Leukemia among medical diagnostic X-ray workers in China.

The incidence of leukemia among 27,011 medical diagnostic X-ray workers was compared with that among 25,782 other medical specialists employed between 1950 and 1985 in China. A significantly elevated risk of leukemia was seen among diagnostic X-ray workers. The relative risk (RR) of leukemia was 2.4 (95% CI = 1.3-4.1) based on the rate observed in the comparison group, and 2.3 when the rate in a Shanghai population was used. The elevated incidence of leukemia was restricted to male X-ray workers, and the relative risk of leukemia was higher for X-ray workers who began employment before 1970 than for those who started work more recently. The RR for leukemia was highest among workers who had been employed for 10-15 years, but the incidence was not apparently elevated further among those who had been employed for more than 20 years. The risk was more pronounced in workers who had begun their jobs before the age of 20 years, and it appeared to decrease with increasing age at first employment. The variation in risk with the duration of employment, age and the calendar time when diagnostic radiological work began indicates that the elevated incidence of leukemia is attributable to occupational exposure to X-rays.