Thyroid radiation exposure

After the nuclear explosion at Chernobyl in 1986, Anatoly and other professors and physicians created a foundation, For the Children of Chernobyl. Their goal was to send children abroad for the summers for a reprieve from radiation exposure which impairs their immune systems and has resulted in unprecedented levels of thyroid cancer in children and adults. The first host country to respond to their call for help was India. Before long, the foundation was sending 30,000 children every summer to host families and programs in many countries, including Germany, England, Japan, the U.S., Spain, Italy and France. 

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. 

Rubino, C., Cailleux, A., DeVathaire, R, Schlumberger, M. (2002). Thyroid cancer after radiation exposure. European Journal of Cancer, 38(5), 645-647. 

Within the following few weeks 28 of the 32 acute deaths of exposed employees were judged due to radiation exposure. Thyroid cancer in children under 18 rose from an incidence of 0.5 of 100,000 (1986-1988 baseline) to more than ten times that level (5-8 per 100,000) in Belarus (1993-2002). Increases were just as consistent, but of less magnitude for Ukraine, going from 0.2 per 100,000 from 1986 to 1988 (baseline) to 5-10 times that level (1 to 2.2 per 100,000) from 1993 to 2002. There is little doubt that Chernobyl radiation caused thyroid cancer. In 2,000 there were 4,000 cases of thyroid cancer in children under 18 drinking milk contaminated with in 2002 there were 12 deaths related to these exposures. 

Cancer is the major effect of low radiation doses expected from exposure to radioactive contamination. Laboratory studies have shown that a-, /S-, and y-radiation can produce cancer in virtually every tissue type and organ in animals that have been studied (ATSDR, 2001). Cancers observed in humans after exposure to radioactive contamination or ionizing radiation include cancers of the lungs, female breast, bone, thyroid, and skin. Different kinds of cancers have different latency periods leukemia can appear within 2yr after exposure, while cancers of the breast, lungs, stomach, and thyroid have latency periods greater than 20 yr. Besides cancer, there is little evidence of other human health effects from low-level radiation exposure (ATSDR, 2001 Harley, 2001). 

The situation in relation to thyroid effects is serious. Up to the end of 1995, there were more than 800 cases of thyroid cancer reported in children, mainly in Belarus. Thyroid cancer may be induced by causes other than radiation, but all these cases seem likely to be associated with radiation exposure due to the accident. They represent a dramatic increase in the normal incidence of this rare type of cancer and the increase seems not to persist among children born after 1986. Thyroid cancer is usually non-fatal with early diagnosis, treatment and attention. At the time of the Chernobyl Conference, three of the children affected had already died. The prospects cannot be precisely predicted the high incidence is expected to continue for some time and the number of reported cases may be in the thousands the mortality will depend very much on the quality and intensity of the treatment given to the affected children. 

There is no evidence to date of any increase in the incidence of any malignancies other than thyroid carcinoma or of any hereditary effects attributable to radiation exposure caused by the Chernobyl accident. This conclusion, surprising for some observers, is in accordance with the relatively small whole body doses incurred by the populations exposed to the radioactive material released. The lifetime doses expected to be incurred by these populations are also small. In fact, the risks of radiation-induced malignancies and hereditary effects are extremely small at low radiation doses and, as the normal incidences of these effects in people are relatively high, it is not surprising that no effects could be detected. 

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. 

Perhaps the best known use of potassium iodide today is as a treatment for radiation exposure. When a nuclear bomb explodes or a nuclear accident occurs, one of the most dangerous products released to the environment is a radioactive isotope known as iodine-131. Iodine-131 enters the human body and travels to the thyroid, where it attacks cells and tissues, eventually resulting in thyroid cancer. Experts recommend that people exposed to radiation take potassium iodide as a protection against this hazard. The potassium iodide saturates... 

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. 

Doses of 150pCi/g (5.5MBq/g) typically yield radiation doses of 12000cGy to the thyroid (Graham and Burman, 1986). Following treatment, radiation exposures to the stomach, marrow, liver and gonads are about 14, 6.8, 4.8 and 2.5 cGy per organ, respectively. The total... 

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). 

For children less than 5 years of age, we consider antithyroid medications as a first-line therapy. Radioactive iodine has also been successfully used in this age group without an apparent increase in cancer rates. Yet, it may be best to defer radioactive iodine therapy because of the possible increased risks of thyroid cancer after radiation exposure in very young children in the event that any thyroid tissue remains after radioactive iodine therapy, and to avoid the low level whole body irradiation associated with radioactive iodine. 

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. 

The maximal stimulation of uptake by thyroid tissue can be achieved by increasing serum TSH concentration above 25—30pU/ml. This can be achieved by thyroid hormone withdrawal, or by administration of recombinant human TSH (rhTSH), the latter enables sufficient iodine uptake while avoiding hypothyroidism and reducing total body radiation exposure (Pacini et al, 2006). 

Papillary thyroid carcinoma is a tumor of thyroid follicular epithelium with papillary and follicular growth pattern and the characteristic nuclear features. Papillary thyroid carcinoma makes about 70% of all thyroid carcinomas, often associated with radiation exposure or high iodine intake, and mainly metastasizes by invasion of lymph vessels. Papillary thyroid carcinoma frequently associated with different rearrangements mainly involving the RET/PTC gene discussed in a previous section. 

However, Aese indications for thyroid uptake have virtually disappeared, first because of the replacement of TSH stimulation test by sensitive TSH assays (H4, 18) and, second, by the replacement of tests of thyroid autonomy, such as the Ts suppression tests by TRH stimulation tests (see Section 5.3). This restricts the application of diyroid uptake tests mainly to a few special areas, particularly as a key test in the elucidation of patients with biosynthetic goiter. Many of these patients are children, and it is desirable to use in these as it has been shown that the radiation exposure from the standard dose of is approximately % of the exposure from the equivalait dose of (H18). Another advantage in using is that repeated studies in the one patient are possible, as its half-life is 2.2 hours compared with 8 days for I, and therefore there are no errors from residual activity from a previous dose. 

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

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 main diagnostic practices with radiopharmaceuticals are the procedures for bone, cardiovascular, lung perfusion, lung ventilation, thyroid scan, thyroid uptake, renal, liver/ spleen, and brain examinations. The effective doses per procedure are considerably higher and are 4.5 mSv, 8 mSv, 1.5 mSv, 1 mSv, 3.4 mSv, 15 mSv, 1.9 mSv, 1.7 mSv, and 6 mSv, respectively, and the number of procedures per 1,000 population are 4.5, 2.7, 1.8, 0.34, 4.1, 0.92, 0.89, 2.1, and 1.3, respectively for countries at health-care level I. But patients near to the end of their lives receive many of these exposures, and thus the doses are not distributed evenly among the population. Therefore, these doses should not be used for the assessment of detrimental effects of radiation exposure. 

There is a considerable latent period between radiation exposure and the appearance of cancer. For most cancers in adults, the latent period is at least 10 years, or even longer. The shortest latent period is for leukemia and thyroid cancer (3 to 5 years The appearance of radiation-induced cancers follows additive or multiplicative models of prediction with absolute or relative risks as main parameters. Assessment of the risk coefficients is based on the follow-up of exposed persons through epidemiological studies. 

The IAEA recognized that the number of deaths attributable to the Chernobyl accident has been of paramount interest to all concerned - the general public, scientists, the mass media, and pohticians. The IAEA noted that claims had been made that tens or even hundreds of thousands of persons have died as a result of the accident, and stated that these claims were exaggerated the total number of people that could have died or could die in the future due to Chernobyl-originated exposure over the lifetime of emergency workers and residents of most contaminated areas was estimated to be around 4000. This included some 50 emergency workers who died of acute radiation syndrome in 1986 and other causes in later years, 9 children who died of thyroid cancer, and an estimated 3940 people that could die from cancer contracted as a result of radiation exposure. 

A patient may be given radioactive tracers such as technetium-99m, iodine-131, gallium-67, and thallium-201 that emit gamma radiation, which is detected and used to develop an image of the kidneys or thyroid or to follow the blood flow in the heart muscle. Radiologists must be knowledgeable about radiation exposure to limit the amount of radiation to which patients are exposed. 

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