ADVANCES IN PET - PART II 

The Quarterly Journal of Nuclear Medicine and Molecular Imaging 2008 March;52(1):2-8

Copyright © 2008 EDIZIONI MINERVA MEDICA

language: English, Italian

Fluorodeoxyglucose PET/CT in patients with differentiated thyroid cancer and elevated thyroglobulin after total thyroidectomy and 131I ablation

Salvatore B. ^{1, 2}, Paone G. ², Klain M. ², Storto G. ³, Nicolai E. ¹, D’Amico D. ¹, Della Morte A. M. ¹, Pace L. ^{2, 3}, Salvatore M. ^{2, 3}

¹ Fondazione SDN, Naples, Italy 2 Department of Biomorphological and Functional Sciences Federico II University, Naples, Italy 3 Institute of Biostructures and Bioimages National Council of Research, Naples, Italy

Aim. The aim of this study was to evaluate the role of 18F fluorodeoxyglucose-positron emission tomography (FDG-PET), differentiated thyroid cancer and thyroglobulin in patients with differentiated thyroid carcinoma (DTC) treated with therapeutic 131I because of elevated thyroglobulin (Tg) levels during follow-up. The results of FDG-PET/CT were compared with post-therapy 131I whole-body scan (131I-t-WBS) and Tg at short-term follow-up.
Methods. Forty-five patients with DTC underwent a new therapeutic 131I administration based upon Tg values >1.5 ng/mL. All patients underwent 131I-t-WBS 5-7 days after 131I therapy. A few days before 131I administration, a FDG-PET/CT scan was performed in all patients. FDG-PET/CT was considered positive (PET+) when at least one abnormal focus of FDG uptake was found; likewise, 131I-t-WBS was considered positive (WBS+) when at least one abnormal focus of uptake was found. Assessment of short-term response to radioiodine was performed by measuring Tg values.
Results. FDG-PET/CT was positive in 32 patients, 23 of which had a positive 131I-t-WBS, and negative in 13, 8 of which had a negative 131I-t-WBS. Overall agreement was 69%. Tg values were significantly higher in FDG-PET/CT positive (502±1 027 ng/mL) than in FDG-PET/CT negative patients (57±94 ng/mL). A significant difference emerged between 131I-t-WBS positive (561±1 086 ng/mL) and 131I-t-WBS negative (65±120 ng/mL) findings. In these 45 patients, Tg normalized in 36%, was reduced by at least 50% in 24%, and remained unchanged in the remaining 40%. Overall, at short-term follow-up, Tg values normalized in 77% of the 13 patients with negative FDG-PET/CT and in 19% of the 32 patients with positive FDG-PET/CT.
Conclusion. FDG-PET/CT is a powerful and useful tool for assessing patients with DTC. It can provide additional information in those patients with high Tg at follow-up and eligible for 131I therapy. A negative FDG-PET/CT could also represent a prognostic tool combined with serum Tg testing at short term follow-up.