Abstract
Occupational X‐ray examination programs have been conducted in many countries to screen for occupational and nonoccupational respiratory diseases, resulting in widespread exposure to X‐radiation. We conducted a multicentre case‐control study of lung cancer in the Czech Republic, Hungary, Poland, Romania, Russia and Slovakia, including 2,589 cases and 2,859 controls enrolled during 1998–2002. We collected detailed information on occupational X‐ray examinations, occupations and tobacco smoking. We calculated odds ratios of lung cancer via multiple logistic regression after adjustment for age, sex, center and tobacco smoking.
Among controls 24.9% reported no X‐ray examination, 62.9% reported 1–30 examinations and 12.2% reported more than 30 examinations. When we chose individuals with no examination as the reference group, the odds ratios of lung cancer were 1.21 (95% confidence interval [CI] 0.99–1.48), 1.33 (95% CI 1.08–1.64), 1.49 (95% CI 1.18–1.87), 1.52 (95% CI 1.17–1.99) and 2.15 (95% CI 1.50–3.08) for 1–10, 11–20, 21–30, 31–40 and more than 40 examinations, respectively (p‐value of test for linear trend <0.0001). The association between X‐ray examinations and lung cancer risk was strong in countries with low prevalence of exposure and absent in countries with high prevalence of exposure. Odds ratios for X‐ray examinations were lower among smokers than among nonsmokers. The magnitude of the increased risk observed is higher than expected on the basis of other studies of radiation‐exposed populations. Although the association we detected between X‐ray examinations and lung cancer risk may reflect a carcinogenic effect of repeated exposure to low‐level ionizing radiation, reporting bias and particularly uncontrolled confounding by occupational exposure to carcinogens are also likely explanations of the results. © 2005 Wiley‐Liss, Inc.