Have raised cancer risks been seen at low radiation doses?
The most recent findings for the Japanese atomic bomb survivors indicate that cancer risks decrease with decreasing dose over a wide dose range. It is not possible to identify increased risks at very low doses, owing to limitations on the statistical precision at these levels. However, a recent analysis of cancer incidence has excluded the possibility that risks are increased only at doses exceeding 60 mSv. In general, the results from this study are consistent with there being no dose threshold for cancer risks. A pooled analysis of studies of thyroid cancer following external irradiation in childhood shows a linear trend in risk with dose, with raised risks identifiable down to about 100 mSv. Also, studies such as the Oxford Survey of Childhood Cancers have indicated a raised risk from prenatal x-ray exposures to the fetus of the order of 10-20 mSv.
