Radiation health effects
Radiation exposure can lead to either tissue reactions or stochastic effects (ICRP Publication 103, Annex A). Tissue reactions (ICRP Publication 118 CRP Statement on Tissue Reactions / Early and Late Effects of Radiation in Normal Tissues and Organs – Threshold Doses for Tissue Reactions in a Radiation Protection Context) can occur in the application of ionizing radiation in radiation therapy, and in interventional procedures, particularly when fluoroscopically guided interventional procedures are complex and require longer fluoroscopy time or acquisition of numerous images. Tissue reactions occur when many cells in an organ or tissue are killed, the effect will only be clinically observable if the radiation dose is above some threshold. The magnitude of this threshold will depend on the dose rate (i.e. dose per unit time) and linear energy transfer of the radiation, the organ or tissue irradiated, the volume of the irradiated part of the organ or tissue, and the clinical effect of interest.
Stochastic effect (somatic or heritable) increases with radiation dose and is probably proportional to dose at low doses and low dose rates (ICRP Publication 99 Low-dose Extrapolation of Radiation-related Cancer Risk). At higher doses and dose rates, the probability often increases with dose more markedly than simple proportion. At even higher doses, close to the thresholds of tissue reactions, the probability increases more slowly, and may begin to decrease as a result of the competing effect of cell killing. It is not feasible to determine on epidemiological grounds alone that there is, or is not, an increased risk of cancer for members of the public associated with absorbed doses of the order of 100 mGy or below. The linear non-threshold model remains a prudent basis for the practical purposes of radiological protection at low doses and low dose rates.