NRC: Information for Patients Administered Radioactive Iodine (I-131)
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Information for Patients Administered Radioactive Iodine (I-131)

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Background

On April 28, 2014, in Staff Requirements Memorandum to COMAMM-14-0001/COMWDM-14-0001, the Commission, among other things, directed the NRC staff to develop a Web site that provides patients with information and links to relevant medical and patient advocacy Web sites about I-131 treatments.  NRC created this webpage to provide potential patients with information on radioactive iodide (RAI) treatment procedures so that patients will understand the reason for the procedures, the process, and how to reduce radiation exposure to others.

NOTE: If you have any questions about the information provided, you should speak with your phsyician about information that is specific to you.

NOTE: This site is for informational purposes only. The NRC is not endorsing or requiring the guidance in the following links.

NOTE: NRC is initially populating this Web site at the same time NRC is requesting information from the public in a Federal Register Notice titled "Patient Release Information Collection" on these and other topics that the patient and the medical community believe are important in understanding an I-131 medical procedure. NRC will be updating this webpage when that information becomes available.

Information

  • What is radioactivity?
  • Each element, such as iodine, is composed of a set number of electrons, protons, and neutrons that give it its chemical and physical characteristics. The number of neutrons in the nucleus may vary and provide a number of different iodine atoms that chemically act the same but have different physical properties. The nucleus may be stable or unstable. An unstable nucleus that spontaneously losses subatomic particles from its nucleus and emits energy in the form of radiation is considered radioactive. This loss of subatomic particles, such as beta particles (electrons), is called radioactive decay and there is a predictable time in which half of the unstable nucleuses will decay. This is called the physical half-life of the radioisotope.

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  • What is radioactive iodine (RAI)?
  • Two unstable forms of iodine, i.e., the radioactive isotopes I-123 (13 hour half-life and photon (x-ray) emitter is good for imaging the location of iodine in the body and harmless to thyroid cells) and I-131 (8 day half-life and both photon (gamma) and beta particle emitter can both image where iodine is in the body and destroy thyroid cells) are used in the diagnosis and treatment of thyroid disease. This radioactive iodine is used in the form of sodium iodide and because of the extremely small amounts used for imaging or destroying cells, RAI is safe to use in individuals who have had allergic reactions to seafood or X-ray contrast agents. RAI is given by mouth in pill or liquid form.

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  • RAI treatment (Includes: preparing for RAI treatment, what to expect before and after receiving the treatment, and side effects of RAI treatment)
  • Stable Iodine, an essential trace element, is used by the thyroid gland to produce two thyroid hormones (T3 and T4). In papillary and follicular thyroid cancers (differentiated thyroid cancer) and hyperthyroidism, the thyroid and cancer cells produce too much thyroid hormones. In these cases, radioactive I-131 can be used to replace stable iodine and kill both the normal and abnormal thyroid cells regardless of where they are located.

    Radioactive I-131 emits both gamma and beta radiation. The gamma radiation allows it to be easily detected and located with radiation survey meters and imaged by nuclear medicine imaging techniques. The gamma radiation from I-131 in the patients is the major source of external radiation to others after an I-131 procedure. The beta particles emitted are used to kill, destroy, or ablate cells that use iodine and makes it a good therapeutic agent. The beta radiation is the primary concern when there is an oral uptake of I-131 indirectly from contaminated surfaces or directly by transfer from the patient.

    For the radioactive iodine to be effective, the availability of stable iodine has to be reduced so more radioactive I-131 will be used by the cells.  Americans in major parts of the United States in the 1900's received too little iodine in their diets and suffered from a disease called hypothyroidism.  At that time a decision was made by public health officials to have iodine added to table salt (iodized salt) and other food staples to reduce the incidence of hypothyroidism.  One effect of this is that when thyroid cancer patients need to reduce the amount of stable iodine in their bodies before receiving radioactive I-131, they have to go on low iodine diets and avoid many foods.  A combination between a low iodine diet and increased thyroid stimulating hormone is used to increase the use of radioactive I-131 by the cells.

    The ThyCa: Thyroid Cancer: Survivors' Association, Inc. provides additional information on: Radioactive Iodine Ablation Treatment for Differentiated Thyroid Cancer; Preparation for RAI, including the Low-Iodine Diet; Raising Your TSH Level; What It May Feel Like To Be Hypothyroid During Withdrawal from Thyroid Hormone Replacement; Shortly Before You Receive Your RAI; After Your RAI – In Hospital or at Home; Your Home Dental Care after RAI; Post-Therapy Scan; Potential Side Effects of RAI Treatment.

    The ThyCa: Thyroid Cancer: Survivors' Association, Inc. provides additional information on low iodine diets in multiple languages.

    The ThyCa: Thyroid Cancer: Survivors' Association, Inc. provides additional information about the salivary gland side effect from I-131 treatment.

    The ATA: American Thyroid Association provides additional information on common questions and answers associated with the period after receiving radioactive iodine; Your Home Stay or Hospital/Home Stay; Information If You Go Home Immediately After Receiving RAI; What do I do at home? Information During Your Hospital Stay; How Long Will I Be in Isolation in the Hospital? What about Visitors? How Should I Communicate with my Nurse? What Should I Wear in the Hospital? What about Cleaning my Room? What about Cleaning my Room? How do I Order my Meals? What about my Medications. Can I still take them? Is there Anything Else I should Know? Radioactive Iodine Treatment - Side Effects; Signs to Watch for in Case of Drug Reaction (Allergy).

    The ATA: American Thyroid Association provides a brochure on frequently asked questions with radioactive iodine treatments.

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  • Basic radiation safety (includes: precautions to take after receiving treatment)
  • Radioactive I-131 emits both gamma and beta radiation and a person receiving an I-131 procedure will continue to emit both gamma and beta radiation until the I-131 is gone. The amount of I-131 will decrease over time as the unstable I-131 decays or as the body processes the iodine and eliminates the I-131 from the body. For hyperthyroid patients, the thyroid tissue uses and holds on to the radioactive I-131. Therefore, while the patient receives smaller doses than a thyroid carcinoma patient, the radioactive Iodine is retained longer by the person.

    Thyroid carcinoma patients, receiving radioactive I-131, have already had surgery to remove their thyroid gland but some "thyroid tissue" may remain. Therefore, they have less thyroid tissue to use the radioactive 1-131 and most of the radioactive I-131 remains in circulation as the body processes it and gets rid of it. It is processed by the parts of the body that produce fluids, such as the kidneys that produce urine, the sweat glands that produce sweat, and the salivary glands that produce saliva, and the mammary glands that produce milk if the person is lactating. Radioactive I-131 is also volatile so it may be released as a gas during normal breathing. If the person's kidney function is normal (and they are not lactating), removal of most of the free radioactive I-131 occurs within the first few days through the production of urine.

    Contamination of the area the patient is in can happen in a number of ways. Patients that vomit before the radioactive I-131 has been absorbed through the digestive track may lose a significant amount of the iodine they received in the vomited fluid. Their clothing and bed linens may become contaminated by sweat or other bodily fluids. Hands, coughing, or sneezing can contaminate objects in a room and normal room surfaces and trash. Saliva can contaminate eating utensils, partially eaten foods such a chicken, beef or pork bones and result in contaminated trash. Saliva and urine can cause contamination in bathrooms.

    Basic radiation safety associated with radioactive I-131 involves using the principles of time and distance to reduce exposure to others as the basis for precautions to take after treatment.

    The SNMMI: Society of Nuclear Medicine and Molecular Imaging provides general radiation information.

    The SNMMI: Society of Nuclear Medicine and Molecular Imaging provides guidelines and recommendations by Society of Nuclear Medicine and Molecular Imaging (SNMMI) to assist trained practitioners in evaluating patients for therapy with Iodine-131 (sodium iodide) for benign or malignant diseases of the thyroid gland. It provides precautions and responsibilities the patients, family members and caregivers, and medical practitioners should implement before and after therapy administration of RAI.

    As indicated in the previous section some of the questions and answers on the ThyCa: Thyroid Cancer Survivors' Association, Inc. also provide basic radiation safety information.

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  • Risks to others, to include risks to young children and pregnant women.
  • The risk to pregnant women is in the delivery of radioactive I-131 to the developing fetal thyroid. The risk to the lactating person is the increased radiation dose to breast tissue and transferal of radioactive iodine to the nursing infant.

    The risk to young children is both from their lack of understanding that they have to maintain a safe distance from an I-131 patient and their tendency to put fingers and things in their mouth that may be contaminated with I-131. Their thyroid glands are smaller and the same amount of radioactive will deliver a larger radiation dose to the child's thyroid than to an adult thyroid.

    The NRC's two Regulatory Issue Summaries (RIS) [RIS 2008-11, "Precautions to Protect Children Who May Come In Contact With Patients Released After Therapeutic Administration with Iodine-131." and RIS 2011-01, "NRC Policy on Release of Iodine-131 Therapy Patients under 10 CFR 35.75 to Locations other than Private Residences."] discuss the precautions that should be taken to protect infants, young children and pregnant females who may come in contact with patients released after administration of therapeutic amounts of iodine-131 (I-131).

    The RADAR - the RAdiation Dose Assessment Resource provides information by Society of Nuclear Medicine and Molecular Imaging (SNMMI) for special cases of dosimetry for the potentially pregnant patient, including dosimetry for hyperthyroid patients, athyreotic patients, and the unique case in which conception occurs some days or weeks after administration of I-131.

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Page Last Reviewed/Updated Friday, July 07, 2017