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131I-MIBG (Iodine-131 metaiodobenzylguanidine) is a radiopharmaceutical used primarily in the diagnosis and treatment of certain types of neuroendocrine tumors, including pheochromocytoma and neuroblastoma. It combines the radioactive isotope Iodine-131 with the molecule metaiodobenzylguanidine (MIBG), which is structurally similar to norepinephrine and is taken up by adrenergic tissue.

Mechanism of Action[edit | edit source]

131I-MIBG works by targeting adrenergic tissue, which is abundant in certain types of neuroendocrine tumors. Once administered, the MIBG component of the compound is selectively taken up by adrenergic cells. The radioactive iodine-131 then delivers targeted radiation to these cells, causing cellular damage and death. This makes 131I-MIBG useful both for imaging and for therapeutic purposes.

Diagnostic Use[edit | edit source]

In diagnostic applications, 131I-MIBG is used in scintigraphy to visualize tumors. The radiopharmaceutical is injected into the bloodstream, and its uptake by adrenergic tissue is detected using a gamma camera. This imaging technique helps in the localization and staging of neuroendocrine tumors.

Therapeutic Use[edit | edit source]

Therapeutically, 131I-MIBG is used to treat tumors that have been identified as MIBG-avid. The radiation emitted by iodine-131 helps to destroy cancerous cells while sparing most of the surrounding healthy tissue. This treatment is particularly useful for patients with metastatic or refractory neuroblastoma and pheochromocytoma.

Side Effects[edit | edit source]

Common side effects of 131I-MIBG therapy include nausea, vomiting, and a decrease in blood cell counts. More serious side effects can include thyroid dysfunction, bone marrow suppression, and secondary malignancies. Patients undergoing 131I-MIBG therapy are often given medications to protect the thyroid and to manage other side effects.

Preparation and Administration[edit | edit source]

131I-MIBG is prepared in specialized radiopharmacy facilities and must be handled with care due to its radioactive nature. The administration of 131I-MIBG is typically performed in a hospital setting, often in a specialized nuclear medicine or oncology department. Patients may need to stay in a radiation isolation room for a period following treatment to minimize radiation exposure to others.

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Contributors: Bonnu, Prab R. Tumpati, MD