Military Global Health Engagement and Low-Dose Ionizing Radiation.

U.S. Military Global Health Engagement is evolving toward more specifically military strategic objectives, as well as better coordination with U.S. diplomacy and international development. The Department of Defense (DoD) issued policy guidance on global health engagement codifying these priorities for the first time in 2013, and is now developing the corresponding implementing instructions and a Joint Concept of Operations. As concepts gel, the time is ripe for new ideas that can help round out military global health engagement’s emerging triple aim of force health protection, partnership building, and threat reduction, and situate these activities effectively within Whole of Government global health efforts. One novel line of effort that is particularly well aligned and currently under-resourced is cooperative military engagement on the scientific problems of low-dose radiation health effects. “Low dose” in the military context means ionizing radiation exposure in the dose range where there is no immediate performance decrement, but there is exposure-related risk of long-term health consequences. In numerical terms as defined by Joint Publication 3-11 (Operations in Chemical, Biological, Radiological, and Nuclear Environments), this range extends from a projected mission cumulative radiation dose of 0.5 milliGray (mGy), where focused monitoring begins, through 50 and 100 mGy as nonpriority tasks are progressively curtailed, to 250 mGy where monitoring for acute radiation effects begins. For comparison, annual cumulative exposure in the U.S. averages about 3 milliSievert (mSv), and the annual U.S. occupational dose limit for radiation workers is 50 mSv. Peacetime radiation protection decisions are driven toward the low end of the occupationally allowable range by the fundamental strategy of keeping exposures As Low As Reasonably Achievable (ALARA), which is also explicitly adopted as overarching DoD policy in Joint Publication 3-11. During Operation Tomodachi, USPACOM took a conservative approach to ALARA, limiting individual cumulative radiation exposure to the equivalent of 3 mGy. Radiation avoidance measures necessary to meet this target included mission-impacting constraints such as deferred maintenance to reduce crew exposures and increased ship standoff distances. After-action analyses identified lack of consistent guidelines to translate detectable radionuclide levels to protective actions, and widespread lack of preparation to implement ALARA decision-making within an evolving emergency. U.S. authorities set the evacuation zone in Japan at 80 km for U.S. nationals, conflicting with the Japanese government’s 20 to 30 km zones despite the challenges for public trust and risk communication that this discrepancy created. Other nations’ advice to their nationals was in some cases even more unilaterally conservative, including sheltering in place out to 250 km. Underlying these challenges is persisting scientific uncertainty about low-dose radiation effects, stemming from biological complexities that are only now becoming possible to address. For example, the study of radiation cancer risks has been limited because cancer arises also in people who have not received excess radiation. Epidemiologic studies of excess risk from radiation have therefore relied on population-level statistics to separate the “signal” of radiation-attributable cancers from the “noise” of biologically indistinguishable cancers occurring through a variety of other pathways. Progressively higher statistical power is needed for epidemiologic study of lower exposures. Thus, it has been estimated *Science Research Department, Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, 8901 Wisconsin Avenue, Bethesda, MD 20889. †Center for Radiological Research, Columbia University Medical Center, Columbia University, 630 West 168th Street, New York, NY 10032. ‡Military Medical Operations, Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, 8901 Wisconsin Avenue, Bethesda, MD 20889. The opinions expressed are those of the authors and are not the opinions of the Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, Department of Defense, or the U.S. Government. doi: 10.7205/MILMED-D-17-00142 i The Gray is a unit of absorbed dose, while the Sievert is a unit of effective dose in a living system. One Sievert is defined as that effective dose produced by one Gray of absorbed dose of x-rays or gamma rays; higher Sievert values are associated with one Gray of neutrons, alpha particles, or other higher energytransfer radiation. In practice, DoD guidance uses Gray because field-deployed measurement technology may not include Sievert readouts.