A pheochromocytoma tumor is seen as a dark sphere in the center of the body (it is in the left adrenal gland). The image is by MIBG scintigraphy, showing the tumor by radiation from radioiodine in the MIBG. Two images are seen of the same patient from front and back. The image of the thyroid in the neck is due to unwanted uptake of radioiodine (as iodide) by the thyroid, after breakdown of the radioactive iodine-containing medication. Accumulation at the sides of the head is from salivary gland due to uptake of<unk>  mIBG by the sympathetic neuronal elements in the salivary glands. Meta-I-131iodobenzylguanidine is a radio-labeled analog of the adrenergic blocking agent guanethidine. Radioactivity is also seen from uptake by the liver, and excretion by the kidneys with accumulation in the bladder.<unk>  is used for unsealed source radiotherapy in nuclear medicine to treat several conditions. It can also be detected by gamma cameras for diagnostic imaging, however it is rarely administered for diagnostic purposes only, imaging will normally be done following a therapeutic dose. Use of the<unk>  as iodide salt exploits the mechanism of absorption of iodine by the normal cells of the thyroid gland. Treatment of thyrotoxicosis Major uses of<unk>  include the treatment of thyrotoxicosis (hyperthyroidism) due to Graves' disease, and sometimes hyperactive thyroid nodules (abnormally active thyroid tissue that is not malignant). The therapeutic use of radioiodine to treat hyperthyroidism from Graves' disease was first reported by Saul Hertz in 1941. The dose is typically administered orally (either as a liquid or capsule), in an outpatient setting, and is usually 400–600 megabecquerels (MBq). Radioactive iodine<unk>  alone can potentially worsen thyrotoxicosis in the first few days after treatment. One side effect of treatment is an initial period of a few days of increased hyperthyroid symptoms. This occurs because when the radioactive iodine destroys the thyroid cells, they can release thyroid hormone into the blood stream. For this reason, sometimes patients are pre-treated with thyrostatic medications such as methimazole, and/or they are given symptomatic treatment such as propranolol. Radioactive iodine treatment is contraindicated in breast-feeding and pregnancy Treatment of thyroid cancer<unk> , in higher doses than for thyrotoxicosis, is used for ablation of remnant thyroid tissue following a complete thyroidectomy to treat thyroid cancer. Administration of<unk>  for ablation Typical therapeutic doses of<unk>  are between 2220 and 7400 megabecquerels (MBq). Because of this high radioactivity and because the exposure of stomach tissue to beta radiation would be high near an undissolved capsule,<unk>  is sometimes administered to human patients in a small amount of liquid. Administration of this liquid form is usually by straw which is used to slowly and carefully suck up the liquid from a shielded container. For administration to animals (for example, cats with hyperthyroidism), for practical reasons the isotope must be administered by injection. European guidelines recommend administration of a capsule, due to "greater ease to the patient and the superior radiation protection for caregivers". Post-treatment isolation Ablation doses are usually administered on an inpatient basis, and IAEA International Basic Safety Standards recommend that patients are not discharged until the activity falls below 1100 MBq. ICRP advice states that "comforters and carers" of patients undergoing radionuclide therapy should be treated as members of the public for dose constraint purposes and any restrictions on the patient should be designed based on this principle. Patients receiving<unk>  radioiodine treatment may be warned not to have sexual intercourse for one month (or shorter, depending on dose given), and women told not to become pregnant for six months afterwards. "This is because a theoretical risk to a developing fetus exists, even though the amount of radioactivity retained may be small and there is no medical proof of an actual risk from radioiodine treatment. Such a precaution would essentially eliminate direct fetal exposure to radioactivity and markedly reduce the possibility of conception with sperm that might theoretically have been damaged by exposure to radioiodine." These guidelines vary from hospital to hospital and will depend on national legislation and guidance, as well as the dose of radiation given. Some also advise not to hug or hold children when the radiation is still high, and a one- or two- metre distance to others may be recommended.<unk>  will be eliminated from the body over the next several weeks after it is given. The majority of<unk>  will be eliminated from the human body in 3–5 days, through natural decay, and through excretion in sweat and urine. Smaller amounts will continue to be released over the next several weeks, as the body processes thyroid hormones created with the<unk> . For this reason, it is advised to regularly clean toilets, sinks, bed sheets and clothing used by the person who received the treatment. Patients may also be advised to wear slippers or socks at all times, and avoid prolonged close contact with others. This minimizes accidental exposure by family members, especially children. Use of a decontaminant specially made for radioactive iodine removal may be advised. The use of chlorine bleach solutions, or cleaners that contain chlorine bleach for cleanup, are not advised, since radioactive elemental iodine gas may be released. Airborne<unk>  may cause a greater risk of second-hand exposure, spreading contamination over a wide area. Patient is advised if possible to stay in a room with a bathroom connected to it to limit unintended exposure to family members. Many airports now have radiation detectors to detect the smuggling of radioactive materials. Patients should be warned that if they travel by air, they may trigger radiation detectors at airports up to 95 days after their treatment with<unk> . Other therapeutic uses The<unk>  isotope is also used as a radioactive label for certain radiopharmaceuticals that can be used for therapy, e.g.<unk> -metaiodobenzylguanidine <unk> -MIBG) for imaging and treating pheochromocytoma and neuroblastoma. In all of these therapeutic uses,<unk>  destroys tissue by short-range beta radiation. About 90% of its radiation damage to tissue is via beta radiation, and the rest occurs via its gamma radiation (at a longer distance from the radioisotope). It can be seen in diagnostic scans after its use as therapy, because<unk>  is also a gamma-emitter. Diagnostic uses Because of the carcinogenicity of its beta radiation in the thyroid in small doses,<unk>  is rarely used primarily or solely for diagnosis (although in the past this was more common due to this isotope's relative ease of production and low expense). Instead the more purely gamma-emitting radioiodine iodine-123 is used in diagnostic testing (nuclear medicine scan of the thyroid). The longer half-lived iodine-125 is also occasionally used when a longer half-life radioiodine is needed for diagnosis, and in brachytherapy treatment (isotope confined in small seed-like metal capsules), where the low-energy gamma radiation without a beta component makes iodine-125 useful. The other radioisotopes of iodine are never used in brachytherapy. The use of<unk>  as a medical isotope has been blamed for a routine shipment of biosolids being rejected from crossing the Canada—U.S. border. Such material can enter the sewers directly from the medical facilities, or by being excreted by patients after a treatment
Iodine-131
Iodine 
DOTA-TATE
Radium-223
Potassium iodide
Lugol's iodine
Strontium-90
Estramustine phosphate