Occupational X-ray examinations and lung cancer risk

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.