The Estimation of Cancer Risk at Low Doses

The cancer-causing effects of ionising radiation at high doses have been known for many decades. Since then, there have been many large studies worldwide of cancer arising in people exposed to high and low doses. These studies include people exposed to the atomic bomb explosions in Japan, to fallout from nuclear weapons tests and during radiation accidents. Information is also available from people irradiated for medical reasons, during their work or as a result of living in a region that has unusually high levels of radioactive radon gas or gamma radiation. From all of this scientific work published in peer-reviewed papers we know more about cancer risk after ionising radiation than for any other cancer-causing substance. However, because cancer is unfortunately a common disease with many causes it is extremely difficult to measure directly the small extra risk from ionising radiation when the doses are very low. National and international organisations worldwide constantly discuss the best way to use the cancer information that we have to make estimates of the risks at the low doses that are received by the general public and workers. Special attention is given to the risks from man-made ionising radiation that can be controlled and regulated. As mentioned earlier, it is also important to take account of the risks from natural radiation, most of which cannot be controlled.

At present the estimate of cancer risk at low doses as recommended by NRPB for use in the UK predicts that a lifetime of exposure of the population to all sources of ionising radiation (natural plus man-made) could be responsible for an additional risk of fatal cancer of about 1% - this can be compared with a life-time risk of cancer of about 20-25% from all causes. The very small doses from non-medical, man-made radiation would be responsible for only a tiny fraction (about one-hundreth) of this 1% radiation risk. Therefore, compared with other known cancer risk factors in the population such as cigarette smoking, excessive exposure to sunlight and poor diet, the risk to the population from non-medical man-made radiation is generally agreed to be very small indeed.

It was the responsibility of NRPB, now the HPA, to advise the UK Government on cancer risk estimates and standards for radiation protection. At present there are only small differences in the risk estimates used by different countries world-wide for the protection of their populations - almost all countries follow the recommendations made by the independent International Commission on Radiological Protection (ICRP). However, from time to time scientific advances make it necessary to consider an adjustment of these estimates and this can be done at a national as well as international level. To illustrate this, a review by NRPB in 1987 of newly published epidemiological studies led to a recommendation to increase the estimate of low dose cancer risk to be used in the UK. This was accepted by Government and within a few years other national and international bodies came to similar conclusions. The HPA, through its Advisory Group on Ionising Radiation (AGIR), continues to assess radiation cancer risks to the UK population. Most recently leukaemia risks have been reviewed ( Docs NRPB 14(1) 2003), a sub-group of AGIR has been formed to examine solid cancer risks.

Last reviewed: 4 September 2008