MORTALITY AMONG UNITED-STATES RADIOLOGIC TECHNOLOGISTS, 1926-90

The possible mortality risk from low level chronic exposures to ionizi ng radiation was evaluated among 143,517 United States radiologic tech nologists certified by the American Registry of Radiologic Technologis ts between 1926-80. This is one of the few occupational studies of pri marily 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 effec t was observed (standardized mortality ratios [SMR] for all causes and all cancers were 0.69 and 0.79, respectively). Lung cancer (429 death s) 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, t he standardized mortality ratio (SMR) for female breast cancer was 0.9 9 (based on 425 deaths); however, breast cancer was significantly elev ated relative to all other cancers in a test of homogeneity of SMRs (r atio of SMRs = 1.3, P < 0.0001). Significant risks were correlated wit h employment before 1940 (SMR = 1.5; 95 percent confidence interval [C I] = 1.2-1.9), when radiation doses were likely highest, and among wom en 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 refere nt group, risk increased with duration of certification among the 1,89 0 women certified before 1940 (P-trend < 0.001). While the findings fo r breast cancer are consistent with a radiation effect, possible miscl assification in exposure (based on number of years certified) and pote ntial confounding associated with reproductive histories preclude a ca usal conclusion.