Mortality among United States radiologic technologists, 1926-90.

The possible mortality risk from low level chronic exposures to ionizing radiation was evaluated among 143,517 United States radiologic technologists certified by the American Registry of Radiologic Technologists between 1926-80. This is one of the few occupational studies of primarily women (73 percent) exposed to radiation during their employment. More than 2.8 million person-years of follow-up were accrued through 1990, and 7,345 deaths were identified. A strong healthy-worker effect was observed (standardized mortality ratios [SMR] for all causes and all cancers were 0.69 and 0.79, respectively). Lung cancer (429 deaths) was not increased with available measures of radiation exposure and no significant associations were observed for acute, myelogenous, and monocytic leukemia (74 deaths). Relative to the general population, the standardized mortality ratio (SMR) for female breast cancer was 0.99 (based on 425 deaths); however, breast cancer was significantly elevated relative to all other cancers in a test of homogeneity of SMRs (ratio of SMRs = 1.3, P < 0.0001). Significant risks were correlated with employment before 1940 (SMR = 1.5; 95 percent confidence interval [CI] = 1.2-1.9), when radiation doses were likely highest, and among women certified for more than 30 years (SMR = 1.4, CI = 1.2-1.7) for whom the cumulative exposure was likely greatest. Using an internal referent group, risk increased with duration of certification among the 1,890 women certified before 1940 (P-trend < 0.001). While the findings for breast cancer are consistent with a radiation effect, possible misclassification in exposure (based on number of years certified) and potential confounding associated with reproductive histories preclude a causal conclusion.