Controversy continues over the shape of the dose-response curve describing the risk of stochastic health effects (cancer and hereditary disorders) following exposure to low doses of ionising radiation. Radiological protection is currently based upon the assumption that the dose-response curve has no threshold and is linear in the low dose region. This position is challenged by groups suggesting either that this approach seriously underestimates the true risk at low doses or that low-level exposure results in no risk (a threshold dose exists) or even a beneficial effect (“radiation hormesis”). In this paper, we examine the epidemiological and radiobiological bases of the linear no-threshold model and some of the alternatives that have been proposed. We conclude that the evidence for a material deviation from a linear no-threshold dose-response relationship at low doses is not persuasive and that the standard model provides the most parsimonious description of the available scientific evidence.

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