Sunday, December 27, 2009

Radiation health effects : Deterministic effects

1- Deterministic effects

A very high dose to the whole body can cause death within weeks. For example, an absorbed dose of 5 gray or more received instantaneously would probably be lethal, unless treatments were given, because of damage to the bone marrow and the gastro­intestinal tract. Appropriate medical treatment may save the life of a person exposed to 5 gray, but a whole body dose of, say, 50 gray would almost certainly be fatal even with medical attention. A very high dose to a limited area of the body might not prove fatal, but other early effects could occur. For example, an instantaneous absorbed dose of 5 gray to the skin would probably cause erythema - painful reddening of the skin - within a week or so, whereas a similar dose to the reproductive organs might cause sterility.

These types of effect are called deterministic effects: they occur only if the dose or dose rate is greater than some threshold value, and the effect occurs earlier and is more severe as the dose and dose rate increase. Deterministic effects in an individual can be identified clinically to be the result of radiation exposure .

One type of deterministic effects occurs a longer time after exposure. Such effects are not usually fatal, but can be disabling or distressing because the function of some parts of the body may be impaired or other non-malignant changes may arise. The best-known examples are cataracts (opacity in the lens of the eye) and skin damage (thinning and ulceration). High absorbed doses of several gray are normally required to induce these conditions.

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