ABSTRACT
Ionizing radiation is an established and well-quantified cancer risk factor, based on a large body of experimental and epidemiological studies. A history of exposure to ionizing radiation is an established human cancer risk factor in the sense that, for cancer sites making up the majority of the human cancer burden, there is solid scientific evidence of increased risk associated with high levels of exposure. Radiation dose, corresponding to the amount of energy absorbed per unit volume of tissue, is expressed in units of gray. Ionizing radiation is ubiquitous and cannot be avoided altogether, but exposure is to some extent controllable. Ionizing radiation is a proven and well-quantified cancer risk factor, but there is variation by organ site and histological subtype. The most thoroughly studied modifiers of radiation-related risk are factors that are almost always obtainable with information about exposure and disease incidence or mortality: sex, age at exposure, age at observation for risk, and time following exposure.
