A41 Deterministic effects

Radiation may kill cells of a tissue/organ. If the numbers of cells killed is low, the tissue keeps on functioning without any serious consequence. If the number of cells killed increases, the tissue is harmed and loses its function, and eventually the tissue or even the organ itself may die. It is clear that an increasing number of dead cells causes more and more serious damage to the tissue. This depends on the fact that cell depletion is a dynamic process in competition with proliferation of unaffected cells. If the loss of cell is low it can be quickly compensated by repopulation (no damage or short time effects); if the loss is large there is a drastic non-compensated reduction of tissue cells (serious damage and/or death). The proportion of cells killed depend on dose, therefore the severity of effects depends on dose as well. These effects are defined as deterministic and have dose thresholds.

Some deterministic effects are: temporary or permanent sterility, depression of the blood-forming system, skin reddening, desquamation, skin loss, lens inflammation, cataract. A peculiar case of deterministic effect is the radiation syndrome from acute and whole body irradiation. If the dose is high enough, the strong cell depletion in vital organs (blood-forming organs, gastro-intestinal tract etc.) causes death. An acute whole body exposure dose ¿etwee« 3 5 Gy, without any specific medical treatment, causes the death of 50% of the population exposed.

Figure A.4 gives some thresholds for deterministic effects are shown. The thresholds, like all thresholds for deterministic effects, apply to people in normal health [UNSCEAR, 1993].

Deterministic effect Threshold, Gy

Male temporary sterility

Deterministic effect Threshold, Gy

Male temporary sterility

acute exposure

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