  There is a considerable debate between research groups applying the two stage
clonal expansion model for lung cancer risk estimation, whether radon exposure
affects initiation and transformation or promotion. The objective of the
present study is to quantify the effects of radon progeny on these stages with
biophysical models. For this purpose, numerical models of mutation induction
and clonal growth were applied in order to estimate how initiation,
transformation and promotion rates depend on tissue dose rate. It was found
that rates of initiation and transformation increase monotonically with dose
rate, while effective promotion rate decreases with time, but increases in a
supralinear fashion with dose rate. Despite the uncertainty of the results due
to the lack of experimental data, present study suggests that effects of radon
exposure on both mutational events and clonal growth are significant, and
should be considered in epidemiological analyses applying mathematical models
of carcinogenesis.
