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Erschienen in:
01.06.2013 | Original Article
Thyroglobulin levels and thyroglobulin doubling time independently predict a positive 18F-FDG PET/CT scan in patients with biochemical recurrence of differentiated thyroid carcinoma
Erschienen in: European Journal of Nuclear Medicine and Molecular Imaging | Ausgabe 6/2013
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Purpose
To assess the relationship between serum thyroglobulin (Tg) levels, Tg doubling time (Tg-DT) and the diagnostic performance of 18F-FDG PET/CT in detecting recurrences of 131I-negative differentiated thyroid carcinoma (DTC).
Methods
Included in the present study were 102 patients with DTC. All patients were treated by thyroid ablation (e.g. thyroidectomy and 131I), and underwent 18F-FDG PET/CT due to detectable Tg levels and negative conventional imaging. Consecutive serum Tg measurements performed before the 18F-FDG PET/CT examination were used for Tg-DT calculation. The 18F-FDG PET/CT results were assessed as true or false after histological and/or clinical follow-up.
Results
Serum Tg levels were higher in patients with a positive 18F-FDG PET/CT scan (median 6.7 ng/mL, range 0.7–73.6 ng/mL) than in patients with a negative scan (median 1.8 ng/mL, range 0.5–4.9 ng/mL; P < 0.001). In 43 (88 %) of 49 patients with a true-positive 18F-FDG PET/CT scan, the Tg levels were >5.5 ng/mL, and in 31 (74 %) of 42 patients with a true-negative 18F-FDG PET/CT scan, the Tg levels were ≤5.5 ng/mL. A Tg-DT of <1 year was found in 46 of 49 patients (94 %) with a true-positive 18F-FDG PET/CT scan, and 40 of 42 patients (95 %) with a true-negative scan had a stable or increased Tg-DT. Moreover, combining Tg levels and Tg-DT as selection criteria correctly distinguished between patients with a positive and a negative scan (P<0.0001).
Conclusion
The accuracy of 18F-FDG PET/CT significantly improves when the serum Tg level is above 5.5 ng/mL during levothyroxine treatment or when the Tg-DT is less than 1 year, independent of the absolute value.