Radiation injury causes
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Causes
Exposure
External exposure
External exposure is exposure which occurs when the radioactive source (or other radiation source) is outside (and remains outside) the organism which is exposed. Below are a series of three examples of external exposure.
- A person who places a sealed radioactive source in their pocket
- A space traveller who is irradiated by cosmic rays
- A person who is treated for cancer by either teletherapy or brachytherapy. While in brachytherapy the source is inside the person it is still external exposure because the active part of the source never comes into direct contact with the biological tissues of the person.
One of the key points is that external exposure is often relatively easy to estimate, and if the irradiated objects do not become radioactive (except for a case where the radiation is an intense neutron beam which causes activation of the object'). It is possible for an object to be contaminated on the outer surfaces, assuming that no radioactivity enters the object it is still a case of external exposure and it is normally the case that decontamination is easy (wash the surface).
Internal exposure
Internal exposure is when the radioactive material enters the organism, and the radioactive atoms become incorporated into the organism. Below are a series of examples of internal exposure.
- The exposure due to Isotopes of potassium-40K (40K) present within a normal person.
- The exposure to the ingestion of a soluble radioactive substance, such as Strontium-90 (90Sr) in cow’s milk.
- A person who is being treated for cancer by means of an open source radiotherapy method where a radioisotope is used as a drug. A review of this topic was published in 1999.[1]
Because the radioactive material becomes intimately mixed with the affected object it is often difficult to decontaminate the object or person in a case where internal exposure is occurring. While some very insoluble materials such as fission products within a uranium dioxide matrix might never be able to truly become part of an organism, it is normal to consider such particles in the lungs as a form of internal contamination which results in internal exposure. The reasoning is that the particles have entered via an orifice and can not be removed with ease from what the lay person (non biologist) would regard as within the animal. It is important to note that strictly speaking the contents of the digestive tract and the air within the lungs are outside the body of a mammal.
Nuclear warfare
Nuclear warfare is made more complex by virtue of the fact that a person can be irradiated by at least three processes. The first (the major cause of burns) is not caused by ionizing radiation.
- Thermal burns from infrared heat radiation.
- Beta burns from shallow ionizing radiation (this would be from fallout particles, the largest particles in local fallout would be likely to have very high activities due to the fact that they would be deposited so soon after detonation and it is likely that one such particle upon the skin would be able to cause a localized burn), however these particles are very weakly penetrating and have a short range.
- Gamma burns from highly penetrating radiation, this would be likely to cause deep gamma penetration within the body which would result in uniform whole body irradiation rather than only a surface burn. In cases of whole body gamma irradiation (circa 10 Gy) due to accidents involving medical product irradiators some of the human subjects have developed injuries to their skin between the time of irradiation and death.
In the picture on the right the normal clothing that the woman was wearing would have been unable to attenuate the gamma radiation and it is likely that any such effect was evenly applied to her entire body. Beta burns would be likely all over the body due to contact with fallout, but thermal burns are often on one side of the body as heat radiation does not penetrate the human body. In addition, the pattern on her clothing has been burnt into the skin. This is due to the fact that white fabric reflects more infra-red light than dark fabric. As a result the skin close to dark fabric is burnt more than the skin covered by white clothing.
In addition, there is the risk of internal radiation poisoning by ingestion of fallout particles.
Radiation work e.g. industrial radiography
Radiation poisoning can result from accidental exposure to industrial radiation sources. People working with radioactive materials often wear dosimeters or film "badges" to monitor their total exposure to radiation. These devices are more useful than Geiger counters for determining biological effects, as they measure cumulative exposure over time, and are calibrated to change color or otherwise signal the user before exposure reaches unsafe levels. However, film badge types require the film to be developed, as with photographic film, and are used to measure long-term exposure where brief catastrophic exposures are not expected.
Nuclear reactor accidents
Radiation poisoning was a major concern after the Chernobyl reactor accident. It is important to note that in humans the acute effects were largely confined to the accident site. Thirty-one people died as an immediate result.
Of the 100 million curies (4 exabecquerels) of radioactive material, the short lived radioactive isotopes such as 131I Chernobyl released were initially the most dangerous. Due to their short half-lives of 5 and 8 days they have now decayed, leaving the more long-lived caesium-137 (137Cs (with a half-life of 30.07 years) and strontium-90 (90Sr (with a half-life of 28.78 years) as main dangers.
Other accidents
Improper handling of radioactive and nuclear materials lead to radiation release and radiation poisoning. The most serious of these, due to improper disposal of a medical device containing a radioactive source (teletherapy), occurred in Goiânia, Brazil in 1987. It is noteworthy that while the majority of accidents involve smaller industrial radioactive sources (typically used for radiography) a large number of the deaths which have occurred have been due to exposure to the larger sources used for medical purposes.
Ingestion and inhalation
When radioactive compounds enter the human body, the effects are different from those resulting from exposure to an external radiation source. Especially in the case of alpha radiation, which normally does not penetrate the skin, the exposure can be much more damaging after ingestion or inhalation. The radiation exposure is normally expressed as a committed effective dose equivalent (CEDE).
Deliberate poisoning
On November 23, 2006, Alexander Litvinenko died due to suspected deliberate poisoning with polonium-210. His is the first case of confirmed death due to such a cause, although it is also known that there have been other cases where radioactive thallium was used. In addition, an incident occurred in 1990 at Point Lepreau Nuclear Generating Station where several employees acquired small doses of radiation due to the contamination of water in the office watercooler with tritium contaminated heavy water.
References
- ↑ Wynn A. Volkert and Timothy J. Hoffman, Therapeutic Radiopharmaceuticals, Chemical Reviews 99(9) (1999); 2269–2292