The BEIR VI Committee applied recent developments in the comparative dosimetry of radon exposures in mines and homes to evaluate the so-called K-factor used to extrapolate the excess relative risk of lung cancer determined for underground uranium miners to exposures in homes. This paper describes methodological aspects of these developments that were specified ambiguously in the BEIR VI report. Specifically, in the section dealing with dosimetry (Appendix B of the BEIR VI report), the K-factor was unusually defined in terms of exposure to radon gas (Kgas), and not in terms of exposure to potential alpha energy (K). An incorrect value of unity was calculated for Kgas. This implies a value of 0.44 for K. In this paper, we describe how application of the ICRP Publication 66 lung and dosimetric models to evaluate the regional lung dose per unit exposure to potential alpha-energy in mines and homes yields the value of K = unity. This confirms the BEIR VI Committee's choice of K = 1 for application in their risk extrapolation model. The paper also reviews the use of doses to specific sub-cellular targets in the evaluation of K. This yields a somewhat greater divergence in the corresponding estimates of K, but again an overall average value of K = unity. The paper describes the methods used to calculate alpha particle bit probabilities for specific subcellular targets, and the resulting estimates of single- and multiple-hit probabilities obtained for exposures in mines and homes, as a function of the respective exposure rates.
Bibliographical noteFunding Information:
This study was originally carried out in 1997 for the National Research Council's BEIR VI Committee under a Consulting Agreement with the National Academy of Sciences, as input to the Committee's deliberations. The original work has been updated and revised for publication under Contract Order No. 1W-1522-NASX between the USEPA Office of Radiation and Indoor Air (ORIA) and ACJ & Associates, Inc. The authors are grateful to Drs David Pawel and Jerome Puskin (ORIA) for many helpful discussions during the preparation of this paper.
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