Deterministic Effects (Tissue Reactions) and Stochastic Effects
One of the characteristics of the deterministic effects (tissue reactions) is the existence of the threshold dose, which means that exposure to radiation under this level causes no effects but exposure to radiation above this level causes effects. Radiation exposure above the threshold dose causes deaths or degeneration of a large number of cells at one time and the incidence rate increases sharply.
On the other hand, in radiological protection, it is assumed that there is no threshold dose for stochastic effects. Under this assumption, the possibility that radiation exposure even at extremely low doses may exert some effects can never be eliminated. It is very difficult to epidemiologically detect stochastic effects due to radiation exposure at low doses below the range of 100 to 200 mSv, but the ICRP specifies the standards for radiological protection for low-dose exposures, assuming that effects would appear depending on dose levels (linear dose-response) (p.165 of Vol. 1, "Biological Aspect").
When assessing cancer risks due to low-dose exposures, results of the epidemiological studies of atomic bomb survivors in Hiroshima and Nagasaki have mainly been used (p.117 of Vol. 1, "Relationship between Solid Cancer Deaths and Doses"). It is known that cancer risks increase almost linearly as exposure doses increase above approx. 150 mSv. However, it is not clear whether risks also increase linearly in the case of radiation exposure at doses below 150 mSv. Additionally, experiments using animals or cultured cells have revealed that comparing high-dose exposures in a short time as experienced by atomic bomb survivors and low-dose exposures over a long period of time, the latter poses lower risks when the total exposure doses are the same (p.116 of Vol. 1, "Cancer-promoting Effects of Low-dose Exposures").
- Included in this reference material on March 31, 2013
- Updated on March 31, 2021