value analysis. PET results were also correlated with radiologic and/or cytological investigations.Results Thirteen patients showed concordant findings on both PET scans: six patients showed uptake and in seven no uptake was observed. In six of the seven patients without Met and FDG uptake, additional MRI and ultrasound-guided fine needle aspiration cytology of the lymph nodes revealed inconclusive or negative results. Six patients showed discordant findings on the PET scans: in three patients uptake was only observed on the Met PET, confirmed by MRI in one. In three patients lesions were seen on the FDG PET, confirmed by computed tomography or ultrasound-guided fine needle aspiration cytology. However, those lesions were not compatible with the lesions seen on the Met PET. In general, FDG uptake appeared to be higher than Met uptake, but was not significant (P=0.075).Conclusion This study shows that imaging using radiolabeled amino acids is feasible in DTC. For now, C-11-Met PET has not proven to be superior to F-18-FDG PET in the detection of recurrent disease in DTC. Complementary uptake of Met and FDG has, however, been observed, which has to be further clarified and long-term follow-up is needed to define the true clinical value of the C-11-Met PET, and possible other amino acids tracers.