Risk of childhood leukemia after low-level exposure to ionizing radiation

Leukemia risk models There is unambiguous epidemiological evidence that exposure to moderate and high doses of ionizing radiation increases the subsequent risk of leukemia [1,2]. This evidence is based upon studies of the Japanese survivors of the atomic bombings of Hiroshima and Nagasaki in 1945, and groups exposed therapeutically or occupationally. Models of radiation-induced leukemia risk derived from leukemia mortality among the Japanese atomic bomb survivors adopt a linear dose–response relationship in the low-dose (<100 mGy) region, and assume that there is no threshold dose below which there is an absence of risk [1,2]. The implication of these models is that even low doses of radiation increase the risk of leukemia to some (albeit small) extent. In the low-dose region, the excess relative risk (ERR) coefficient (the proportional increase in risk over background per unit radiation dose received by the red bone marrow) is predicted to increase after a minimum latent period of 2 years, and this increase is especially steep for those exposed as children, rising to a maximum of approximately 50 Gy some 7 years after exposure. The ERR then attenuates, so that, at 25 years after exposure, it is approximately 2, which is the proportional increase in risk experienced this long after exposure by those irradiated as adults [3,4]. Therefore, for those exposed as children, the proportional increase in the risk of leukemia is expressed over time as a distinct ‘wave’.