Childhood Leukaemia and natural background radiation: Context and dosimetric aspects

摘要

Natural sources contribute the largest component of radiation dose to most members of the population. Can epidemiology detect the effect of these doses? Radon doses to the lung are generally much the largest to any organ or tissue from natural sources and a link between radon exposures and lung cancer is well established. Another possible group of diseases for study are childhood cancers, particularly leukaemia, which have relatively low incidence and are relatively easily induced by radiation. A number of such studies have been published. These were generally of ecological (geographical correlation) or case-control design. Ecological studies are potentially subject to confounding by effects that cannot be allowed for in the analysis. Conventional interview based case-control studies should be free of this problem but may be subject to participation or other biases and are very expensive if they are large enough to have the necessary power. Record-based case-control studies are able to overcome the latter problems. Natural background radiation comes largely from radionuclides in food, radon and thoron, terrestrial gamma rays and cosmic rays. Unfortunately it is very difficult to estimate individual doses from food. Radon and terrestrial gamma rays (with directly ionising cosmic rays) are the components commonly estimated for epidemiology. Organ doses from penetrating radiation, eg gamma rays, vary relatively little across the body. In contrast, doses from alpha-emitting radionuclides can be extremely sensitive to assumptions about the location of the sensitive cells in question and their separation from the sites of deposition of the radionuclide. Epidemiological studies can generally be conducted using only some quantity which is proportional to the organ doses (eg radon concentrations). However, even here organ dose estimates are required if the risk estimates from a study are to be compared with the literature or if power calculations are to be undertaken.