Recording of external radiation exposures at Oak Ridge National Laboratory: implications for epidemiological studies

Accurate measurements of radiation exposure for individuals are critical to assessing radiation-mortality associations. This paper is based on a study of changes in recorded doses and in radiation monitoring programs at Oak Ridge National Laboratory, a U.S. Department of Energy facility where whole body external penetrating radiation exposures have been of primary epidemiological interest. External radiation monitoring data from 1943-1984 are analyzed for a group of white males (N = 8,318). The proportion of workers monitored for external radiation increased from about 50% in 1943 to over 80% in 1944 to above 98% after 1948. Mean radiation doses showed maxima in 1944 and 1957, followed by steady and long-term declines. Numerous changes in monitoring programs occurred during the study period, including changes in the types of dosimeters used, the frequency of reading dosimeters, methods of calculating doses, and practices of recording doses. Temporal patterns of doses in the lower range of the distribution showed some changes suggestive of changes in policies and practices for recording doses, which would influence dose values used in epidemiological studies. Reliable and accurate exposure measurements are especially important in studies of low level exposures due to small differences in outcomes between exposure groups. Evidence of changes in recorded doses due to monitoring and recording practices, rather than to actual changes in exposures in this well-monitored population, suggests the importance of comparable studies of other populations used for epidemiological studies of radiation-mortality associations.