Beir VII : Health Risks from Exposure to Low Levels of Ionizing Radiation
BEIR VII develops the most up-to-date and comprehensive risk estimates for cancer and other health effects from exposure to low-level ionizing radiation . It is among the first reports of its kind to include detailed estimates for cancer incidence in addition to cancer mortality . In general , BEIR VII supports previously reported risk estimates for cancer and leukemia , but the availability of new and more extensive data have strengthened confidence in these estimates . A comprehensive review of available biological and biophysical data supports a “ linear-no-threshold ” ( LNT ) risk model — that the risk of cancer proceeds in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans .
This report is the seventh in a series of publications from the National Academies concerning radiation health effects called the Biologic Effects of Ionizing Radiation ( BEIR ) reports . BEIR VII focuses on the health effects of low levels of low linear energy transfer ( low-LET ) ionizing radiation such as x-rays and gamma rays . The most recent BEIR report to address low level low-LET radiation was the BEIR V report published in 1990 . Humans are exposed to ionizing radiation from both natural and man-made sources ( see Figure 1 ). Very high doses can produce damaging effects in tissues that can be evident within days after exposure . Late effects such as cancer , which can occur after more modest doses including the lowdose exposures that are the subject of this report , may take many years to develop .
Most radiation sources have a mixture of high- and low-LET radiation . Compared to high-LET radiation , low- LET radiation deposits less energy in the cell along the radiation path and is considered less destructive per radiation track . The BEIR VII report defines low doses as those in the range of near zero
Figure 1 . The chart on the left shows the sources of global “ background ” radiation of both high- and low-LET radiation . The figure at right shows the relative contributions of the various types of man-made radiation to the US population . 1 Medical x rays and nuclear medicine account for about 79 % of the man-made radiation exposure in the United States . Substances in consumer products such as tobacco , the domestic water supply , building materials , and to a lesser extent , smoke detectors , televisions , and computer screens , account for another 16 %. Occupational exposures , fallout , and the nuclear fuel cycle comprise about 5 % of the man-made component .
1Figures based on data from Ionizing Radiation Exposure of the Population of the United States , National Council on Radiation Protection and Measurements , No . 93 , 1987 .