FLUORINE-18-FDG AND IODINE-131-IODIDE UPTAKE IN THYROID-CANCER

We conducted a prospective study to define the sensitivity of I-131 sc intigraphy and (18)FDG PET whole-body scanning in the detection of thy roid cancer and metastases. Methods: Forty-one patients with different iated thyroid carcinoma who underwent thyroidectomy and I-131 eliminat ion of the remaining thyroid were studied by (18)FDG whole-body PET in 52 examinations and by I-131 whole-body scanning. Results: Combined ( 18)FDG and I-131 imaging resulted in a senstivity of about 95%, with a lternating uptake of I-131 and (18)FDG in the metastases: I-131 trappi ng metastases with no (18)FDG uptake and (18)FDG trapping metastases w ith no I-131 uptake. Five uptake types were differentiated. Alternatin g uptake was found in about 90% of the patients, which was nearly iden tical to the sensitivity of the combined I-131/(18)FDG investigation. In six patients with increasing human thyroglobulin levels, we found t hat (18)FDG whole-body PET localized positive neck metastases of papil lary thyroid carcinomas that were histologically confirmed after extir pation. Conclusion: Combination (18)FDG and I-131 whole-body imaging p rotocol enables detection of local recurrence or metastases on whole-b ody scans that are often not shown by other imaging methods. Biochemic al grading of thyroid cancer may also be possible with this method: Tu mors with remaining functional differentiation for hormone synthesis a nd iodine uptake have low glucose metabolism in more than 95%; tumors without this functional differentiation of I-131 uptake show high gluc ose metabolism. Fluorine-18-FDG uptake seems to be an indicator of poo r functional differentiation, and possibly higher malignancy, in thyro id cancer.