The linear no-threshold debate: Where do we go from here?

For the past several years, the LNT (linear no-threshold) theory has come under attack within the scientific community. Analysis of a number of epidemiological studies of the Japanese survivors of the atomic bombings and workers exposed to low level radiation suggest that the LNT philosophy is overly conservative, and low-level radiation may be less dangerous than commonly believed. Proponents of current standards argue that risk conservatism is justified because low level risks remain uncertain and it is prudent public health policy; LNT opponents maintain that regulatory compliance costs are excessive, and there is now substantial scientific information arguing against the LNT model. Regulators use the LNT theory in the standards setting process to predict numbers of cancers due to exposure to low level radiation because direct observations of radiation-induced cancers in populations exposed to low level radiation are difficult. The LNT model is simplistic and provides a conservative estimate of risk. Abandoning the LNT philosophy and relaxing regulations would have enormous economic implications. However, alternative models to predict risk at low dose are as difficult to justify as the LNT model. Perhaps exposure limits should be based on model-independent approaches. There is no requirement that exposure limits be based on any predictive model. It is prudent to base exposure limits on what is known directly about health effects of radiation exposure of human populations. (C) 1998 American Association of Physicists in Medicine.