Value of PET/CT in thyroid carcinoma

FDG-PET is well established in the diagnostics of the three histologic main groups of thyroid cancer: anaplastic, medullary (MTC) and follicular cell derived (FTC) cancer. For each of the histologic groups a high accuracy is established for FDG-PET which can be increased by combining with a CT investigation. Moreover the intrinsically precise coregistration of PET and CT when using PET/CT enables the reliable coregistration of PET findings to morphology in the - often normal - CT image. Besides FDG-PET highly specific tracers (131I, 123I, 111In-Pentetreotide) are established in the diagnostics of thyroid cancer. Such tracers are also available with positron emitters, however not yet on a routine basis: 124I for FTC and 68Ga-DOTATOC mainly for MTC and oncocytic thyroid cancer. For such highly specific tracers coregistration and especially the hardware based coregistration is of special importance, as the images display considerably less anatomic information compared to e.g. the FDG image. Moreover, the precise coregistration is valuable when performing volumetry of lesions, what is essential for dosimetry of radioiodine or somatostatin-related radionuclide therapy. (orig.)