Cancer Incidence and Risk Estimation Among Medical X-Ray Workers in China, 1950–1995

Abstract

Cancer incidence (1950-1995) among 27,011 medical diagnostic x-ray workers was compared by means of O/E system with that of 25,782 other medical specialists employed between 1950 and 1980 to provide evidence of human malignant tumors produced by protracted and fractionated exposure to ionizing radiation and to assess resultant cancer risk. Significant cancer risk was seen among diagnostic x-ray workers (RR = 1.2, 95% CI: 1.1-1.3). Significantly elevated risks were found for leukemia and cancers of skin, female breast, lung, liver, bladder, and esophagus; the RRs were 2.2, 4.1, 1.3, 1.2, 1.2, 1.8, and 2.7, respectively. The patterns of risk associated with years since beginning x-ray work and with age and calendar year of initial employment suggest that the excesses of leukemia, skin cancer, and female breast cancer-and possibly thyroid cancer-were related to occupational exposure to x rays. Because of a lack of individual dosimetry for Chinese medical x-ray workers (CMXW) before 1985, the dose was reconstructed by physical and biological retrospective dosimetry methods. The cancer risk of CMXW was estimated based on the reconstructed dose. The average cumulative dose for the earlier cohort (employed before 1970) was 551 mGy, and for the later cohort (employed from 1970 to 1980) it was 82 mGy. The RRs of leukemia and solid cancer were significantly high for the earlier cohort: 2.4 for leukemia, 1.2 for solid cancer. But no significant increase of RR was evident for the later cohort. The RR of leukemia was 1.7 and 1.1 for solid cancer. This means a significant cancer risk can be induced by long term fractionated exposure to ionizing radiation when the cumulative dose reaches a certain level.

Cancer and other causes of mortality among radiologic technologists in the United States

“…29,30 However, only 2 other studies of medical radiation workers included sufficient numbers of females to enable an evaluation of the effects of chronic lowto-moderate doses of radiation on breast cancer. A study of Chinese medical radiation workers (n ϭ 27,011 total, including 5,443 females) found a significantly increased incidence risk of breast cancer among females overall (RR ϭ 1.34), 7 while a small Danish study (n ϭ 4,151 total, 82% female) observed no evidence of elevated risk of breast cancer. 10 Our results for the radiogenic leukemias are generally consistent with the body of evidence for radiation effects associated with this 1 All relative risks were stratified for attained age, calendar year of follow-up, race and gender, and adjusted for employment in other time periods.…”

“…Excess risks of leukemia have been reported among male Japanese technologists employed during 1918 -1971 8 and among Chinese medical radiation workers exposed during 1950 -1985. 7 Elevated risks of leukemia were also observed among nuclear workers who were similarly exposed to chronic doses. 31 Unlike our study, cancer risk estimates for nuclear workers have been linked with individual dose measurements.…”

“…The analyses for all years worked were adjusted for the duration of employment using multifilm procedures and the analyses for all time periods were adjusted for the year first worked with multifilm procedures.-3 p-trend was based on the slope of the corresponding continuous variable; parentheses indicate negative slope estimate.- 4 Relative risks for all years worked adjusted for total duration of employment with multifilm procedures; relative risk for all time periods adjusted for year of first employment with multifilm procedures.- 5 Subjects who never worked with multifilm or who had unknown values for the variables in the table were included in this analysis and were coded as separate categories (estimates not shown). Only female subjects included for the breast cancer analysis; all subjects included for all the other analyses.- 6 Referent group for the joint analyses of the number of years worked and year first worked.- 7 Referent group for the separate analyses of number of years worked and year first worked.-8 p Ͻ 0.05.…”

“…4,5 Some, 7,8 but not all, 9,10 cohorts of radiologic technologists experienced an elevated leukemia risk. None of the earlier studies reported risks in relation to individual lifetime work histories, and only a few 7,10 included female technologists.…”

Melanoma Epidemiology and Prevention

“…Cohort studies of electrical and electronics workers [146,203,220] along with at least one case-control study [179] have also shown elevated risks for melanoma. It has been hypothesized that workers in occupations exposed to ionizing radiation might also be at increased risk of melanoma [3,71,218,238,252].…”