Radiation thyroid gland exposure

To prevent radioactive iodides from lodging in the thyroid gland during exposure to excessive radiation, a potential appHcation of iodine acting as a thyroid-blocker has arisen. Eor this purpose potassium iodide was recommended (66). 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

Potassium iodine tablets can be used to reduce radioactive iodine exposure to the thyroid gland. According to the National Council of Radiation Protection and Measurement (NCRP), taking 130 milligrams of potassium iodine at or before exposure to radioactive iodine effectively blocks nearly 100% of radioactive iodine from reaching the thyroid.1 Waiting 4 hours after exposure to take potassium iodine... 

Holm, L.E., Eklund, G., and Limdell, G. (1980a). Incidence of malignant thyroid tumors in humans after exposure to diagnostic doses of iodine-131 II. Estimation of thyroid gland size, thyroid radiation dose, and predicted versus observed number of malignant thyroid tumors, J. Natl. Cancer Inst. 65,1221. 

The radiation exposure after the intravenous administration of " Tc-pertechnetate depends on the thyroid status, and whether a blocking agent has been administered. The thyroid gland, stomach wall, small intestine, upper and lower intestinal wall, and urinary bladder wall are the most exposed organs. 

In 1979 and 1986, nuclear accidents caused the release of radioactive iodine ( I) into the atmosphere (van Middleworth 1997, 2000). Ingestion of iodine in the form of potassium iodide can reduce the radiation dose to the thyroid gland by up to 90% if administered before or shortly after exposure (dosage 130 mg KI for adults). If administered 4 hours after exposure, KI blocks 50% of I uptake into the thyroid. 

Under most circumstances, there are no health hazards associated with potassium iodide. Taking an excess of the compound may have harmful effects on the thyroid gland, however. For that reason, people with an overactive thyroid should not take potassium iodide unless so directed by their doctors. Also, a person should not take potassium iodide as a preventative treatment against radiation. It provides no protection in advance of radiation exposure and, in excessive amounts, can create problems of its own for the thyroid. 

The thyroid gland is unique in its developmental sensitivity to malignancy following radiation exposure. Individuals older than 20 years of age do not have an increased risk of thyroid cancer when exposed to low-level thyroid irradiation (Boice, 2005, 2006 Ron et al., 1995). Yet, when individuals are less than 20 years of age at the time of low-level thyroid irradiation, the thyroid cancer risks increases (Boice, 2005, 2006 Ron et al., 1995). 

When administered as a major amount concentrates in the thyroid gland, although to a lesser extent in differentiated thyroid cancer compared with normal thyroid tissue. The short range of the emitted beta particles leads to cell damage and cell death. The emitted radiation, however, can be harmful to other organs of the patient and has the potential to induce cancer, especially with repeated treatments and high cumulative activities. Other people in the vicinity of the patient may be exposed to external radiation and contamination. For children, thyroid cancer after radiation exposure appears to be a significant risk, as has been documented after the accident in Chernobyl. 

KI only protects the thyroid gland and does not provide protection from any other radiation exposure. 

Potassium iodide, also called KI, only protects a person s thyroid gland from exposure to radioactive iodine. KI will not protect a person from other radioactive materials or protect other parts of the body from exposure to radiation. It must be taken prior to exposure (for example, if people hear that a radioactive cloud is coming their way) or immediately after exposure to be effective. Since there is no way to know at the time of an incident whether radioactive iodine was used in the explosive device, taking KI would probably not be beneficial.Also, KI can be dangerous to some people. Taking KI is not recommended unless there is a risk of exposure to radioactive iodine. 

In the second decade, the researehers were able to relate the growth retardation to lowered funetion of the thyroid. TTiyroid tumors, albeit nonmalignant, were widespread. Clearly thyroid function had been impaired by the ehildren s exposure to the penetrating radiation of fallout particles and the ingested radioiodine that accumulated in their developing thyroid glands. 

Radiation exposure has been associated with most forms of cancer in many organs, such as the lung, breast, and thyroid gland. If the cell is only modified by the radiation damage, the damage is usually repaired. In some conditions, the repair mechanism may not be perfect, and the modification will be transmitted to daughter cells. This may eventually lead to cancer in the tissue of the exposed individual. Radiation-induced cancer may manifest itself decades after the etqiosure and does not differ from cancers that arise spontaneously or are attributable to other factors. 

The Chernobyl nuclear accident in 1986 resulted in the largest radiation exposure in recent history. The radioactive materials released contained high levels of radioactive iodine (particularly, with a half-life of 8 days), an element that accumulates in the thyroid gland as a component of thyroid hormone. Following the explosion, people were exposed to deadly radioactive materials estimated to be 100 times greater than that associated with the detonation of the atomic bomb over Hiroshima. In Belarus, thyroid cancer in children under 18 increased from an incidence of 0.03-0.05 cases per 100,000 (1986-1988 data) to more than 10 times that level (5-8 cases per 100,000) in the period 1993-2002. Increases in thyroid cancer also were noted in Ukraine, with rates going from 0.02 per 100,000 (1986-1988 data) to 5-10 times that level (1-2.2 per 100,000) over the period from 1993-2002 (Reiners et al., 2013). There is little doubt that Chernobyl radiation exposure caused thyroid cancer among children in the affected area. 

Long-term health effects from exposure to low-to-moderate doses of radiation include cancer of the thyroid, prostate, kidney, liver, salivary glands, and lungs Hodgkin s disease leukemia and increased numbers of stillbirths and genetic defects. Concerns about potential long-term health effects often lead to anxiety and depression problems among those exposed to radiation. 

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