Controversy continues on whether or not ionizing radiation is harmful at low doses, with unresolved scientific uncertainty about effects below a few tens of millisieverts. To settle what regulatory controls should apply in this dose region, an assumption has to be made relating dose to the possibility of harm or benefit. The position of the Australasian Radiation Protection Society on this matter is set out in a statement adopted by the Society in 2005. Its salient features are:

• There is insufficient evidence to establish a dose-effect relationship for doses that are less than a few tens of millisieverts in a year. A linear extrapolation from higher dose levels should be assumed only for the purpose of applying regulatory controls.

• Estimates of collective dose arising from individual doses that are less than some tens of millisieverts in a year should not be used to predict numbers of fatal cancers.

• The risk to an individual of doses significantly less than 100 microsieverts in a year is so small, if it exists at all, that regulatory requirements to control exposure at this level are not warranted.