|A Working Party of the Main Commission (MC) of the ICRP met at HPA Chilton, on 12/13 January 2012 to discuss a draft position on radon dose conversion methods and factors, and reference levels, to be proposed to the ICRP Main Commission at the April 2011 meeting. The MC Working Party was chaired by John Cooper and consisted also of Jacques Lochard, Chris Clement, John Harrison, Jean-Francois Lecomte, Doug Chambers, and Ches Mason and with the agreement of Claire Cousins, John Takala was invited to participate in this Working Party. The Working Party met for two days. A summary record of the Working Party meeting ("Report") was prepared and distributed to the MC.
In an email of 10 May to the Working Party, John Cooper noted that the Working Party’s Report had been discussed by the MC at its recent meeting in Paris and that the MC had accepted the conclusions in the Report and would take them into account in the post-consultation revision of the Task Group 81 Report ‘Radiological Protection against Radon Exposure ’ , and in the development of dose coefficients. Dr. Cooper’s email also indicated that the Working Party’s conclusion about the relevance of smoking (and other factors) on the development of the system of radiological protection will be discussed at the next MC meeting.
During the Working Party meeting at Chilton this past January, it was agreed that I would prepare a short discussion(s) on selected issues concerning the "role" of smoking on the selection of a "detriment-adjusted nominal risk coefficient" and on dose conversion factors calculated using the dosimetric approach for consideration for inclusion in the ICRPs Task Group 81 Report. My draft "proposed" text, respectfully submitted for consideration follows.
In reviewing the 6 Dec 2011 Draft "Radiological Protection against Radon Exposure ", I identified several potential locations where an insert on the subject of smoking/risk/dosimetry might be considered. The proposed locations for the inserts are only suggestions and other locations/inserts may be preferred on reflection. Proposed inserts are in italics .
Lines 852 to 858 (Para 33) show the large differences in lung cancer risk depending on the combination of radon exposure and smoking. However, the wording is somewhat different in the discussion of the WHO guideline (line 884 to 888) which does not as clearly address the difference. In view of the importance of smoking as by far the leading cause of lung cancer, the following inserts are proposed
In line 193 (paragraph (d))
Replace "…the Commission now recommends a detriment-adjusted nominal risk coefficient for a population of all ages…" by
"…the Commission now recommends a detriment-adjusted nominal risk coefficient for
a mixed population of smokers and non-smokers and all ages …."
Insert following paragraph (k)
Smoking tobacco is the predominant cause of lung cancer. Exposure to radon is the second leading cause of lung cancer after tobacco smoking. The increase in risk of lung cancer from radon exposure to an individual is more strongly determined by the smoking history than by the radon exposure. Anti-smoking promotion policies have significantly reduced and will continue to reduce smoking prevalence. This decrease in smoking prevalence rate is expected, in time, to result in a corresponding decrease in both the smoking related incidence of lung cancer and also the risk from radon for combined smoking/non smoking populations. Added benefits are the consequent reduction over time of other health risks and medical costs associated with smoking.
Insert to be appended to or follow Para (32)
While the discrepancy between these two quite different approaches is now less than previously, it should be understood that there are a number of confounding variables both in the epidemiology and in the radon dosimetry that have potential to affect the apparent agreement between the two approaches. Key among these is the smoking prevalence in epidemiological studies of miners compared to current or anticipated smoking prevalence. In addition, radon dose models need further development to fully account for the effect of smoking. Moreover, the aerosol parameters for mines on which dosimetry relies, is known to be quite variable, which combined with very limited relevant measurement data for past and current mines, suggests that additional work is needed to define the exposure scenarios for miners and to obtain additional data on mine aerosol conditions that may affect the calculation of dose and its interpretation.
Insert following last bullet in paragraph (33)
It should be noted that the nominal risk coefficient given above has been derived for a mixed population of smokers and non-smokers of all ages, based on the combined risk from tobacco smoke and radon.
Insert to be Appended to or following Para (73)
Prolonged smoking is well established not only as the main cause of lung cancer but also indirectly as an important cause of death from vascular disease and other causes. (e.g., Peto 1992, Thun and Heath 1997). Currently, relative risk models for radon induced lung cancer are the norm. In such models, the excess risk is proportional to the risk of lung cancer in the underlying populations, and hence, a reduction in smoking prevalence is expected to be followed, after a lag, by a decrease in the risk of lung cancer as has for example been observed in Canada (Canadian Cancer Society 2012). In calculating effective dose (Sv), the ICRP first calculates the absorbed dose (Gy) to the various organs and tissues of the body. The absorbed doses are then converted to equivalent dose (Sv) using radiation weighting factors (w
R values) and subsequently, summing values of equivalent dose adjusted by tissue weighting factors (wT) to provide a single value of effective dose. In the future, a further adjustment based on a consideration of an average smoking prevalence may be used for lung cancer.
Insert to be appended to or follow Para (107)
As previously indicated, there is wide variation of the dosimetric relevant parameters across workplaces in a mine. In addition, numerous possible exposure scenarios of where and how long miners work in various locations need to be considered. Thus, there is uncertainty in determining the reference parameter values (and ranges) needed to support the reference dose calculations and how such calculations should be interpreted. Hence, additional work is needed to define the exposure scenarios for miners and to obtain additional data on mine aerosol conditions that may affect the dosimetric calculation and its interpretation.
Insert to be Appended to Para 171
Nominal radon and progeny dose coefficients will be calculated using the dosimetric approach for only two reference exposure conditions: (a) buildings and (b) mines, using a reference particle size distribution, unattached fraction, breathing rate, and equilibrium factor for each of these two cases. The recommended default conversion factors will be given in terms of effective dose to a mixed population of smokers and non-smokers. Given the potentially dominating impact of smoking prevalence, departure from
the given coefficients (e.g., to account for other particle sizes or equilibrium factors) is normally not warranted and should only be considered in compelling circumstances.
The above comments are submitted on behalf of Ches Mason, John Takala and myself.