Ionizing radiation has been shown to induce (cause) cancer in many different species of animals and in almost all parts of the body. It is one of the few scientifically proven carcinogens (cancer-causing agents) in human beings, although it appears to be a relatively weak carcinogen compared to many chemical agents. Many years may elapse between the radiation exposure and the appearance of the cancer.
The types of cancer that can be caused by radiation can also occur naturally (without increased exposure to radiation), but some occur more frequently as a result of radiation. For example, a higher percentage of small cell lung cancers occur in uranium miners as a result of exposure to alpha radiation (a form of highly ionizing radiation).
Organs differ in their sensitivity to the effects of radiation. The thyroid gland and bone marrow are most sensitive to radiation, while the kidney, bladder, and ovary seem to be least affected. Some forms of leukemia, a type of cancer that arises in the bone marrow, appear to be the most common radiation-induced cancers.
Evidence that ionizing radiation causes cancer comes from studies of atomic bomb survivors in Japan, persons exposed to large amounts of x-rays, and from certain occupational exposures, such as workers with lung exposure to alpha radiation. These studies, however, generally involved relatively high-dose exposure - greater than 10 centigray. (A centigray (cGy) is a standard unit of radiation dose.) Therefore, the risk estimates for lower doses of radiation have to be estimated from the high-dose data, and may not be accurate.
Dose-Related Radiation Effects
Ionizing radiation is probably the only carcinogen with evidence that its effects are related to dose exposure. The probability that cancer will result from radiation exposure increases as the dose increases. However, there is no evidence to suggest that the grade (tendency to grow and spread) of the resulting cancer is affected by the dose. In other words, higher doses of radiation do not cause more aggressive cancers.
Low-Dose Radiation Exposure
A number of studies over the past 20 years have looked at the impact of environmental radiation exposure in the dose range of 10 cGy or less. Careful analysis of this research revealed no significant increase in the incidence of all cancers combined, or of cancers in specific parts of the body. Research in this area is continuing.
Wednesday, February 4, 2009
Ionizing Radiation
Radiation can generally be defined as being ionizing or non-ionizing. Ionizing radiation consists of high-energy waves that are able to penetrate cells and can cause ionization in different parts of the cell. Ionization is the development of a positive charge in a molecule (group of atoms) that is normally neutral (without a charge). Ionized molecules are unstable and quickly undergo chemical changes. This can lead to the formation of free radicals that can damage the molecule or other molecules around it.
One type of molecule that is sensitive to ionizing radiation is DNA, the part of the cell that contains the genes (blueprints) for each person's characteristics. Ionizing radiation can lead to a mutation (change) in a cell's DNA, which could contribute to cancer, or to the death of the cell. All cells in the body can be damaged by ionizing radiation. The amount of damage is related to the dose of radiation received by the cell. While the process of cellular change from radiation takes only a fraction of a second, other changes such as the beginning of cancer may take years to develop.
Types of ionizing radiation include x-rays, gamma rays, cosmic rays, and particles given off by radioactive materials such as alpha particles, beta rays, and protons. These forms of radiation have different energy levels and can penetrate cells to different extents, but all are capable of causing ionization.
People may be exposed to 3 main types of ionizing radiation:
* Natural background radiation comes from cosmic rays from our solar system and radioactive elements normally present in the soil. This is the major contributor to worldwide radiation exposure.
* Non-medical synthetic radiation occurs as a result of above ground nuclear weapons testing that took place before 1962 as well as occupational and commercial sources.
* Medical radiation comes in the form of diagnostic x-rays and other tests, as well as from radiation therapy. Radiation therapy is currently used to treat some types of cancer and involves dosages many thousand times higher than those used in diagnostic x-rays.
One type of molecule that is sensitive to ionizing radiation is DNA, the part of the cell that contains the genes (blueprints) for each person's characteristics. Ionizing radiation can lead to a mutation (change) in a cell's DNA, which could contribute to cancer, or to the death of the cell. All cells in the body can be damaged by ionizing radiation. The amount of damage is related to the dose of radiation received by the cell. While the process of cellular change from radiation takes only a fraction of a second, other changes such as the beginning of cancer may take years to develop.
Types of ionizing radiation include x-rays, gamma rays, cosmic rays, and particles given off by radioactive materials such as alpha particles, beta rays, and protons. These forms of radiation have different energy levels and can penetrate cells to different extents, but all are capable of causing ionization.
People may be exposed to 3 main types of ionizing radiation:
* Natural background radiation comes from cosmic rays from our solar system and radioactive elements normally present in the soil. This is the major contributor to worldwide radiation exposure.
* Non-medical synthetic radiation occurs as a result of above ground nuclear weapons testing that took place before 1962 as well as occupational and commercial sources.
* Medical radiation comes in the form of diagnostic x-rays and other tests, as well as from radiation therapy. Radiation therapy is currently used to treat some types of cancer and involves dosages many thousand times higher than those used in diagnostic x-rays.
Radiation Exposure and Cancer
Radiation is the emission (sending out) of energy from any source. The light that comes from the sun is a source of radiation, as is the heat that is constantly coming off our bodies. When talking about radiation, however, most people think of specific kinds of radiation such as that produced by radioactive materials or nuclear reactions. Most forms of radiation have not been linked to cancer. Only high frequency radiation (ionizing radiation and ultraviolet radiation) has been proven to cause genetic damage, which can lead to cancer.
The hazards of exposure to some kinds of radiation were recognized shortly after the discovery of the x-ray in 1895. Skin reactions were observed in many people working with early x-ray generators, and by 1902 the first radiation-caused cancer was reported in a skin sore. Within a few years, a large number of such skin cancers had been observed. The first report of leukemia (a cancer of the bone marrow) in radiation workers appeared in 1911. Marie Curie, the discoverer of radium, and her daughter are believed to have died of radiation-caused leukemia. Since that time, many studies have confirmed the cancer-causing effects of some types of radiation.
The hazards of exposure to some kinds of radiation were recognized shortly after the discovery of the x-ray in 1895. Skin reactions were observed in many people working with early x-ray generators, and by 1902 the first radiation-caused cancer was reported in a skin sore. Within a few years, a large number of such skin cancers had been observed. The first report of leukemia (a cancer of the bone marrow) in radiation workers appeared in 1911. Marie Curie, the discoverer of radium, and her daughter are believed to have died of radiation-caused leukemia. Since that time, many studies have confirmed the cancer-causing effects of some types of radiation.
Subscribe to:
Posts (Atom)