Research on Health Effects of Low-Level Ionizing Radiation Exposure: Opportunities for the Armed Forces Radiobiology Research Institute (2014)

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Introduction and Background

This chapter provides basic information about the motivation for and the conduct of the study summarized in this report, beginning with an overview of the issues related to the health effects of exposure to low-dose ionizing radiation and the interest of the organization that requested the report—the Uniformed Services University of the Health Sciences (USUHS) of the U.S. Department of Defense (DoD)—on this subject. It then presents the statement of task for the committee responsible for conducting the study and discusses the committee’s approach to its task. Summary information on related reports from the National Academy of Sciences (NAS) is presented, and the chapter concludes with a description of this report’s organization.

THE ISSUE OF LOW-DOSE IONIZING RADIATION HEALTH EFFECTS

Any discussion of low-dose radiation health effects requires defining what low means. Although often a relative term, major national and international advisory bodies such as the International Commission on Radiological Protection (ICRP) (2007), United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (2010), and the National Research Council (NRC) (2006) have defined low doses as those in the range of 100 mGy and below. This definition is intended to roughly describe the dose below which there is scientific uncertainty about the associated radiation health effects. However, for the nonspecialized public, low-dose often corresponds to doses equal to or about the radiation received from

natural background and could therefore range from about 1–5 mGy.¹ On the other hand, for the health professional who treats cancer patients and aims to kill cancer cells with radiation, a low-dose procedure would utilize radiation of several Gy.

This report is intended to provide advice to the Armed Forces Radiobiology Research Institute (AFRRI) about its role in low-dose radiation health effects research. When the committee asked for guidance on what “low-dose” means for AFRRI, which has traditionally focused on radiation doses high enough to cause acute radiation syndrome, it was told that low-dose radiation was generally interpreted to mean doses that produce no observed acute radiation effects—that is, doses lower than approximately 1 Gy (Huff, 2013).

For consistency with ICRP, UNSCEAR, and NRC literature, the report uses their definition of a low dose: 100 mGy and below. However, to fully address its statement of task (detailed later in this chapter) and provide useful advice to AFRRI, its discussions cover a broader range of doses where appropriate. Doses on the order of 1 Gy are referred to as moderately high; doses of 10 mGy and below, very low.

Human health effects from exposure to ionizing radiation were first noted in the late 1800s and have received a great deal of attention from researchers and the public since World War II (Inkret et al., 1995). Recent events have served to heighten this interest: concerns about terrorist attacks involving improvised nuclear devices and dirty bombs, releases of radioactive materials into the environment from major nuclear accidents in Ukraine (Chernobyl) and Japan (Fukushima Daiichi), increasing exposure to radiation from diagnostic medical procedures, and increasing exposures to radiation arising from the rapid proliferation of radiation-based imaging devices for homeland security.

At high doses (several Gy), health concerns relate primarily to acute radiation syndromes that may lead to death or severe injury. These high-dose effects are reasonably well characterized, although information is still lacking for many realistic situations, such as mixed radiation fields (for example, those involving a combination of X-rays, neutrons, and alpha particles), combined injuries (radiation plus burns plus traumatic injury), and individual variations in radiosensitivity. Active areas of research on high-dose exposures include countermeasures to respond to such insults, biodosimetry to estimate doses, and pharmacologically based radiation mitigators (Pellmar et al., 2005).

The 2011 Fukushima Daiichi accident drew attention to shortcomings in the understanding of the health effects of exposure to low-dose ionizing

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¹ The average natural background radiation in the United States is about 3 millisieverts (mSv) (NCRP, 2009).

radiation (Dauer et al., 2011). This confusion arises in part because regulatory agencies assume that there is no radiation dose below which the health risk is zero when, in reality, there are insufficient data and understanding to know whether this is actually the case (Brenner et al., 2013).

Although a large-scale radiological event is perhaps the most obvious exposure of concern, other important exposures, such as cleanup of radioactively contaminated sites and the rapid increase in radiation-based medical procedures, require an understanding of low-dose radiation risks that is currently unavailable. Apart from human health issues, these topics have major economic consequences for the nation. For example, the current cost of cleanup at the Hanford Site² in Washington State is estimated to be $114.8 billion (Cary, 2013), a figure that is the result of exposure limits and cleanup criteria that are based on science that is characterized by large uncertainties.

The U.S. military has a particular interest and stake in understanding the effects of exposure to ionizing radiation. Response to nuclear threats has been a critical part of its planning process since the Trinity atomic test detonation in 1945, and DoD has long recognized the importance of maintaining a strong health-effects research program. The U.S. Navy Bureau of Medicine and Surgery proposed in 1958 that a bionuclear research facility be established to study such issues (DTRA, 2002; Tenforde, 2011). Public Law 86-500 (June 8, 1960) authorized construction of a laboratory and vivarium under the auspices of the Defense Atomic Support Agency (DASA) and, on December 2, 1960, the three surgeons general of the armed services and DASA approved a charter to create AFRRI (DTRA, 2002). DoD Directive 5154.16, issued May 12, 1961, formally established the Institute. AFRRI was given the mission to “preserve the health and performance of U.S. military personnel and to protect humankind through research that advances understanding of the effects of ionizing radiation” (AFRRI, 2013a).³

Service members may encounter low doses of ionizing radiation from many sources, including situations similar to those found in industry, medicine, nuclear power, and research settings in addition to the exposures resulting from military operations (Blake and Komp, 2014). The U.S. Department of Veterans Affairs (VA) recognizes that some of these may have health consequences and provides health care and other benefits to exposed persons. Currently, those circumstances include service in response to the Fukushima accident; occupational exposures to weapons technicians

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² The Hanford Site is a former nuclear weapons production facility created in the 1940s as part of the Manhattan Project. Operations at the site generated large amounts of waste contaminated with radionuclides and other hazardous substances. Cleanup of the site is considered one of the most complex remediation projects in the history of U.S. weapons production (DOE, 2013).

³ Chapter 4 gives a more complete history of AFRRI.

and medical and dental technicians; and exposure to depleted uranium from explosions, tank armor, or bullet fragments. The VA also recognizes ionizing radiation exposures from work associated with nuclear weapons testing; the occupation of Hiroshima and Nagasaki, Japan; service at McMurdo Station, Antarctica, where the U.S. Navy operated a nuclear power plant that experienced a leak; service at LORAN (Long Range Navigation) stations, which formerly used high-voltage vacuum tubes that generated X-ray radiation; and pilots, submariners, divers, and other service members who received nasopharyngeal radium irradiation treatments from 1940 until the 1960s to prevent damage from pressure changes (VA, 2013).

Because the use of radioactive materials in medical, industrial, power, and military technology is likely to continue; and because military personnel may need to operate in environments contaminated by accident or hostile action, the DoD has a clear interest in understanding the health effects of exposure to low-dose ionizing radiation.

STATEMENT OF TASK

In 2012, USUHS—which currently holds organizational responsibility for AFRRI—requested that the Institute of Medicine (IOM), in concert with the Nuclear and Radiation Studies Board of the NRC,⁴ examine recent scientific knowledge about the human effects of exposure to low-dose radiation from medical, occupational, and environmental ionizing-radiation sources, focusing on the work of and opportunities for AFRRI. The committee convened to conduct this examination was asked to address four items.

1. Identify current research directions in radiobiological science related to human health risks from exposures to low-level ionizing radiation.
2. Assess how Armed Forces Radiobiological Research Institute programs are advancing research along these directions.
3. Identify opportunities for the Armed Forces Radiobiological Research Institute to advance its mission for understanding human health risks from exposures to low-level ionizing radiation, with special emphasis on Department of Defense military operations and personnel.
4. Assess the demand for radiobiology researchers and examine workforce projections. If workforce projections are inadequate to meet demand, suggest ways to accelerate training and investigator development.

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⁴ The Institute of Medicine and the National Research Council are, along with the National Academy of Engineering, operating components of the National Academy of Sciences.

The committee understood its task to encompass a consideration of the organizational structure and funding mechanisms that would promote the successful conduct of low-dose ionizing radiation research by the Institute.

THE COMMITTEE’S APPROACH TO ITS TASK

NAS convened a committee of twelve experts in radiobiology, health physics, medical physics, epidemiology, statistics, risk science, and workforce and training issues to respond to the statement of task. The committee partitioned their assessment into four research areas: countermeasures, dosimetry and biodosimetry, combined injury, and epidemiology. Their examination was focused on information published since major comprehensive reviews by other scientific bodies: the NRC’s Health Risks from Exposure to Low Levels of Ionizing Radiation (known as the “BEIR VII” report [NRC, 2006]) and UNSCEAR’s 2008 Report to the General Assembly (UNSCEAR, 2010). The committee conducted an extensive examination of relevant research in the course of its work. It did not review all such literature but attempted to cover the work that it believed to have been influential in shaping policy and practice at the time it completed its task in late 2013.

The committee and staff also engaged in other information-gathering activities. AFRRI leadership presented their charge to the committee in May 2013 and answered their questions regarding the elements of the statement of task, the operation of the Institute, and the guidance that would be most useful to it (Huff, 2013). A subcommittee toured the AFRRI facilities in Bethesda, Maryland, in July 2013 to better understand the organization’s capabilities and discuss current research with its investigators. The tour also gave the attendees the opportunity to familiarize themselves with the Institute’s physical plant and its capabilities. Additional information was obtained in AFRRI’s responses to three sets of questions submitted by the committee (AFRRI, 2013b,c,d). Staff and committee members attended meetings of professional associations⁵ and educational sessions⁶ related to the topics under consideration to learn about the latest research developments and engage with other experts. The committee also considered information presented at a series of open sessions held in conjunction with

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⁵ (NCRP) National Council on Radiation Protection and Measurements. 2013. 49th annual meeting, Radiation Dose and the Impacts on Exposed Populations, March 1–12, Bethesda, MD.

⁶ NCRP. 2013. Workshop: Where Are the Radiation Professionals?, July 17, Arlington, VA; Radiation Injury Treatment Network and Centers for Medical Countermeasures Against Radiation. 2013. Workshop: Mitigation and Treatment of Radiation Damage, July 31–August 2; AFRRI. 2013. Conference: Military Radiobiology Research in the 21st Century: Threats, Triage, and Treatment, August 26–28, Bethesda, MD.

its meetings, at which experts were invited to offer their views and engage in colloquy with them. Agendas from these events are contained in Appendix A. Materials submitted by members of the public were also considered.

NAS REPORTS ADDRESSING RELATED TOPICS

A number of the IOM and the NRC reports have addressed topics relevant to the issues under consideration here: the health effects of exposure to low-dose ionizing radiation; military radiation-exposure concerns, notably depleted uranium (DU); radiation exposure in other populations, including civilians; and the scientific research workforce. Salient publications are summarized below.

Health Effects of Exposure to Low-Dose Ionizing Radiation

Committees on the Biological Effects of Ionizing Radiation (BEIR) of the NRC have advised the U.S. government on the health consequences of ionizing radiation in a series of reports that began in the 1950s.⁷ The most recent publication, Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII: Phase 2, focuses on the development of risk estimates for low linear energy transfer (LET), radiation doses less than 100 mSv. That report includes a comprehensive literature review of the relevant epidemiological evidence and in-depth descriptions of other biological effects. This committee concluded that the then current scientific evidence was consistent with the hypothesis that a linear dose-response relationship exists between exposure to low-LET radiation and cancer in humans, even at low doses, but that more information is needed to understand noncancer and heritable radiation effects (NRC, 2006).

Military Radiation Exposure Concerns

At the request of the Surgeon General of the U.S. Army, the Committee on Battlefield Radiation Exposure Criteria examined the technical and ethical aspects of military radiation protection and safety in instances of exposure to radiation doses too low to elicit acute effects but associated with long-term cancer risk. That effort focused on radiation doses up to 700 mSv. The initial, interim report—An Evaluation of Radiation Exposure Guidance for Military Operations—reviewed draft North Atlantic Treaty Organization (NATO) radiation-protection guidance on dose limits, documentation, and control measures (IOM, 1997). Among its recommenda-

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⁷ Earlier reports in the series were written under the aegis of the committees on the Biological Effects of Atomic Radiation (BEAR) (NAS, 2014).

tions were that the Army develop specific protocols for managing low-dose exposure situations and that they

Potential Radiation Exposure in Military Operations: Protecting the Soldier Before, During, and After was released 2 years later. This report considered the ethical questions surrounding the decision to put individuals at risk of harm; methods to protect soldiers while meeting military objectives; policies for recording, maintaining, and using individual dose information; and programs to identify potential adverse health effects appearing long after exposure. It recommended that “[m]ilitary personnel should receive appropriate training in both radiation effects and protection in a way that neither inappropriately minimizes effects nor creates unwarranted fear” (IOM, 1999, p. 2).

After the 1991 Persian Gulf War, a number of returning veterans began reporting health problems that they believed to be associated with their service. Under a congressional mandate, the IOM initiated a report series reviewing a wide array of biological, chemical, and physical agents present in the theater of operations to evaluate whether exposure might be responsible for particular health outcomes. DU, a weakly radioactive and toxic heavy metal, has been used in both munitions and protective armor for tanks since the 1980s because its high density has desirable offensive and defensive armor-penetration characteristics. As a result, military personnel have inhaled or swallowed DU particulates and suffered injuries from DU shrapnel and fragments during combat.

Health effects possibly associated with exposure to DU have been considered in multiple volumes in the IOM report series. In a 2000 report, Gulf War and Health, Volume 1: Depleted Uranium, Sarin, Pyridostigmine Bromide, and Vaccines, a committee concluded that there was not enough evidence to draw conclusions as to whether long-term health problems were associated with DU exposure (IOM, 2000). The IOM updated its review in 2008, focusing on literature published since the first effort. That report, Gulf War and Health: Updated Literature Review of Depleted Uranium, determined that there continued to be inadequate or insufficient evidence to determine whether an association exists between in-theater exposure and the cancer and noncancer health outcomes examined. However, the report noted that “[t]he period of followup in several studies might have been too short to detect some diseases that are typically characterized by long latency” and that exposure characterization was inadequate in many

of the studies reviewed by the committee (IOM, 2008a, p. 5). A subsequent report, Gulf War and Health, Volume 8: Update of Health Effects of Serving in the Gulf War (IOM, 2010), did not identify any new literature that would change these conclusions.

Two additional reports released in 2008 also addressed DU. The first, Epidemiologic Studies of Veterans Exposed to Depleted Uranium: Feasibility and Design Issues, examined several options for conducting such research and concluded that the lack of accurate and complete individual-level exposure information on military personnel would make it difficult to design a retrospective study of DU-related health outcomes but that a prospective study might yield useful information should future military operations entail exposure to the substance (IOM, 2008b). The second report, Review of Toxicologic and Radiologic Risks to Military Personnel from Exposure to Depleted Uranium During and After Combat, was produced by an NRC committee. On the basis of their review of epidemiological, radiological, and toxicokinetic data, the committee found that the kidneys are the most sensitive target of uranium toxicity but that “[e]vidence on the risk of cancer or other chronic diseases after exposure to DU in Gulf War soldiers is inadequate” (NRC, 2008a, p. 4).

Radiation Exposure in Other Populations

The report Managing Space Radiation Risk in the New Era of Space Exploration examined factors influencing the exposure of astronauts to ionizing radiation and offered a strategic plan for developing appropriate mitigation capabilities. The study concluded that the lack of knowledge about biological effects of radiation encountered in space is the single most important factor limiting the prediction of risk associated with human space exploration and recommended that the National Aeronautics and Space Administration (NASA) invest in research on that topic (NRC, 2008b).

Technical Evaluation of the NASA Model for Cancer Risk to Astronauts Due to Space Radiation (NRC, 2012d) considers the components, input data (for the radiation types, estimated doses, and epidemiology), and associated uncertainties in a model developed to assess health risks for current and potential future missions. The report also identifies gaps in NASA’s current research strategy for reducing the uncertainties in cancer induction risks. It concludes that, although many aspects of the space radiation environments are now relatively well characterized, important uncertainties still exist regarding biological effects and thus regarding the level and types of risks faced by astronauts.

Assessing Medical Preparedness to Respond to a Terrorist Nuclear Event summarizes a workshop conducted by the IOM under the sponsorship of the U.S. Department of Homeland Security that assessed medical

preparedness to respond to the detonation of an improvised nuclear device. The workshop included a presentation by COL John Mercier, Ph.D.—then Senior Health Physicist at AFRRI and Director of Military Medical Operations—on the U.S. military’s approach to prompt treatment of personnel with combined injuries in the event of a nuclear attack and how this approach might be adapted to the civilian setting (IOM, 2009).

In 2010, the U.S. Nuclear Regulatory Commission (U.S. NRC) requested that the NAS provide an update of a 20-year-old assessment of cancer risks in populations near U.S. NRC–licensed nuclear facilities that use or process uranium for the production of electricity. Analysis of Cancer Risks in Populations Near Nuclear Facilities: Phase 1 focuses on issues related to conducting a scientifically valid epidemiological study. Prominent among these were the challenge of assessing risks at low doses, weak exposure characterization for the populations of interest, and the uncertainties surrounding low-dose health effects (NRC, 2012a). Phase 2 of the study, which is planning a pilot study of cancer risks, was in progress at the time that this report was completed in late 2013.

Research Workforce

Advancing Nuclear Medicine Through Innovation (NRC and IOM, 2007) reported on a number of issues related to the practice of nuclear medicine, including the state of the workforce. It concluded that there are shortages of both clinical and research personnel in all nuclear medicine disciplines (chemists, radiopharmacists, physicists, engineers, clinician-scientists, and technologists) and that training of the next generation of professionals has not kept up with current demands (p. 129).

In 2012, the NRC released Assuring a Future U.S.-Based Nuclear and Radiochemistry Expertise. The authoring committee had been charged with examining the demand for nuclear chemistry expertise and the supply of incoming skilled experts. The committee noted that although the demand for nuclear chemistry expertise was unlikely to decrease, the current labor force is approaching retirement age, with fewer incoming students in the field. To avoid a gap between supply and demand, the committee recommended ways to increase student interest through such steps as on-the-job training opportunities (NRC, 2012b).

Nuclear Physics: Exploring the Heart of the Matter (NRC, 2013) reported that labor-supply problems have been building for several decades, and they affect all areas of applied nuclear science. It stated that “there is an increasing decline in the percentage of physics Ph.D.s graduating with expertise in nuclear physics at a time when workforce demands are growing” and that “the workforce shortage will become acute unless a coordinated and integrated plan is implemented to build and sustain an

appropriately sized workforce, coupled with the necessary research facilities” (p. 219). Among the report’s recommendations is that fellowships should be established to support postdoctoral researchers interested in the field.

The committee responsible for the report Assuring the U.S. Department of Defense a Strong Science, Technology, Engineering, and Mathematics (STEM) Workforce found that STEM activities in DoD are a small and diminishing part of the nation’s overall science and engineering enterprise. The report presents five principal recommendations for attracting, retaining, and managing highly qualified STEM talent within the department, on the basis of an examination of the current DoD labor force and the defense industrial base. The recommendations include a call for DoD to upgrade education and training for its civilian STEM workforce and to focus investments to ensure that STEM competencies in all potentially critical emerging topical areas are maintained at least at a basic level within the department and its industrial and university bases (NRC, 2012c).

ORGANIZATION OF THIS REPORT

The remainder of this report is divided into five chapters plus three supporting appendixes. Chapter 2 sets the stage for the remaining chapters by providing background on the current directions in radiobiology research. It describes the cancer and noncancer health effects associated with exposure to low doses of radiation and the tools available to researchers to study them. The chapter also outlines the different methods used to analyze biological markers of dose or effect and the factors that influence the risks associated with exposure.

Chapter 3 examines the state of the radiobiology research workforce by first defining the field of study and then summarizing the literature on the supply of and demand for professionals in the discipline. A listing of academic programs in the United States that focus on radiobiology is also presented.

Chapter 4 centers on AFRRI’s organization and its role in radiobiology research. It gives the history of the Institute and describes its infrastructure, staff, budget, and capabilities. This chapter also elucidates AFRRI’s current (2013) research priorities and portfolio; their education, training, and emergency response responsibilities; and their interaction with the broader research community through collaborations and representation in scientific groups.

The concluding chapter of the report, Chapter 5, builds on the foundation of the previous chapters and offers the committee’s primary findings, conclusions, and recommendations. It puts forward a series of proposals for how AFRRI might build on its strengths and advance its mission while

contributing to the body of scientific knowledge on the health effects of exposure to low-dose ionizing radiation.

Agendas of the public meetings held by the committee are provided in Appendix A. Appendix B comprises a brief summary of research programs concerning low-dose ionizing radiation health effects under way in the United States. Biographical information on the committee members and staff responsible for this study are contained in Appendix C.

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