Dosimetry Model for Bronchial and Extrathoracic Tissues of the Respiratory Tract

Abstract

The Task Group to Review the Lung Model for the International Commission on Radiological Protection (ICRP) is proposing to revise the dosimetry model for the respiratory tract on the basis of the relative sensitivities of the various tissue components. If all tissues within the lung were to receive the same radiation dose, it is considered that approximately 80% of fatal lung cancers would arise in the bronchi, about 15% in the bronchioles. and only about 5% in alveolar - interstitial tissue, with a very small fraction of cancers (less than 0.1%) in lymph nodes. Tissues in the nose, nasopharynx, mouth, oral pharynx, and larynx are less sensitive than the bronchi or bronchioles, but their contribution to the radiation detriment would not necessarily be negligible if they were to receive a higher equivalent dose than the thoracic airways or other organs. This paper outlines the model proposed by the task group to evaluate doses received by presumed target cells in the various epithelial tissues, to take account of non-uniform irradiation by a.ß. positron and electron emitters, and to derive and equivalent dose for the lung and the extrathoracic region of the respiratory tract for use in ICRPs recommended system of dose limitation. Examples are given of equivalent doses to the respiratory tract that are calculated for several types of a.ß emitter. These new values are compared with the equivalent doses calculated using the ICRP Publication 30 lung model. It is emphasised that the current version of the lung model described here is still provisional.