Scientific view of low-level radiation risks.

The average number of diagnostic x-ray procedures per year in the United States equals the total population and results in an annual collective effective dose equivalent of about 9 million person-rem. Possible deleterious effects include (a) genetic consequences, the risks of which can be assessed only from animal studies; (b) carcinogenesis, which can be assessed from survivors of nuclear bombings and patients exposed for medical reasons; and (c) effects on the developing embryo or fetus. For stochastic endpoints such as cancer and genetic anomalies, it is estimated that the current practice of radiology in the United States increases spontaneous frequency by less than 1%. No single procedure is likely to produce harm to the conceptus, but an accumulation of procedures in a pregnant woman could be hazardous during the sensitive period of 8-15 weeks after conception, with microcephaly and mental retardation the most likely deleterious effects. The balance of risk versus benefit in diagnostic radiology is heavily weighted toward benefit, but the risks are there, and constant efforts are needed to reduce radiation doses to the minimum necessary.