Radioactive iodine cancer

Th Toid cancers are often treated with radioactive iodine because the thyroid gland preferentially absorbs iodine. 

The nuclear explosions that devastated Hiroshima and Nagasaki killed 100,000 to 200,000 people instantaneously. Probably an equal number died later, victims of the radiation released in those explosions. Millions of people were exposed to the radioactivity released by the accident at the Chernobyl nuclear power plant. The full health effects of that accident may never be known, but 31 people died of radiation sickness within a few weeks of the accident, and more than 2000 people have developed thyroid cancer through exposure to radioactive iodine released in the accident. Even low levels of radiation can cause health problems. For this reason, workers in facilities that use radioisotopes monitor their exposure to radiation continually, and they must be rotated to other duties if their total exposure exceeds prescribed levels. 

Thyroid cancer Exogenous thyroid hormone may produce regression of metastases from follicular and papillary carcinoma of the thyroid and is used as ancillary therapy of these conditions with radioactive iodine. Larger doses than those used for replacement therapy are required. 

Therapeutic Techniques. Probably the most prominent therapeutic use of radiopharmaceuticals is radioactive iodine in the treatment of metastatic thyroid cancer. 131I has a half-life of about 8 days and emits gamma and beta rays. When iodine salts are taken into the body, most of the dose is concentrated in the thyroid gland. A dose of radioactive iodine salt similarly concentrates in the thyroid gland. When there is a cancer in the thyroid gland, or the gland is overactive (hyperthyroidism), the excessive... 

The anthropogenic radionuclides of most concern are those produced as fission products from nuclear weapons and nuclear reactors. The most devastating release from the latter source to date resulted from the April 26, 1986, explosion, partial meltdown of the reactor core, and breach of confinement structures by a power reactor at Chernobyl in the Ukraine. This disaster released 5 x 107 Ci of radionuclides from the site, which contaminated large areas of Soviet Ukraine and Byelorussia, as well as areas of Scandinavia, Italy, France, Poland, Turkey, and Greece. Radioactive fission products that are the same or similar to elements involved in life processes can be particularly hazardous. One of these is radioactive iodine, which tends to accumulate in the thyroid gland, which may develop cancer or otherwise be damaged as a result. Radioactive cesium exists as the Cs+ ion and is similar to sodium and potassium in its physiological behavior. Radioactive strontium forms the Sr2+ ion and substitutes for Ca2+, especially in bone. 

The neutral isotope of iodine is an essential element in the human body most of the iodine-127 is located in the thyroid gland. Iodine s radioactive isotope, iodine-131, is readily absorbed in the body, where it becomes concentrated in the thyroid gland and may produce cancers. Exposure to radioactive iodine is an increasing concern since it is produced by fission reactions in nuclear reactors and by nuclear weapons tests. 

Substances also may be attached covalently to proteins for transporting the substances to targets in the body. Examples of this approach have been transporting radioactive iodine or toxic substances attached to antibodies in attempts to kill cancer cells and attaching radioactive metals to proteins and bleomycin for similar purposes (122). A recent novel approach has been that of Wu and Means (123) who have attached insulin to artificially formed liposomes by a reductive alkylation modification. The insulin-liposome aggregate reacts with insulin receptors. 

Epidemiological studies of populations in the FSU exposed to fallout from the 1986 nuclear reactor explosion at Chernobyl and releases from the Chelyabinsk-65 complex demonstrate the health effects associated with exposure to radioactive iodine, strontium, and caesium. A study of 2.81 X 10" individuals exposed along the Techa River, downstream from Chelyabinsk-65, revealed that a statistically significant increase in leukemia mortality arose between 5 yr and 20 yr after the initial exposure (37 observed deaths versus 14-23 expected deaths see Cochran et al. (1993) and cited references and comments). There has been a significant increase of thyroid cancers among children in the areas contaminated by fallout from the Chernobyl explosion (Harley, 2001 UNSCEAR, 2000). The initial external exposures from Chernobyl were due to and short-lived isotopes. Subsequently, external exposures to Cs and nd internal... 

Almost all elements found in nature can now be made radioactive. Radioactive potassium and phosphorus are used as tracers to measure how effectively plants take up fertilizer from soil. Radioactive iodine is applied in nuclear medicine to diagnose and treat thyroid problems. Radiation treatment for cancer therapy uses radioactive cobalt, which is made by irradiating ordinary cobalt with neutrons. 

Baugnet-Mahieu L, Lemaire M, Laeonard ED, Laeonard A, and Gerber GB (1994) Chromosome aberrations after treatment with radioactive iodine for thyroid cancer. Radiation Research 140 429-431. 

RAMIREZ, M.J., SURRALLES, J., GALOFRE, P, CREUS, A., MARCOS, R., Radioactive iodine induces clastogenic and age-dependent aneugenic effects in lymphocytes of thyroid cancer patients as revealed by interphase FISH, Mutagenesis 12 (1997) 449-455. 

Some radioactive nuclides are especially damaging because they tend to concentrate in particular parts of the body. For example, because both strontium and calcium are alkaline earth metals in group 2 on the periodic table, they combine with other elements in similar ways. Therefore, if radioactive strontium-90 is ingested, it concentrates in the bones in substances that would normally contain calcium. This can lead to bone cancer or leukemia. For similar reasons, radioactive cesium-137 can enter the cells of the body in place of its fellow alkali metal potassium, leading to tissue damage. Non-radioactive iodine and radioactive iodine-131 are both absorbed by thyroid glands. Because iodine-131 is one of the radioactive nuclides produced in nuclear power plants, the... 

Radioactive iodine, a thyroid hormone antagonist, is used in hyperthyroidism and in thyroid cancer (see also Table 20). 

A considerable advance in the management of thyroid cancer has resulted from the introduction of recombinant human TSH (thyrogen). A dose of 0.9 mg is administered intramuscularly, followed by an identical dose 24 hours later. The serum thyroglobuLin is then measured 48-72 hours after the second TSH injection this has become the preferred diagnostic test for following patients with differentiated thyroid cancer who have had thyroidectomy and ablation of any remnant tissue with radioactive iodine. This regimen can also be used to stimulate iodine uptake by malignant cells in a total body scan (see below). 

F. Thyroid cancer after radioactive iodine fall-out ... 

Antithyroid drugs are preferred over radioactive iodine therapy by many clinicians based on the assumption that the risk of cancer is less after drug therapy than after radioactive iodine. However, data do not support this assumption. 

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 radioactive iodine is used, it is important that higher doses of be used in children. The goal of radioactive iodine therapy in children should be to ablate the thyroid gland and achieve hypothyroidism. If no thyroid tissue remains, the risk of thyroid cancer will be very small, if present at all. To achieve this goal, we now use doses of I of 200—300 p,Ci/g of thyroid tissue. 

When used at doses that defiver 150 Gy or more (<150p,Gi I/g of thyroid tissue), radioactive iodine is an effective cure for Graves disease and is associated with few acute side-effects. Potential long-term adverse side-effects, including thyroid cancer and genetic damage, have yet to be observed in individuals treated as children or adolescents with 1. 

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