Simon and Co-Workers Explained:

Estimation of Radiation Doses to U.S. Military Participants from Nuclear Testing: A Comparison of Historical Film-Badge Measurements, Dose Reconstruction and Retrospective Biodosimetry.

Reference: Simon, S.L., Bailey, S.M., Beck, H.L., Boice, J.D., Bouville, A., Brill, A.B., Cornforth, M.N., Inskip, P.D., McKenna, M.J., Mumma, M.T., Salazar, S.I. and Ukwuani, A. (2019) Estimation of Radiation Doses to U.S. Military Test Participants from Nuclear Testing: A Comparison of Historical Film Badge Measurements, Dose Reconstruction and Retrospective Biodosimetry, Radiation Research, 191, pp. 297-310.

What was the research question?

Scientists use physical methods, genetic methods and, reconstruction of exposure scenarios in order to make estimates of radiation doses received by individuals. The authors of this work wanted to improve scientific understanding of the reliability and the limitations of these methods.

The study involved U.S. nuclear test veterans known to have been exposed to radiation about sixty years ago based on their film badge data (a physical method). The researchers wanted to know if their different methodological approaches would produce similar dose estimates for the veterans and hence be useful for assessing exposure when film badge data is not available.

The research performed in this study with regards to developing a new genetic method was also published in a separate journal article by McKenna and co-workers. The McKenna article places greater emphasis on genetic evidence for exposure and includes a discussion about the usefulness of using chromosome inversions for this purpose. In contrast, the Simon article emphasises reconstruction as the researchers want to apply their method for veterans who received doses too low to be assessed using genetic methods.

How was the scientific problem approached?

Scientists use abnormal chromosomes called reciprocal translocations for long-term retrospective dose estimation (a genetic method), because these aberrations can persist in the body for many years after formation. The scientific team wanted to see whether the reliability of this method could be improved by also taking another abnormality, called inversions, into account.

To perform reconstruction, researchers require details of the duties and activities of each individual veteran at the time of exposure. The American Department of Defence have facilitated this since 2005 by releasing service records for each veteran 62 years after they have left the military. Environmental radiation readings from the nuclear tests have also been declassified over the same period.

What did the research involve?

A new genetic method and historical reconstruction were used to estimate radiation doses for twelve male nuclear test veterans who had received doses of > 200 mSv approximately 60 years ago according to their film badge data.

For details regarding developing this genetic method for dose estimation please refer to the details given in the McKenna lay summary.

For the reconstruction method, service records were obtained for the nuclear test veterans and this was supplemented by interviewing all of them about their activities and duties.

What did they find?

The researchers found that the closest agreement for the three different approaches for dose estimation, was between the estimate obtained by measurement of reciprocal translocations and inversions combined, and the estimate obtained by the more in-depth reconstruction methods. Based on the new genetic and reconstruction approaches the nuclear veterans who served on the Rongerik Atoll received an average dose of 300 mSv – 400 mSv and the veterans who served elsewhere had an average dose of 250 mSv – 300 mSv.

How did the researchers interpret their results?

The researchers state that both their improved genetic method and their new reconstruction method have reliably estimated the dose received by a group of U.S. veterans about 60 years after exposure.

However, they note that the results obtained using their combined genetic method have been shown so far to apply to veterans who were known to have received doses > 200 mSv and even then, eight of the twelve veterans received doses lower than the minimum detectable dose. Their genetic method may not be applicable to the 99% of American veterans who have received lower doses. Thus, they recommend that further studies are conducted to assess the relevance and the limitations of their work.

Overall, they consider their new reconstruction method to be appropriate for further investigation with U.S. test veterans who have received doses too low to be detected biologically.

Who did this research?

This study was done by a team of scientists from Colorado State University in collaboration with other researchers from the University of Texas, Vanderbilt University, the U.S. National Cancer Institute, the International Epidemiology Institute and KromaTiD Inc. This research was funded by the U.S. National Cancer Institute, the U.S. National Institute of Allergy and Infectious Diseases, U.S. Department of Energy and the Vanderbilt-Ingram Cancer Centre.

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