Although I like the report very much from a scientific point of view, I do not agree with its conclusion to use in future a set of reference dose conversion coefficients depending on the exposure conditions, such as aerosol characteristics and equilibrium factors.
I prefer using a single dose conversion factor for both workers and members of the public, and as a value I suggest to select the long-established UNSCEAR conversion factor.
Defining a whole set of different dose coefficients per unit exposure to radon and its progeny ignores the most important factor influencing the radon risk, which is smoking. Indeed, because of its almost multiplicative relationship with radon, a smoker has for the same radon exposure at least a 10 times higher lung cancer risk than a non smoker. As a consequence, changes in the ratio of smokers to non-smokers will result in significant changes in the estimated lung cancer risk. I don't see in this uncertain context the added value of using a set of dose coefficients on the basis of exposure conditions, such as aerosol characteristics and equilibrium factors. Moreover, it has been shown that the equilibrium factor is largely determined by the aerosol characteristics and that in many exposure situations the conditions are compensating, making radon a fairly good measure of the radiation exposure.
Publishing a whole set of reference dose conversion factors based on exposure conditions has in my opinion little benefit and will, on the contrary, complicate the operational radiation protection of the exposed workers and members of the public.
I am in favor of using the single UNSCEAR dose conversion factor for both workers and members of the public. This factor is well within the range of possible dose conversion factors from the epidemiological and dosimetric approaches, as shown in the recent paper published in Health Physics by Marsh et al (99: 511-516; 2010), and does not give a false impression of precision of the lung cancer risk as would do a set of reference dose conversion factors. Moreover, the current worldwide average population exposure from natural radiation sources of 2.4 mSv/y is calculated using the long-established UNSCEAR conversion factor.
I refer to my recent paper in Radiation Protection Dosimetry for the discussion on the reason to select the UNSCEAR dose conversion factor for exposure to radon and its progeny (H. Vanmarcke, Radon: a special case in radiation protection, Rad. Prot. Dos. 130: 76-80; 2008).