Radon in the Living Environment, 19-23 April 1999, Athens, Greece 093 799 THE IOWA RADON LUNG CANCER STUDY Phase I: RESIDENTIAL RADON GAS EXPOSURE AND LUNG CANCER R. William Field 1 , Daniel J. Steck 2 , Brian J. Smith 1 , Christine P. Brus 1 , Eileen F. Fisher 1 , John S. Neuberger 3 , and Charles F. Lynch 1 1 College of Medicine, Department of Preventive Medicine and Environmental Health, University of Iowa, Iowa City, IA 52242 USA 2 Physics Department, St. John’s University, Collegeville, MN 56321 USA. 3 Department of Preventive Medicine, University of Kansas School of Medicine, Kansas City, KS 66160 USA. Exposure to high concentrations of radon (222Rn) progeny produces lung cancer in both underground miners and experimentally exposed laboratory animals. The goal of the study was to determine whether or not residential radon exposure exhibits a statistically significant association with lung cancer in a state with high residential radon concentrations. A population-based, case-control epidemiologic study was conducted examining the relationship between residential radon gas exposure and lung cancer in Iowa females who occupied their current home for at least 20 years. The study included 413 incident lung cancer cases and 614 age-frequency- matched controls. Participant information was obtained by a mailed-out questionnaire with face-to- face follow-up. Radon dosimetry assessment consisted of five components: 1) on-site residential assessment survey, 2) on-site radon measurements, 3) regional outdoor radon measurements, 4) assessment of subjects’ exposure when in another building, and 5) linkage of historic subject mobility with residential, outdoor, and other building radon concentrations. Histologic review was performed for 96% of the cases. Approximately 60% of the basement radon concentrations and 30% of the first floor radon concentrations of study participants’ homes exceeded the U.S. Environmental Protection Agency action level of 150 Bq m-3 (4 pCi/L). Large areas of western Iowa had outdoor radon concentrations comparable to the national average indoor value of 55 Bq m-3 (1.5 pCi/L). Excess odds of 0.24 (95% CI = -0.05 – 0.92) and 0.49 (95% CI = 0.03 – 1.84) per 11 WLM 5-19 were calculated using the continuous radon exposure estimates for all cases and live cases, respectively. Slightly higher excess odds of 0.50 (95% CI = 0.004 – 1.80) and 0.83 (CI = 0.11 – 3.34) per 11 WLM 5-19 were noted for the categorical radon exposure estimates for all cases and the live cases. A positive association between cumulative radon gas exposure and lung cancer was demonstrated using both categorical and continuous analyses. The risk estimates obtained in this study indicate that cumulative radon exposure presents an important environmental health hazard. Keywords: case-control studies; dose-response relationship (radiation); epidemiologic methods; epidemiologic studies; lung neoplasms; radon, smoking, women’s health INTRODUCTION To assess the association between radon exposure and lung cancer, we conducted a population-based case-control study of Iowa women aged 40 to 84 who lived in their current home for at least 20 years. Iowa is an excellent location to perform such a study for several reasons: 1) a substantial proportion of Iowa's population resides in the same home for 20 years or more; 2) Iowa has a high quality, National