Dosimetric and epidemiological approaches to assessing radon doses--can the differences be reconciled?

A significant problem in internal radiation dosimetry is the discrepancy between the radiation dose from exposure to radon inferred from epidemiological studies and the higher dose calculated using the Human Respiratory Tract Model (HRTM) adopted by the International Commission on Radiological Protection (ICRP). The difference is a factor of about 3. The agreement between these two assessments by radically different approaches is surprisingly good. Nevertheless, there has been concern to understand fully the reasons for this discrepancy and to attempt to reconcile the two approaches. This is of importance because radon contributes about half of the total effective dose from natural background radiation. Furthermore, the HRTM was developed with application to radon exposure in mind, yet at present it is not used for risk assessment purposes although ICRP does suggest that it is useful for comparative dosimetry.