[ RadSafe ] Uncertainties in estimating health risks associated with exposure to ionising radiation - Abstract - Journal of Radiological Protection - IOPscience

[Cary Renquist]

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Memorandum

The information for the present discussion on the uncertainties
associated with estimation of radiation risks and probability of disease
causation was assembled for the recently published NCRP Report No. 171
on this topic. This memorandum provides a timely overview of the topic,
given that quantitative uncertainty analysis is the state of the art in
health risk assessment and given its potential importance to
developments in radiation protection. Over the past decade the
increasing volume of epidemiology data and the supporting radiobiology
findings have aided in the reduction of uncertainty in the risk
estimates derived. However, it is equally apparent that there remain
significant uncertainties related to dose assessment, low dose and low
dose-rate extrapolation approaches (e.g. the selection of an appropriate
dose and dose-rate effectiveness factor), the biological effectiveness
where considerations of the health effects of high-LET and lower-energy
low-LET radiations are required and the transfer of risks from a
population for which health effects data are available to one for which
such data are not available. The impact of radiation on human health has
focused in recent years on cancer, although there has been a decided
increase in the data for noncancer effects together with more reliable
estimates of the risk following radiation exposure, even at relatively
low doses (notably for cataracts and cardiovascular disease). New
approaches for the estimation of hereditary risk have been developed
with the use of human data whenever feasible, although the current
estimates of heritable radiation effects still are based on mouse data
because of an absence of effects in human studies. Uncertainties
associated with estimation of these different types of health effects
are discussed in a qualitative and semi-quantitative manner as
appropriate. The way forward would seem to require additional
epidemiological studies, especially studies of low dose and low
dose-rate occupational and perhaps environmental exposures and for
exposures to x rays and high-LET radiations used in medicine. The
development of models for more reliably combining the epidemiology data
with experimental laboratory animal and cellular data can enhance the
overall risk assessment approach by providing biologically refined data
to strengthen the estimation of effects at low doses as opposed to the
sole use of mathematical models of epidemiological data that are
primarily driven by medium/high doses. NASA's approach to radiation
protection for astronauts, although a unique occupational group,
indicates the possible applicability of estimates of risk and their
uncertainty in a broader context for developing recommendations on: (1)
dose limits for occupational exposure and exposure of members of the
public; (2) criteria to limit exposures of workers and members of the
public to radon and its short-lived decay products; and (3) the
dosimetric quantity (effective dose) used in radiation protection.