PET in Evaluation of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) are distinctive tumors which arise from cells which have neural and hormonal origins. The most common clinically-encountered NETs are gastroenteropancreatic tumors (GEP NETs), lung carcinoids, pheochromocytoma, and medullary thyroid carcinoma. Imaging plays a key role in the evaluation of these tumors including detection, staging, response assessment, and prognostication. Conventional imaging with computed tomography (CT) and magnetic resonance imaging (MRI) are still the first line imaging modalities used in the evaluation of these tumors. Radionuclide imaging of NETs is done with either planar imaging (with or without single photon emission computed tomography (SPECT)) or with positron emission tomography (PET). PET imaging offers many advantages over planar or SPECT imaging which includes better resolution, a better background-to-lesion ratio, and increased sensitivity. Fusion with CT greatly improves specificity and diagnostic confidence. Various PET tracers are available for evaluation of NETs of which F-18-fluorodeoxyglucose (F18 FDG), F-18-fluorolevodopa (F18 FDOPA), and Ga-68 somatostatin receptor (SST) imaging agents (e.g. DOTATATE, DOTATOC and DOTANOC) are currently the most widely used. In this brief review, we describe the role of these PET tracers in evaluation of NETs with an emphasis on (GEP NETs).