Recent reassessments of radiation risk estimates: Implications for radiation protection

Abstract

The publication of the 1988 report by the United Nations Scientific Committee on the Effects of Atomic Radiation represents a major step forward in the estimation of the levels of risk associated with exposure to ionizing radiation. Data are now available which quantify the effects of high doses received at high dose-rates in a number of organs and tissues as well as the whole body. The estimates of risk given by UNSCEAR for fatal cancers are up to four times higher than when the Committee last reported in 1977. The main reasons for this change are: firstly, the change in dosimetry of the Japanese survivors of the atomic bombing; and, secondly, the increased epidemiological follow up period, to 1985, which tends to confirm the relative risk model. Uncertainties exist, however, in the numbers of cancers which will arise in irradiated populations that are still alive, and in the extrapolation to low dose. low dose-rate risk factors. Since, in radiological protection, the assumption is made of a linear relationship between dose and risk, it follows that in setting dose limits it is necessary to consider not only the risk per unit dose, but also the limit of tolerable or acceptable risk. In this paper, the question of the limitation of risk is addressed for both members of the public and those occupationally exposed. The same question is being addressed by the International Commission on Radiological Protection in the formulation of their new recommendations. The relationships between dose and risk can be used to speculate on the range of dose levels within which ICRP may set limits. Finally, it is emphasized that, because all exposures will be as low as reasonably achievable, actual doses received would be expected to be below the limits derived in the paper.