under construction
Introduction
Some of the evidence linking radon-related dose to lung cancer comes from epidemiologic research. I am not an epidemiologist (although I work with some), so what appears below is a non-expert's summary of the current state of radon lung cancer epidemiology.
Epidemiology looks for association between the occurrence of a disease (in this case lung cancer) and suspected causes(in this case the radiation dose to the lungs from radon and its decay products). Epidemiologic studies test the possibility that a cause is associated wit a disease by comparing the disease rate in one (or more) groups of people who have high exposure to the cause with a group who has low (or no) exposure to the cause. Things get a little tricky when the disease, like lung cancer, has more than one suspected cause. Smoking is recognized as the most prevalent cause for lung cancer. Thus, radon studies have to carefully include the effects of the smoking behavior of the different groups that they study. The best study style for a disease that has multiple causes is called a case-control study. Cases are people who currently have the disease, while controls are people without the disease but who have characteristics (like age) that are similar to cases. For a low-frequency disease like radon-induced lung cancer in homes, the most cost-effective study design is retrospective case-control; that is a case control study of people in the present that have the disease.
Retrospective Case-Control Studies
Some of the strongest evidence for radon induced lung cancer comes from case-control studies of underground miners who were exposed to high concentrations of radon decay products at work. The best analysis of the miner data is summarized in a National Academy Report, BEIR VI. The most comprehensive case-control study of residential radon exposure in North America took place in Iowa. It found a significant increase in lung cancer risk from exposure to radon concentrations at and above the USEPA action level. The study results have been published. More work needs to be done to refine and extend the risk factor to lower concentrations. Additional groups need to be included to better understand the effects of tobacco smoke and radon interaction. Unfortunately, no new epidemiologic studies are in progress in North America. Since a comprehensive study requires many years to complete, we will only have the new results from Europe, where housing and population characteristics are frequently quite different, to improve the dose-response relationship.
Studies of the molecular and cellular effects of low doses of alpha particles are underway. These studies may improve our sensitivity to detect radon-specific lung cancers. Extending effects from studies at these levels to the complex human individual is quite complex and tenuous.
Ecological Studies
An ecological study uses the average exposures and cancer rates for a group in a given region rather than the exposures and disease status for each individual used in a case-control study. Epidemiologists use ecologic studies to "inexpensively" test the possibility of some hypotheses. So ecologic studies are the first step in the investigation, not the final answer. Ecologic studies of a disease like lung cancer are not reliable since no good information is available about the exposure of an individual to the multiple causative agents (smoke, radon,...). Dr. B.L. Cohen has conducted the best know radon-lung cancer ecologic study. Dr. Cohen does not use his data to determine whether or not radon causes lung cancer, but to test the hypothesis that radiation doses continue to cause cancers at extremely low dose. This hypothesis, called the Linear No Threshold (LNT) hypothesis, is quite controversial. The debate surrounding tests of the LNT are quite technical and complex. The debate is not concluded, nor is it likely to be in the near future.
More text will follow here in the near future as I study the LNT-radon problem in detail.
Questions/Comments, e-mail: Dr. Steck
Last revised : 30 June, 2004
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