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Treatment and Management

The major clinical concerns after significant I-131 exposure, especially in infants and children who are more susceptible than adults, include developing hypothyroidism and thyroid cancer. Currently, children who are born in the United States are screened at birth for thyroid function; therefore, no thyroid tests are necessary for children growing normally without other medical problems, unless they are exposed to significant doses of I-131.

Table. Summary of Initial and Follow-Up Visits for Patients Identified as Exposed to I‑131 in Previous Years

If a nodule is benign, the patient could be treated with T4 in a dose sufficient to suppress serum TSH, which will limit glandular growth. If the nodule decreases in size, the patient should be maintained on T4 indefinitely and the nodule monitored with palpation and ultrasound. If the nodule persists while the patient is on T4 therapy, a repeat FNAB is necessary. If the nodule grows during T4 therapy, surgical resection is indicated.

Distant metastasis is uncommon, but lung and bone are the most common sites. In the case of thyroid cancer that has metastasized to other organs, it is helpful to have additional pathology analysis to determine whether the cancer is a thyroid cancer or whether it originated from another organ. This is particularly important in the case of former nuclear workers who might be eligible for compensation only for cancer originating from certain organs, or for nonworkers who are seeking compensation through the legal system for exposure health outcomes.

• Most people affected by I-131 exposure are psychologically healthy, functioning adults who are experiencing high levels of stress.
• Accurate information on the possible health effects of I-131 is needed after exposures due to nuclear releases.

To work effectively with patients, physicians need to understand that people who have been exposed to radiation are having normal, typical emotional responses that are to be expected under the circumstances. After any exposure, it is important that the psychologic support for the patient be combined with a risk communication plan to provide accurate information about the acute and delayed health effects of I-131. This will give exposed persons some of the information they need to understand the event. To ensure that information is accurately and completely understood, it may need to be repeated over a period of days or weeks. Distribution of clearly written information, with references to the scientific literature, might also be useful. Provision of timely and correct information is one key to preventing stress and relieving psychosocial effects after notification of the potential health risks of I-131 exposure.

Persons exposed to I-131, as well as family members of those exposed, need an opportunity to ask questions of health experts about the potential risk for present or future effects. Psychologic support should be continued after the immediate event because fear of possible future health effects can persist and might contribute to psychologic illness.

Most people will suffer normal emotional distress; only a few will develop psychologic illnesses depending on the circumstances of their exposure. Specific psychotherapeutic or psychopharmacologic treatments might also be useful to treat posttraumatic stress disorders, anxiety disorders, or depression that might occur in some patients in the aftermath of exposure. However, if depression occurs in a patient exposed to I-131, it is important to differentiate organically based mood changes possibly related to hypothyroidism from psychologically based depression related to stress about the exposure. Depression is a disorder, but can be a symptom. Symptoms similar to depression, such as a sad mood, lethargy, and lack of appetite, can be caused by an underlying hypothyroid condition, which must be diagnosed and treated correctly and not mistaken for depression. Consultations between endocrinologists and psychiatrists are recommended for these complex situations.

To reduce internal exposure to I-131 by inhalation, residents of communities near a release could stay indoors with the doors and windows closed to keep contaminated air out of their homes. Moist towels can be laid on window sills and at the bottom of doors to reduce air infiltration. The exposure scenario determines the relative significance of the different pathways (Whicker and Pinder 2002).

• Prophylactic Administration of Stable Iodine (Potassium Iodide)
• Administration of potassium iodide (KI) can significantly reduce thyroid I-131 uptake.

Potassium iodide (KI) is the preferred form of stable iodine. Thyroid uptake of I-131 can be reduced by more than 90% through an immediate oral dose of KI. Failure to administer KI within 2–4 hours after exposure to I-131 eliminates protection against the risk for adverse health outcomes.

Taking KI just before or within 1 to 2 hours after exposure to I-131 can block more than 90% of the radioactive iodine uptake by the thyroid. This means that public health officials must notify the public and the health professional community of I-131 releases immediately. If KI is taken 3 hours after acute exposure, approximately 50% of the thyroid uptake of I-131 is blocked. When KI is taken 4 hours after acute exposure, only 10% of the I-131 thyroid uptake is blocked. Taking KI more than 4 hours after exposure provides little protection unless the exposure to I-131 continues. Contraindications include allergies to iodine and must be considered before administering KI. Potassium iodate (KIO3) can also be used, although it might be associated with slightly more gastrointestinal irritation. Information on age-specific dosage recommendations is given in the table below. Precautions and contraindications applicable to KI are found in Food and Drug Administration (FDA) guidelines (FDA 2001). To continue treatment, doses of KI should be administered once each day for 7 to 14 days to prevent recycling of the I-131 into the thyroid.

Table. Recommended Single Doses of Potassium Iodide (KI) as a Blocking Agent, by Age Group

Age Group	Fraction of Tablet
	130 milligram	65 milligram
Neonates (birth to 1 month)	1/8	1/4
Infants (1 months–3 years)	1/4	1/2
Children (3–12 years)	1/2	1
Adolescents and adults (12–40 years)	1	2
Adults over 40 years	0	0

For persons older than 40 years of age, the risk for radiation-induced thyroid cancer is extremely low, while the potential side effects of prophylaxis due to preexisting thyroid disease tend to increase. Adults over 40 therefore do not need to take potassium iodide as prophylaxis for exposure to I-131. In the United States, the FDA has recommended prophylaxis with stable iodine when the committed dose equivalent to the adult thyroid is expected to exceed 250 milliSieverts (mSv), the equivalent of 25 rem (Roentgen equivalent in man or mammal) (FDA 2001). Sale or use of KI for this purpose does not require a physician’s prescription.

Current Nuclear Regulatory Commission (NRC) policy acknowledges that the use of KI is a protective measure for specific local conditions for populations exposed to I-131. It also states that KI is an inexpensive and reasonable supplement to sheltering and evacuation in case of a nuclear release. NRC policy requires that consideration be given to the use of KI in developing site-specific emergency plans.

If you live within 50 miles of a nuclear facility (Emergency Planning Zones or EPZ) that produces or is capable of releasing I-131, you should work with your medical association, local or state public health department, emergency response organizations, and elected representatives to ensure that a stockpile of KI is available and a distribution plan is in place. Predistribution of sealed packets of KI tablets to residents within the EPZ, combined with educational materials, instructions, and engagement in exercises would enable a significant percentage of the at-risk population to efficiently undergo prophylaxis when so advised by public health officials. However, because predistribution is unlikely to completely reach the target or vulnerable population, supplemental stocks of KI tablets should be stored at strategic locations such as schools, hospitals, pharmacies, fire departments, and police stations. Individually sealed tablets of KI incorporated into a cardlike dose pack will be stable for 5–10 years, or possibly longer.

The conversion of contaminated milk to powdered milk, cheese, yogurt, or ice cream allows I-131 to decay to lower levels, thus reducing radiation exposure.

The easiest way to reduce or eliminate internal exposure to I-131 during a release is to find an alternate food source of items produced outside the contamination zone. Contaminated milk can be made into cheese, yogurt, or ice cream; it can also be converted to powdered milk that can be used after the I-131 decays away.

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Whicker FW, Pinder JE. 2002. Food chains and biogeochemical pathways. Health Phys 82(5):680–9.

Food and Drug Administration. 2001. Guidance: potassium iodide as a thyroid blocking agent in radiation emergencies. Rockville, MD: US Department of Health and Human Services.