Molecular imaging in the management of thyroid cancer.

Thyroid cancer is the most common endocrine malignancy in adults. The disease is classified into papillary, follicular, medullary and anaplastic types, each with characteristic histology and patterns of biological behavior. Diagnosis of thyroid cancer is usually made by needle aspiration of suspicious thyroid nodules. Disease management of well-differentiated thyroid cancer relies upon characteristic accumulation of radioisotopes of iodine that continues to play a central role in detection and treatment of disease. Recombinant human thyrotropin (rhTSH) is used as an alternative to thyroid hormone withdrawal to provide TSH stimulation necessary for diagnostic radioiodine scintigraphy and preparation for thyroid remnant ablation and cancer therapy. Hybrid SPECT/CT cameras combining functional scintigraphic information with CT anatomy are replacing stand-alone gamma cameras and these devices have been shown to outperform traditional planar and SPECT imaging techniques. Similarly, clinical application of novel radioisotopes like [124I]iodine with PET/CT for thyroid cancer imaging provides improved lesion resolution and direct tumor dosimetry. Alternative tracers such as [18F]fluorodeoxyglucose (FDG) can be used to evaluate well-differentiated thyroid cancers that no longer express the Na+/I- symporter, with a role in staging Hürthle cell, poorly differentiated, and anaplastic thyroid cancers. Medullary thyroid cancer recurrences are often difficult to detect using conventional imaging and traditional radionuclide studies, whereas [18F]FDG and [18F]fluorodihydroxyphenylalanine (DOPA) PET and PET/CT show promise for localizing the often elusive source (s) of elevated calcitonin in these patients.