Microdosimetric calculation of absorption fraction and the resulting dose conversion factor for radon progeny

It is an established fact that radon progeny can induce lung cancers. Howev er, there is a well-known discrepancy between the epidemiologically derived dose conversion factor for radon progeny (4 mSv/WLM) and the dosimetricall y derived value (15 mSv/WLM) (mSv is a unit of the dose while WLM is a unit of exposure to radon progeny). Up to now there is no satisfactory explanat ion to this. In the present study we propose that microdosimetry will help reduce the discrepancy significantly. The ICRP Human Respiratory Tract Mode l (HRTM) has been applied to calculate the effective dose conversion factor . All parameters have been kept at their best estimates. Modifications were made in the calculation of the absorbed fractions of alpha particles. In c ontrast to the ICRP approach where the energy has been considered to be dep osited in the layer containing the sensitive cells, we used a microdosimetr ic approach in which the alpha particles deposit their energy only in the n uclei of sensitive cells. This modification alone has lowered the dose conv ersion factor by about one-third (from 15 mSv/WLM down to approximately 10 mSv/ WLM).