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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident EXECUTIVE SUMMARY This report responds to the congressional mandate of Public Law 107-188, Section 127. To satisfy the requirement of this law, the Centers for Disease Control and Prevention (CDC) asked the National Research Council to assess strategies for the distribution and administration of potassium iodide (KI) in the event of a nuclear incident, taking into account projected benefits and harms and the populations that should be included in such a program, and to recommend studies that will improve the base of knowledge on which to make related public-health decisions. The Research Council’s Board on Radiation Effects Research assembled a committee of experts representing an array of relevant disciplines to address the issues related to the distribution of KI. The committee was asked to consider the issues and make recommendations on the basis of scientific knowledge and principles. The task set before the committee is described in the following scope of work. On the basis of its assessment, the committee was to make recommendations to the President of the United States and Congress within 9 months after the start of the study regarding
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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident the projected benefits and harms of a KI distribution program as part of a nuclear incident preparedness program; the most effective and safe way to distribute and administer KI on a mass scale to prevent radiation effects; the populations that should be included in the KI distribution program; the appropriate roles for local, state and federal agencies related to KI distribution in such a preparedness program; and any additional issues that need to be researched, resolved, or addressed. To understand the context of the statement of task presented above, the committee believed that it was important to provide background information on the effects of radioactive iodine and KI on the thyroid gland and to explore various options for using KI to protect the thyroid. In this report, we describe the benefits of and risks posed by KI administration to different population groups and focus particularly on protecting children, the most vulnerable group (tasks a and c); identify alternatives for KI distribution that have been chosen to be best in different parts of the United States and in other countries and recommend a procedure for a local area to evaluate different distribution plans on the basis of site-specific characteristics (task b) and current roles played by local, state, and federal agencies regarding KI distribution (task d); make some recommendations regarding the level at which decisions should be made (state and local level), programs should be funded (federal level), and supplemental stockpiles should be maintained and adequate KI supply (in suitable dosages) ensured (federal level); and identify additional issues that need to be researched or addressed (task e). Radioactive iodines (radioiodines, such as 131I) are produced during the operation of nuclear power plants (NPPs) and during the detonation of nuclear weapons. Radioiodine is one of the contaminants that could be released into the environment in the event of a nuclear incident that involves a disruption of the integrity of the fuel assembly and containment structures of a NPP, because of an
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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident accident or terrorist activity. Exposure to 131I (and other radioisotopes of iodine) by inhalation of contaminated air or ingestion of contaminated food or milk can lead to radiation injury to the thyroid, including increased risk of thyroid cancer and other thyroid diseases, because the thyroid gland concentrates and stores iodine from the blood. For example, the 1986 nuclear accident in Chornobyl exposed many people to 131I, and reports of radiation epidemiology studies indicate that that exposure caused excess cases of thyroid cancer years later in the exposed susceptible population. The Chornobyl experience is discussed in this report because it shows the consequences of exposure in a qualitative sense, even though it is not as relevant for determining quantitatively the risk of such an event in the United States in light of substantial safety and other facility design features in US reactors. Nevertheless, nuclear power plants in the United States contain a source of radioactive iodine that in the event of a very severe incident might impose risks of exposure, which could lead to thyroid cancers. Given that KI is effective in protecting against potential thyroid cancer, KI distribution plans should be considered. The detonation of a nuclear weapon would lead to release of radioiodine, but radioiodine would not be a primary concern compared to the principal thermal and blast effects and the large amount of radiation and non-iodine radioactive materials that would be released. Radiation incidents may be unintentional, as in NPP accidents, or intentional, as in terrorist attacks that damage NPPs or explode "dirty bombs" or nuclear weapons. In the event of an accidental or intentional release of radioactive iodine into the environment, radiation doses1 to the thyroid from radioiodine can be limited by 1 To eliminate confusion over the use of the word dose which is often used to describe both the radiation absorbed dose, expressed in Gray, and the medically administered dose, often expressed in grams or milligrams—the committee has chosen to use the term dose when indicating the radiation absorbed dose and the term dosage when referring to the amount of a drug administered. To eliminate confusion due to the various ways that radiation doses are expressed in the literature, the committee decided to limit its usage to the SI unit for radiation absorbed dose, the Gray (Gy) when possible. For informational purposes SI units are followed in brackets by their equivalent in terms of the older English units. For units presented in the literature in terms of dose equivalent and effective dose equivalent, Sievert (Sv) and rem, the committee converted these doses to the absorbed dose units of Gray and rad when possible. To eliminate confusion over the use of the term “dose” and “exposure” for the radiation absorbed dose to the thyroid gland, the committee chose to use only the term thyroid dose.
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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident appropriate administration of stable iodine such as KI. The nonradioactive iodine in KI is readily taken up by the thyroid gland, thereby competing with and effectively blocking thyroid uptake of radioactive iodine. KI tablets are readily available, are inexpensive, and have a long shelf-life if the tablets are stored in a package designed to prevent exposure to light and moisture. Although the iodate chemical form is used in some European countries and is also stable, it has traditionally not been used as a blocking agent in the United States and is not as readily available. KI tablets are the only form of iodine approved by the US Food and Drug Administration (FDA) for use as a blocking agent. To be most effective, KI must be taken within a few hours before or after exposure to radioiodine. KI does not protect other organs or tissues from external exposure to radiation or from internal exposure to other radioactive isotopes, such as strontium, cesium, and cobalt. It is assumed throughout this report that the need for administration of KI is necessary only once to protect the thyroid gland against inhalation of radioiodine from a passing plume (cloud) and that further protection from radioiodine will be accomplished by evacuation and control of contaminated milk and other foods. Epidemiological studies have shown that fetuses, infants, children, and pregnant and lactating women are most in need of protection from radioiodine exposure. Children are most likely to benefit from KI prophylaxis. Radioiodine can cross the placenta and enter the fetal thyroid. Lactating women can concentrate radioiodine in their milk and transfer it to their nursing infants. Infants and children are more vulnerable to the potentially harmful effects of radioiodine than are adults because their thyroids concentrate iodine more actively on an organ-weight basis and because their thyroids are biologically more radiosensitive.2 For its report, the committee concentrated on three main subjects for assessing the five issues posed in the statement of task: benefits of and risks posed by potassium iodide distribution, 2 The thyroids of fetuses, infants, and children are more susceptible to the effects of ionizing radiation in part because the glands are growing rapidly (especially during the third trimester of gestation and during the first 5 years of life) and have more cell division and higher metabolic activity.
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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident implementation issues related to potassium iodide distribution and stockpile programs, and additional research needed. Benefits of and Risks Posed by Potassium Iodide Distribution On the basis of its assessment, the committee reached the following conclusions and offers a number of recommendations. Conclusions Exposure of susceptible populations to radioiodine from a radiation incident increases the risk of thyroid cancer and other thyroid disorders. Potassium iodide is an important agent for protection against thyroid-related health effects of exposure to radioiodine, if taken shortly before or after exposure. In planning for responses to nuclear incidents in the United States, the likelihood and possible magnitude and extent of a release in the United States cannot be extrapolated from the Chornobyl accident, because of substantial safety and other facility-design features in US reactors. Recommendations KI should be available to everyone at risk of significant health consequences from accumulation of radioiodine in the thyroid in the event of a radiological incident. KI should be available to infants, children, and pregnant and lactating women. There is little benefit in providing KI to adults over 40 years old. To be most effective, KI must be taken within a few hours before or after exposure to inhaled or ingested radioiodine. KI distribution should be included in the planning for comprehensive radiological incident response programs for nuclear power plants. KI distribution programs should consider pre-distribution, local stockpiling outside the
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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident emergency planning zone (EPZ), and national stockpiles and distribution capacity. The FDA should re-evaluate current dosing recommendations and consider extending the shelf-life of KI tablets stockpiled or distributed for use in response to a radiological incident involving radioiodine. Implementation Issues Related to Potassium Iodide Distribution and Stockpile Programs On the basis of its assessment, the committee reached the following conclusion and offers a number of recommendations regarding potassium iodide distribution programs. Conclusion A strategy is needed whereby local planning agencies could develop geographic boundaries for a KI distribution plan based on site-specific considerations because conditions and states vary so much that no single best solution exists. Recommendations A better understanding of the strengths and weaknesses, short-term and long-term successes and failures, and resource requirements of different KI distribution plans implemented in the United States and abroad would be extremely helpful for designing and implementing effective future KI distribution programs. State and local authorities should make the decision regarding implementation and structure of a KI distribution program. The choice of program should be based on how well specific plans would perform on decision objectives, given features of the local region. The decision regarding the geographical area to be covered in a KI distribution program should be based on
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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident risk estimates derived from calculations of site-specific averted thyroid doses for the most vulnerable populations. KI distribution and administration plans developed at the state and local level should receive federal resources for implementation and maintenance. The federal government should maintain stockpiles and a distribution system as a supplement to states’ programs to ensure availability of KI to affected populations in the event of a major radiological incident involving radioiodine. The federal government should ensure an adequate supply of KI tablets in suitable dosages for use by the target populations of infants, children, adults under 40 years old, and pregnant and lactating women of all ages. Additional Research Needed On the basis of its assessment of the current state of information regarding KI distribution programs, the committee reached the following conclusion and offers a number of recommendations for further studies that will improve the base of knowledge on which to make related public-health decisions. Conclusion Although questions remain regarding long-term health risks from radioiodine, particularly among potentially high-risk subgroups, there is now sufficient medical and scientific literature to estimate dose-related thyroid cancer risks following exposure to radioactive iodine. Recommendations KI distribution plans should include a carefully developed and tested public-education program with continuing evaluation to ensure effectiveness and continued access to KI by the appropriate populations.
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Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident A national program should be developed for follow-up of all individuals to whom KI was administered following a radiological incident, to assess short- and long-term health effects of KI administration. Research is needed in a number of areas, as discussed in chapter 8, to provide better information to inform policy-makers and health-care providers about the risks posed by radioiodine exposure and methods to minimize long-term health effects. An evaluation of the strengths and weaknesses, successes and failures (short-term and long-term), and resource requirements of the different KI distribution plans implemented in the US and abroad should be conducted by a federal agency to aid states and local regions in designing and implementing effective KI distribution programs.
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