IMPLICATIONS OF AIRWAY RETENTION FOR RADIATION-DOSES FROM INHALED RADIONUCLIDES

A slow phase of bronchial and bronchiolar clearance ('airway retention ') has been included in the revised dosimetric model for the human res piratory tract recently adopted by the International Commission on Rad iological Protection (ICRP), based primarily on the results of the bol us clearance experiments conducted by Stahlhofen et al. The treatment of airway retention in the new ICRP model is described An analysis was carried out of the sensitivity of the equivalent lung dose, and the e ffective dose, to assumptions made in the new model about the extent o f airway retention. It was shown that inclusion of airway retention of material deposited in the bronchial tree does have a significant effe ct on both end-points (of the order of 10-50%) for a wide range of rad ionuclides. In some cases, notably moderately soluble forms of long-li ved alpha-emitters, its inclusion increases these doses by up to a fac tor of three, so that it makes the dominant contribution to the calcul ated dose. The model assumes that material in transit through the bron chial tree, having initially deposited in the alveolar region, is not subject to airway retention. Including retention of this material woul d typically increase doses by a further factor similar to that resulti ng from the airway retention of the bronchial deposit.