Non-131I-scintigraphy in the treatment and follow-up of thyroid cancer. Single-photon-emitters or FDG-PET?

With respect to further therapeutic options, whole-body 131I scintigraphy (WBS) is the most important functional imaging technique during treatment and follow-up of differentiated thyroid cancer. But in many patients, thyroid cancer tissue does not concentrate 131I and can therefore not be localized using WBS. In addition to morphologic techniques, which have a low specificity in many cases, other methods are necessary to localize tumor tissue in these patients. Besides 201Tl, which has been used initially as a tumor-seeking agent, sestamibi, tetrofosmin and 18F-DG for PET imaging have been evaluated in differentiated thyroid carcinoma. This paper summarizes the clinical impact of functional imaging with tracers besides 131I. In direct comparison, 18F-DG-PET has the highest sensitivity, which exceeds 80% in cases with negative WBS. If available, this method should be considered in all patients suffering from differentiated thyroid cancer with suspected recurrence and/or metastases, particularly in cases with elevated thyroglobulin values and negative WBS. But also 99mTc-labeled tracers can be used to detect tumor tissue with a sufficient sensitivity. In medullary thyroid cancer, which presents frequently with diagnostic difficulties, 111In-octreotide, 99mTc-(V)-DMSA, 131I/123I-mIBG, and anti-CEA can be used, in addition.