In particular, the research team from NIOSH (National Institute for Occupational Safety and Health) became interested in K-25's use of photofluorography for chest X-rays of workers until 1956, when an equipment switch was made to the conventional technique still in use.
The photofluorographic technique, which produced an image of the chest on a fluorescent screen, reportedly delivered a radiation dose to the bone marrow that was about 100 times greater than today's X-ray method (800 millirads vs. 8 millirads).
Dr. John Cardarelli, the principal investigator for NIOSH, said researchers raised questions when they came across X-ray films at Oak Ridge that were a different size (4-by-10 inches) than the conventional film size (14-by-17). The smaller images are associated with photofluorography.
The health implications of the discovery are not clear, but the NIOSH team felt the information was potentially significant enough to alter risk estimates for K-25 employees whose work records showed relatively low-dose radiation histories. Indeed, based on a limited study of 45 workers, the exposures from the work-related chest X-rays dwarfed the amount of radiation received from occupational activities at the uranium-enrichment plant.
"This is a very small study," Cardarelli cautioned.
Nonetheless, NIOSH determined that if this information were excluded from an epidemiological study, many of those nuclear workers at K-25 would have been placed in "inappropriate" dose categories.
That's why the team went ahead and reported this issue in a separate paper, even though the major study of mortality rates from multiple myeloma at K-25 won't be completed for at least another year.
Cardarelli said NIOSH researchers planned to use the medical X-ray information in current epidemiological studies and address questions about the historical use of photofluorography in upcoming projects.
All the government's World War II-era nuclear facilities, including Y-12 and X-10 in Oak Ridge, used the photofluorographic technique because it was an economical way to get chest images in large quantity, Cardarelli said. He said he didn't know when the other facilities abandoned the use of photofluorography.
"It all depends on when they purchased new X-ray equipment, which is not something that is purchased very often," he said.
The NIOSH researcher said the photofluorographic technique was widely used in the general population for tuberculosis screening.
Cardarelli said the dose information from medical X-ray records would probably have more impact on studies of workers at relatively low-level radiation facilities, such as K-25, than at facilities in Hanford, Wash., where workers historically received higher radiation exposures.
Of course, this new information also raises questions about previous studies done at K-25 and the other Oak Ridge facilities. How much would this have changed the radiation-dose profiles of Oak Ridge workers? Would it alter risk estimates?
According to the NIOSH report, previous studies of nuclear workers have not included radiation exposures from work-related X-rays for several reasons. For instance, there was a "perception" that the contribution from chest X-rays would be low compared to other sources of radiation at the plant, and "epidemiologists have traditionally assumed that exposures from work-related X-rays would be randomly distributed throughout the working population, so that effects associated with this exposure would not influence the analysis.."
The research team discounted both of those assumptions.
The chest X-rays actually turned out to be the biggest radiation source for some workers, and documents indicated that radiation workers typically received more chest X-rays than other, nonexposed workers, NIOSH said.
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ORNL and Oak Ridge managers planned in the 80's to play up toxic metals and radiation in order to try and loose the effects of fluorides and HF emissions on the worker and community health. While this X-ray news provides higher rad doses to workers, it also detracts from the examination of the fluorides contributions to cancers and chemical illnesses.