11C-Methionin (MET) PET vs 18F-FDG PET in the follow-up of differentiated thyroid cancer.

Although FDG PET(/CT), under TSH stimulation, is now considered as a valuable, established diagnostic imaging tool in the follow-up of 131I-negative patients for the detection of recurrences or metastases, the interest for new tracers and improvement of diagnostic tools in thyroid cancer is growing. Another target for metabolic tumor imaging is the increased protein metabolism and transport in cancer cells, to which radiolabeled amino acids can be applied. Amino acid transport is generally increased in malignant tissue, which could be associated with specific cell surface changes in transformed cells. The process of malignant transformation requires in general that cells acquire and use nutrients efficiently for energy, protein synthesis and cell division. Two major steps are involved in protein metabolism including increased amino acid transport and protein synthesis. It is imaginable that thyroid cancer could sufficiently concentrate amino acids due to its protein synthesis (e.g. thyroglobulin) and the often slowly progressive character in the well-differentiated tumors (e.g. Hurthlecell carcinoma).


The general feasibility of amino acid imaging with C-11 methionine (MET) PET under TSH suppression in differentiated thyroid cancer (DTC) has been shown (Phan et al, in press NMC). Interesting finding in the study of Phan et al. was the complementary uptake of MET and FDG in 25% of the patients. It has been hypothesized that this finding might be explained by the degree of tissue dedifferentiation. Hürthlecell carcinoma are known to be less radioiodine-avid compared to the well-differentiated papillary and follicular carcinoma or can be even non-iodine or non-FDG avid. For this group of patients MET PET might be of complementary value.


In-vitro study in the rat thyroid cells has suggested that the TSH level does not influence the amino acid uptake. However, no clinical intra-individually comparative studies between 18F-FDG PET and 11C-MET PET during (rh)TSH stimulation are available. It would be of interest to evaluate the diagnostic yield of MET PET scans under (recombinant human, rh)TSH stimulation and to compare these results with TSH stimulated FDG PET.

1. To evaluate the clinical performance of MET PET during rhTSH stimulation and to compare the results of the rhTSH stimulated MET PET with the standard rhTSH stimulated FDG PET in patients with negative post-treatment 131-I scans and elevated serum thyroglobulin (Tg);

2. To evaluate the (complementary) value of MET PET in patients with persistent or recurrent Hürthlecell carcinoma in the post-ablation phase and during follow-up.

No additional time point. 11C-MET PET scan will be combined with 18 FDG PET scan.

11C-MET PET scan.