131IMIBG

131I-MIBG is a radiopharmaceutical that combines meta-iodobenzylguanidine labeled with the radioactive isotope iodine-131. It is used in nuclear medicine for both diagnostic imaging and targeted radiotherapy of certain adrenergic neuroendocrine tumors.

The agent is an analogue of norepinephrine and is taken up by the norepinephrine transporter into sympathetic nerve terminals and neuroendocrine tumor cells. After uptake, the iodine-131 emits gamma rays suitable for imaging and beta particles that deliver cytotoxic doses to tumor tissues. This dual emission enables both visualization of disease and selective destruction of tumor cells, while healthy tissues with low NET expression are less affected.

Clinical uses include diagnostic imaging to detect and stage neuroendocrine tumors such as pheochromocytoma, paraganglioma, and neuroblastoma, as well as to monitor response to therapy. Therapeutically, high-activity 131I-MIBG is used for patients with disseminated or high-volume disease, particularly relapsed or refractory neuroblastoma in children and metastatic pheochromocytoma or paraganglioma in adults. Imaging and therapy can be performed in the same clinical program, often in specialized nuclear medicine centers equipped for radiation safety and patient monitoring.

Administration is by intravenous infusion. Prior to treatment, thyroid blockade is given to minimize thyroid uptake of free radioiodine. Patients may require hospitalization or restricted activity due to radiopharmaceutical emissions, and hematologic monitoring is common because marrow suppression can occur. Side effects include nausea, hypertension-related symptoms, fatigue, and temporary cytopenias; thyroid, marrow, and other organ toxicity are considerations in patient selection and follow-up.

131I-MIBG remains an established option in select centers worldwide, with ongoing research exploring optimization, combination therapies, and alternatives for imaging and therapy.