Both papers analyzed data for a cohort of 8,318 white males employed at ORNL for at least 30 days between 1943 and 1972. In the first paper (JAMA 1991), two types of analyses were performed. The first was a cause-specific mortality analysis comparing the study population to the mortality of white males in the U.S. The second was an analysis of the relationship between protracted exposure to low levels of external penetrating ionizing radiation and mortality within the study population. Compared with the mortality experience of all U.S. white males, relatively low mortality was observed for most causes of death. However, mortality from leukemia was elevated in the total cohort and in workers who had at some time been monitored for exposure to internally deposited radionuclides. The second publication (AJIM 1993) examines the role of possible selection and confounding factors not previously studied. Risks associated with length of time in 15 job categories were considered as proxies for the effects of other occupational carcinogens. The findings suggest that selection factors and potential for chemical exposure do not account for the previously noted association of external radiation dose with cancer mortality.
There are three analytic files in the ORX10A02 data set. The first file (X1UPGEN2) contains demographic and some work history data for the entire cohort. The original study (ORX10A01) contained 8,375 males, but further investigation revealed that 57 individuals in the original cohort were not white males. The second file (X1UPFLAT) contains annual and cumulative external whole-body doses for each individual. The third file (X1UPJTGB) contains a record for each individual, including the unique job title of the individual and the number of days, by year, that the person retained the job title.
Vital status was ascertained for 91.8% of the cohort (96.5% of potential person-years of follow-up), and 1, 524 deaths were identified by the end of 1984, the study end date. Death certificates were obtained for 1,490 (97.8%) of these deaths. External radiation monitoring data were used to compile annual and cumulative whole-body doses. For the 4.9% of the work-years for which external monitoring data were not available, doses were estimated. By using internal monitoring data qualitatively as a "yes/no" indicator of potential exposure to internal radiation, workers who had at some time been monitored for internal exposure (N = 3,763) generally had higher external doses; 50% of those ever monitored, but only 8% of those never monitored, for internal exposure had cumulative external doses greater than 1 rem (10 mSv).
ORNL began monitoring personnel for exposure to external penetrating radiation, primarily gamma rays, in 1943. Pocket chambers were used until June 1944, when film dosimeters (film badges) became the primary dosimeter. Film dosimeters were used for personnel monitoring until 1975, when they were replaced with thermoluminescent dosimeters (TLDs). From 1943 until the early 1950s, the usual practice was to provide personal dosimeters to only those workers entering designated areas where there was a potential for exposure. Subsequently, all workers at ORNL were monitored.
Based primarily on the potential for contamination from their work area, some workers were monitored for internal exposure to radionuclides beginning in 1951. Additional workers were monitored to evaluate exposures incurred during incidents. Internal exposures were determined by examining results of urine and fecal bioassays and whole-body counting. Quantitative dose estimates due to internally deposited radionuclides are not available because they usually were not required to be calculated in the past. Also, all of the basic data needed to compute doses for the many radionuclides used at ORNL are not computerized. However, knowledgeable plant health physicists and dosimetrists state that the majority of internal monitoring results for this cohort suggest small internal doses, especially when compared to external doses.