Positron Emission Tomography and Thyroid Cancer

Thyroid: nuclear medicine update

Nuclear medicine has been used in the evaluation and treatment of benign and malignant thyroid disease since the discovery of iodine 131 ((131)I) in the 1930s. Although traditional methods of imaging are routinely used, recent advancements such as SPECT/CT and PET/CT have greatly enhanced the ability of nuclear medicine to accurately detect and localize. Guidelines for the management of thyroid cancer continue to evolve, treatment regimens selected should balance the long-term risk of disease recurrence and cumulative risks of radiation exposure, and physicians should be aware of these updates and guidelines when caring for patients with thyroid disease.

PET and PET/CT in the management of thyroid cancer

The introduction of PET(-CT) has brought about a major paradigm shift in the management of thyroid carcinoma, especially from the diagnostic standpoint. From the viewpoint of patient management, the areas where it has made significant impact include the following: (1) the detection of disease focus in patients with differentiated thyroid carcinoma with elevated Tg levels and negative radioiodine scan. When localized disease is identified with F-18 FDG-PET-CT, surgery or focused radiotherapy could be utilized to eradicate the tumor; (2) the localization of disease in patients of MTC with elevated serum calcitonin levels; (3) the detection of unsuspected focal F-18 FDG uptake in the thyroid in patients undergoing whole body F-18 FDG PET for a different indication. This would prompt a workup to rule out thyroid carcinoma. The use of I-124 is evolving at this time and has been of great promise with regard to (a) its better efficacy of lesion detection and (b) the ability to provide lesion-specific dosimetry. In addition, F-18 FDG PET appears to be of potential value in patients with thyroid lymphoma in making the initial diagnosis, monitoring therapeutic response, and assessing for residual disease and/or recurrence.

Endocrine tumors: the evolving role of positron emission tomography in diagnosis and management

Endocrine tumors comprise a range of benign and malignant conditions that produce a spectrum of clinical symptoms and signs depending on the specific hormones they produce. The symptoms and presentations of these tumors are often independent of their size and location. Because of their expression of cell membrane receptors or production of specific types of hormones or peptides, endocrine tumors can be identified with functional radionuclide imaging much more readily compared to standard cross-sectional imaging. In recent years, 18F-fluoro-deoxy- D-glucose positron emission tomography (18F-FDG-PET) has emerged as a useful tool for diagnosing and assessing many tumors. In this review we describe how PET, using 18F-FDG and other radiopharmaceuticals can be useful in the diagnosis and management of a wide range of endocrine tumors.