The Role of Nuclear Medicine in Imaging and Therapy of Neuroendocrine Tumors
Neuroendocrine tumors (NET’s) constitute a heterogeneous group of tumors characterized by the simultaneous expression of specific marker proteins and cell type-specific hormonal products. Metaiodobenzyluanidine (MIBG), labelled with 131I or 123I, and 111In-pentetreotide (Octreoscan) are the radiopharmaceuticals of choice in the current clinical practice. Positron emitting radiopharmaceuticals that are used in PET imaging are 18F-fluorodeoxyglucose (18F-FDG), 18F-fluorodopamine (18F-DOPA), 11C-hydroxy-tryptophan (11C-HTP), and Gallium-68 (68Ga-DOTATATE or DOTATOC). In diagnosis of gastroenteropancreatic neuroendocrine tumors (GEPs) Octreoscan is the preferred imaging method because of its high sensitivity. 131Ι/123Ι-MIBG scintigraphy is useful to characterize and locate intra-adrenal (pheochromocytomas) and extra-adrenal paragangliomas. Octreoscan has also high accuracy for extra-adrenal paragangliomas. 18F-FDG-PET or PET/CT seems to be useful in detecting the pheochromocytomas and GEPs that fail to concentrate MIBG and Octreocan. 123I-MIBG scintigraphy combined with urine analysis of catecholamine metabolites is the most sensitive indicator of neuroblastoma. In diagnosis of small cell lung cancer and pituitary adenomas Octreoscan has a high sensitivity. On the contrary, in medullary thyroid cancer the sensitivity of Octreoscan and 131Ι/123Ι-MIBG is low but sensitivity of 18F-FDG PET or PET/CT and 68Ga-DOTATATE and DOTATOC PET or PET/CT seems to be higher. With the introduction of 131I-MIBG and octreotide labelled with several radioisotopes, the field of treatment with radionuclides has been extended to a wide range of NETs. 111In-DTPA-Octreotide firstly was used in some clinical trials but recent advances in somatostatin analogues have paved the way to the development of octreotate, which can be labelled with both 177Lu and 90Y radionuclides.
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