What is Iodine 131?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 22 March 2020
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Iodine 131 is a radioactive iodine isotope produced in nuclear detonations or in controlled environments in nuclear reactors. This isotope poses a number of health risks, and it is also used in nuclear medicine, where it can be valuable when applied in an environment where appropriate monitoring is available. When iodine 131 is used in medical treatment, it is handled with care by authorized personnel only, in accordance with the law and policies at the facility where it is used.

In the human body, iodine accumulates in the thyroid gland. The thyroid actually needs small amounts of iodine to function normally, and in people who do not get enough iodine, a condition known as goiter can develop, and may be accompanied with cognitive disabilities. A buildup of iodine 131 in people who have been exposed to this element can damage thyroid cells, causing hypothyroidism. In the case of people exposed with fallout and nuclear accidents, this is not desirable; however, in medical treatment, controlled destruction of thyroid tissue may be desirable.


One use of this substance is as a tracer material in medical imaging studies. The patient is given a low dose and it is allowed to circulate through the body before a series of images are taken to identify thyroid cells, showing both the thyroid gland and any metastatic growths containing these cells in the case of a patient with thyroid cancer. In larger doses, this compound can be used in cancer treatment to ablate thyroid cells, killing a cancer.

Iodine 131 is expressed in the urine as the body breaks it down, and it has a half life of eight days, becoming harmless with time. Patients who receive therapeutic doses of iodine 131 may need to be isolated for safety, as the people around them can be in danger of radiation exposure. Once they are less radioactive, they can be released and allowed to recover at home. Because this compound can cause birth defects, patients are usually advised to avoid getting pregnant for at least six months after taking this drug.

Iodine 131 for medical use is manufactured in facilities that specialize in producing radioactive isotopes for nuclear medicine. Once it is made, it is placed in sealed containers for shipment to pharmacies equipped to handle radioactive materials. The pharmacy usually orders specific isotopes when it needs them for treatments to avoid having a backlog of radioactive isotopes waiting for use. When a patient is ready, the isotope is packaged and delivered to a nuclear medicine suite for use, under the supervision of a nuclear medicine specialist.


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Post 1

I would actually like to know what the careers of the people who use I-131 medically are called. No website so far that I have looked at has this information and this website would be a lot better if it did have that information.

Other than that the website was very helpful!

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