Assessing the reliability of dose coefficients for inhaled and ingested radionuclides

Consideration of uncertainties on doses can provide numerical estimates of the reliability of the protection quantities (dose coefficients) used in radiation protection to assess exposures to radionuclides that enter the body by ingestion or inhalation ('internal emitters'). Uncertainty analysis methods have been widely applied to quantify uncertainties on doses, including effective dose. However, it is not always clear how the distributions of effective dose per unit intake that result from such analyses should be interpreted with respect to the intended use of effective dose in radiation protection and the use of dose coefficients as reference values. The ICRP system of radiological protection is reviewed briefly and it is argued that the reliability of an effective dose coefficient as a protection device can best be determined by comparing the nominal detriment adjusted cancer risk associated with the dose coefficient, with a best estimate of risk for the exposure pathway and exposed population group, considering uncertainties in biokinetic, dosimetric and risk parameters. Because it is the uncertainty on the population mean of this quantity that is required, the effect of parameter variability should be distinguished from the effect of parameter uncertainty when performing uncertainty analyses. A methodology for performing the uncertainty analysis is discussed and studies that quantify uncertainty on doses and risk from intakes of radionuclides are reviewed.