Glossary


Absolute risk:

The excess risk attributed to irradiation and usually expressed as the numeric difference between irradiated and nonirradiated populations (for example, 1 excess case of cancer/1 million people irradiated annually for each rad). Absolute risk may be given on an annual basis or lifetime (70-year) basis.

Absorbed dose:

The energy imparted by ionizing radiation per unit mass of material irradiated. For purposes of radiation protection and assessing risks to human health, the quantity normally calculated is the average absorbed dose in an organ or tissue, equal to the total energy imparted to that organ or tissue divided by the total mass. The SI unit of absorbed dose is the joule per kilogram (J kg−1), and its special name is the gray (Gy). In this report, absorbed dose is given in rads; 1 rad = 0.01 Gy.

Activation:

The production of radionuclides by capture of radiation (for example, neutrons) in atomic nuclei.

Activity:

The rate of transformation (or disintegration or decay) of radioactive material. The SI unit of activity is the reciprocal second (s−1), and its special name is the Becquerel (Bq). In this report, activity is given in curies (Ci); 1 Ci = 3.7 × 1010 Bq.

Activity median aerodynamic diameter (AMAD):

The diameter in an aerodynamic particle size distribution for which the total activities on particles above and below this size are equal. A lognormal distribution of particles sizes usually is assumed.

Acute exposure:

An exposure that took place over a short period of time—hours or days. Acute may also be used to refer to the short-term effects of exposure to radiation.



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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Glossary Absolute risk: The excess risk attributed to irradiation and usually expressed as the numeric difference between irradiated and nonirradiated populations (for example, 1 excess case of cancer/1 million people irradiated annually for each rad). Absolute risk may be given on an annual basis or lifetime (70-year) basis. Absorbed dose: The energy imparted by ionizing radiation per unit mass of material irradiated. For purposes of radiation protection and assessing risks to human health, the quantity normally calculated is the average absorbed dose in an organ or tissue, equal to the total energy imparted to that organ or tissue divided by the total mass. The SI unit of absorbed dose is the joule per kilogram (J kg−1), and its special name is the gray (Gy). In this report, absorbed dose is given in rads; 1 rad = 0.01 Gy. Activation: The production of radionuclides by capture of radiation (for example, neutrons) in atomic nuclei. Activity: The rate of transformation (or disintegration or decay) of radioactive material. The SI unit of activity is the reciprocal second (s−1), and its special name is the Becquerel (Bq). In this report, activity is given in curies (Ci); 1 Ci = 3.7 × 1010 Bq. Activity median aerodynamic diameter (AMAD): The diameter in an aerodynamic particle size distribution for which the total activities on particles above and below this size are equal. A lognormal distribution of particles sizes usually is assumed. Acute exposure: An exposure that took place over a short period of time—hours or days. Acute may also be used to refer to the short-term effects of exposure to radiation.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Aerosol: Extremely small liquid or solid particles suspended in air. Alpha particle: An energetic nucleus of a helium atom, consisting of two protons and two neutrons, that is emitted spontaneously from nuclei in decay of some radionuclides; also called alpha radiation and sometimes shortened to alpha (for example, “alpha-emitting radionuclide”). Alpha particles are weakly penetrating and can be stopped by a sheet of paper or the outer dead layer of skin. Atmospheric testing: Detonation of nuclear weapons or devices in the atmosphere or close to the earth’s surface as part of the nuclear-weapons testing program. Atom: The smallest particle of a chemical element that cannot be divided or broken up by chemical means. An atom consists of a central nucleus of protons and neutrons, and orbital electrons surrounding the nucleus. Atomic bomb: A nuclear weapon that relies on fission only, in contrast with a thermonuclear (“hydrogen”) bomb that uses fission and fusion. Atomic Energy Commission (AEC): The agency of the US government that became the Department of Energy and the Nuclear Regulatory Commission. Attributable risk percent: The percentage of disease that could be eliminated if a particular exposure were stopped. Autoimmune disease: A disease caused by one’s immune system’s attacking the cells of one’s own body rather than attacking foreign cells, such as germs. Autoimmune hypothyroidism: An autoimmune disease that prevents the thyroid from producing enough thyroid hormone. Autoimmune thyroiditis: Damage to the thyroid caused when the body’s immune system attacks and destroys cells in the thyroid. It can be radiation-induced. If the damage is substantial enough, a person may develop signs and symptoms due to hypothyroidism. If there are no signs or symptoms of hypothyroidism, autoimmune thyroiditis is generally not a cause for concern about producing enough thyroid hormone. Background radiation: Ionizing radiation that occurs naturally in the environment, including cosmic radiation; radiation emitted by naturally occurring radionuclides in air, water, soil, and rock; radiation emitted by naturally occurring radionuclides in tissues of humans and other organisms; and radiation emitted by human-made materials containing incidental amounts of naturally occurring radionuclides (such as building materials). Background radiation may also include radiation emitted by residual fallout from nuclear-weapons tests that has been dispersed throughout the world. The average annual effective dose due to natural background radiation in the United States is about 0.1 rem, excluding the dose due to indoor radon, and the average annual effective dose due to indoor radon is about 0.2 rem. Badged dose: An estimate of a person’s external radiation dose, specifically the deep equivalent dose from external exposure to photons, as derived from readings of exposure by one or more film badges assigned to the person.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Basal cells: A cell in the epidermis that give rise to more-specialized cells. Basal-cell carcinoma: A malignant growth originating from basal cells that is most common in fair-skinned or sun-exposed areas; the most common form of skin cancer. Becquerel (Bq): The special name for the SI unit of activity; 1 Bq = 1 disintegration per second. Benign tumor: A general category of tumors that do not invade surrounding tissue. Benign tumors are characterized by slow growth through expansion. They are not malignant or cancerous. Beta particle: An energetic electron emitted spontaneously from the nucleus in decay of some radionuclides and produced by transmutation of a neutron into a proton; also called beta radiation and sometimes shortened to beta (for example, beta-emitting radionuclide). Beta particles are not highly penetrating, and the highest-energy beta radiation can be stopped by a few centimeters of plastic or aluminum. Bias: The systematic tendency of a measurement or prediction of a quantity to overestimate or underestimate the actual value on the average. Biological Effects of Ionizing Radiation (BEIR): A series of National Research Council studies conducted by the committees on the Biological Effects of Ionizing Radiations (BEIR VII is the current study). Biological response: A significant adverse effect in an organism resulting from exposure to a hazardous agent. The determination of whether an effect is significant or adverse sometimes involves subjective judgment. Often called a biologic endpoint or biologic effect in the literature. Cancer: A malignant tumor of potentially unlimited growth that expands locally by invasion and systemically by metastasis. Cancer risk: A theoretical risk of getting cancer if exposed to a substance every day for 70 years (a lifetime exposure). The true risk might be lower. Carcinogen: An agent capable of inducing cancer. Carcinoma: A malignant tumor that occurs in epithelial tissues, which cover the body or body parts and enclose and protect those parts, produce secretions and excretions, and function in absorption. Case-control study: A study that compares exposures of people who have a disease or condition (cases) with people who do not have the disease or condition (controls). Exposures that are more common among the cases may be considered as possible risk factors for the disease. Case study: A medical or epidemiologic evaluation of one person or a small group of people to gather information about specific health conditions and exposures. Cataract: A clouding of the lens of the eye or its capsule that obstructs the passage of light. Central estimate: A “best” estimate of the dose received, as distinct from an upper bound of the dose that accounts for uncertainty in that estimate.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Chance: A situation in which something happens unpredictably without discernable human intention or observable cause. Chronic exposure: An exposure that occurred over a long period of time—weeks, months, or years. Chronic lymphocytic leukemia: A slowly progressing form of leukemia characterized by an increased number of the white blood cells known as lymphocytes that studies have not shown to be caused by radiation in humans. Code of Federal Regulations: Codification of general and permanent rules published in the Federal Register by executive departments and agencies of the federal government and published annually by the US Government Printing Office. Cohort: A group of individuals having a common association or factor. Cohort study: A study involving a group of people who either have or do not have a specified factor, such as exposure to a disease-causing agent. Such studies are usually used to compare disease rates. Committed dose equivalent (CDE): The dose equivalent to organs or tissues of reference that will be received from an intake of radioactive material by a person during the 50-year period after intake. Committed effective dose equivalent (CEDE): The sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent (CDE) to the organs or tissues. It is a measure of the overall risk associated with internal deposition of radioactive material. Computed axial tomography (CAT): A scan that provides three-dimensional x-ray images of some part of the body. It is useful for diagnosing cancer and for planning radiation therapy treatments. Often called a CT scan. Confidence interval: An estimate of the range within which the true value of an uncertain quantity is expected to occur in a specified percentage of measurements or predictions. For example, a 90% confidence interval of (x, y) means that, on the basis of available information, the probability is 0.9 that the true value lies between x and y. Confidence limits: The highest and lowest boundaries in a confidence interval. As used here, a confidence interval accounts for the possibility that different groups of individuals might have different risk estimates even if they have the same range of dose estimates. Because there is uncertainty in risk estimates that are made for different radiation doses, scientists often include a confidence interval with a risk estimate. Confounding factors: Any characteristic that makes it difficult to compare two or more distinct groups in an epidemiologic study. Confounding factors can mask a health effect so that the relationship of the effect and the exposure is not recognized. They can also make it appear as though there is an effect when, in fact, none exists. Correlation: Most generally, the degree to which one phenomenon or variable is associated with or can be predicted from another. In statistics, usually refers to

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program the degree to which a predictive relationship exists between variables. Correlation may be positive (both variables increase or decrease together) or negative or inverse (one variable increases when the other decreases). Curie (Ci): The conventional unit of radioactivity, equal to 3.7 × 1010 Bq. Deterministic effects: Effects that can be related directly to the radiation dose received. The severity increases as the dose increases. A deterministic effect typically has a threshold below which the effect will not occur. Dose: A quantification of exposure to ionizing radiation, especially in humans. Units are rad, mrad, gray, and mgray. Dose equivalent: The measure that indicates the degree of biologic damage caused by radiation. Dose equivalent is measured in rems, mrem, and Sv. Dose rate: The quantity of absorbed dose delivered per unit time. Dose and dose-rate effectiveness factor (DDREF): Dose and dose-rate reduction effectiveness factor, a measure of the extent to which radiation-related damage accruing at a high dose rate is ameliorated when the dose rate or dose is low. This value will presumably vary with the end point measured, but it is not known precisely for such end points as incidence of or death from cancer or any of the other effects also seen among the atomic-bomb survivors. DS86: The currently used system of dosimetry to describe the exposure of the survivors of the atomic bombings of Hiroshima and Nagasaki; introduced in 1986. Dose reconstruction: A scientific activity that estimates doses to people from releases of radioactivity or other pollutants. The reconstruction is usually done by determining how much material was released, how it was transported, and how people came into contact with it and the amount of radiation energy absorbed by their bodies. Dose-response analysis: A statistical analysis to estimate values of parameters that describe the relationship between the dose of a hazardous agent (such as ionizing radiation) and an increase in a specified biologic response (such as a cancer or other health effect) above the normal (background) incidence. In assessing cancer risks in humans posed by exposure to ionizing radiation, for example, linear or linear-quadratic dose-response relationships are used most commonly. Dosimeter: A portable instrument for measuring and registering total accumulated exposure to ionizing radiation. Downwinder: A commonly used term for a person who may have been exposed to fallout due to the US nuclear-weapons testing program. Effective dose: The sum over specified organs or tissues of the equivalent dose in each tissue modified by the tissue weighting factor, as defined in ICRP (1991). Supersedes effective dose equivalent. Effective dose equivalent: The sum over specified organs or tissues of the average dose equivalent in each tissue modified by the tissue weighting factor. Now superseded by effective dose.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Element: A substance that cannot be separated by ordinary chemical methods. Elements are distinguished by the numbers of protons in the nuclei of their atoms. Epidemiologic studies: Studies designed to examine associations—commonly, hypothesized causal relations. They are usually concerned with identifying or measuring the effects of risk factors or exposures. The common types of epidemiologic studies are case-control studies, cohort studies, and cross-sectional studies. Epidemiology: The study of the incidence, distribution, and causes of health conditions and events in populations. Equivalent dose: A quantity obtained by multiplying the absorbed dose by a radiation weighting factor to allow for the different effectiveness of the various types of ionizing radiation in causing late-effect harm in tissue. The equivalent dose is theoretical and has replaced the earlier dose equivalent. The equivalent dose is often expressed in sievert (Sv). It is also sometimes expressed in rem (an older unit). 100 rem = 1 Sv. Estimate: A measure of or statement about the value of a quantity that is known, believed, or suspected to incorporate some degree of error. Etiology: The causes of disease or the study of the causes. Excess absolute risk: The increase in risk of disease posed by exposure to a specified dose, or the arithmetic difference in risk of disease between exposed and unexposed subjects. Usually expressed as increase in risk per unit dose. See Excess relative risk. Excess relative risk: The increase in relative risk of disease posed by exposure to a specified dose. The mathematical distinction between excess absolute risk (calculated by simple subtraction) and excess relative risk is that the latter is calculated by dividing the risk of disease among exposed subjects by the risk among the unexposed and then subtracting 1. Exposure: (A) A general term indicating human contact with ionizing radiation, radionuclides, or other hazardous agents. (B) For the purpose of measuring of ionizing photon radiation, the absolute value of the total charge of ions of one sign produced per unit mass of air when all electrons and positrons liberated or created by photons in air are completely stopped in air. Exposure is the quantity measured, for example, by a film badge. The SI unit of exposure is the coulomb per kilogram (C kg−1). In conventional units used in this report, exposure is given in roentgens (R); 1 R = 2.58 × 10−4 C kg−1. Exposure pathway: The physical course of a radionuclide or other hazardous agent from its source to an exposed person. Exposure route: The means of intake of a radionuclide or other hazardous agent by a person (such as ingestion, inhalation, or absorption through the skin or an open wound). External dose: The dose to organs or tissues of the body due to sources of ionizing radiation located outside the body, including sources deposited on the body surface.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program External exposure: Radiation exposure from a source outside the body. The term refers to radiation, such as gamma rays and x rays, that can penetrate human skin and thus cause biological damage from outside the body. Fallout: Deposition of radioactive particles produced by detonation of a nuclear weapon. Fine-needle aspiration: A procedure in which a fine, hollow needle is inserted into tissue to extract a small amount of tissue for microscopic evaluation. Fractionation of exposure: One of the terms used to describe how an exposure was delivered over time. Exposures can be either single (brief), repeated (fractionated), or continuous (chronic). Gamma rays: Electromagnetic radiation emitted in de-excitation of atomic nuclei, frequently occurring as a result of decay of radionuclides; sometimes shortened to gamma (for example, gamma-emitting radionuclide). High-energy gamma radiation is highly penetrating and requires thick shielding, such as up to 1 m of concrete or a few tens of centimeters of steel. Gastrointestinal tract: Organs of the digestive system, including the esophagus, stomach, small intestine, and upper and lower large intestine (colon). Generalized anxiety disorder (GAD, DSM code 300.02): A relatively common anxiety problem, affecting 5% of the population, that turns daily life into a state of worry, anxiety, and fear. People with GAD experience pathologic anxiety, which is excessive and chronic and typically interferes with the ability to function in normal daily activities. Genetic effect: The result of exposure to radioactivity or substances that cause damage to the genes of a reproductive cell (sperm or egg), which can then be passed from one generation to another. Genetic injury or damage: Harm to a person’s genes that can be passed on to later generations. Germ cells: Reproductive cells—spermatozoa (sperm) in males and ova (eggs) in females. Gonads: Reproductive organs—testes in males and ovaries in females. Graves disease: A form of hyperthyroidism (an over-active thyroid). Goiter: An enlargement of the thyroid gland. Gray: The SI unit of absorbed dose named fo H. L. Gray an English radiation scientist; 1 Gy = 1 J kg−1 = 100 rad. Half-life, biological: The time required for half the quantity of a material taken into the body to be eliminated from the body by biologic processes. For radionuclides, the biological half-time does not include elimination by radioactive decay. Half-life, effective: The time required for the activity of a radioactive substance in the body to decrease to half its value because of the combined effects of biologic elimination and radioactive decay. The effective half-life facilitates evaluating radiation dose from inhaled and ingested radionuclides and applies when the biological and physical half-lives are constant. For an effective half-life of 1 hour, half of the radioactivity would be expected to be

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program eliminated during the first hour. Of the radioactivity that remained, half would be expected to be eliminated during the second hour. That represents one-fourth of the radioactivity initially present. For each successive hour, the expected fractions of the initial radioactivity present that are eliminated would be 1/2, 1/4, 1/8, and so on. This type of decrease over time is called exponential. Half-life, physical: The average time it takes for one-half of any given number of unstable atoms to decay. Half-lives of isotopes range from small fractions of a second to more than a billion years. For example, if on average 100 out of 200 radioactive atoms of a specified kind decay in 1 day (half-life = 1 day), then of the remaining 100 atoms, 50 would be expected to decay during the second day. Similarly, 25 of the remaining 50 atoms would be expected to decay during the third day. This type of decay is called exponential. Half-life, radioactive: See half-life, physical. Hashimoto’s thyroiditis: An autoimmune disease of the thyroid. It is caused by lymphocytes entering the thyroid. The disease causes goiters, tissue damage, and hypothyroidism. Health education: Programs designed with a community to help it know about health risks and how to reduce these risks. Health effect: The result of exposure to substances (such as radiation) that cause any harm to a person’s health. It includes diseases, cancers, birth defects, genetic effects, and death. Health investigation: The collection and evaluation of information about the health of community residents. This information is used to describe or count the occurrence of a disease, symptom, or clinical measure and to evaluate the possible association between the occurrence and exposure to radiation or hazardous substances. Health promotion: The process of enabling people to increase control over, and to improve, their health. High-LET radiation: Radiation with linear energy transfer (LET) values above, say, 10 keV/µm. It produces much damage over a short distance in tissue or other material. In contrast, low-LET radiation produces only a small amount of damage when evaluated over the same amount of deposited energy. Alpha particles represent high-LET radiation. Gamma and x rays are low-LET radiation. It generally takes a larger absorbed dose of low-LET radiation than of high-LET radiation to produce a given amount of damage. Biologic damage produced by low-LET radiation is often more efficiently repaired than damage produced by high-LET radiation. Hodgkin’s disease: A type of lymphoma that appears to originate in a particular lymph node and to spread to the spleen, liver, and bone marrow and is characterized by progressive enlargement of the lymph nodes, spleen, and general lymph tissue.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Hyperparathyroidism: Disorder that is characterized by the excessive production of parathyroid hormones. This results in the body not being able to regulate the concentrations of calcium and phosphorus properly. Hyperthyroidism: A disorder that is characterized by the excessive production of thyroid hormones. Symptoms include nervousness, constant hunger, weight loss, and tremors. Hyperthyroidism is not caused by radiation exposure. Hypothyroidism: A condition caused by too little thyroid hormone in the body. Symptoms include fatigue, weight gain, intolerance to cold, decreased appetite, constipation, hoarseness, menstrual irregularities, dry skin, and hair changes. Immune system disorders: Allergic reactions and disruption of the immune surveillance system whose prime function is to detect and eliminate diseased cells. Incidence: The rate of occurrence of new cases of a specific disease in a specific period, calculated as the number of new cases during a specified period divided by the number of persons at risk of the disease during that period. Ingestion dose pathway: The parts of the food chain or water system that might add to radiation exposure from eating food or drinking water. Internal dose: The dose to organs or tissues due to sources of ionizing radiation in the body. Internal radiation exposure: Exposure from taking a radioactive substance into the body by eating, drinking, or breathing. International Atomic Energy Agency (IAEA): One of the specialized bodies of the United Nations charged with the responsibility of overseeing and setting standards and recommendations for the operation of nuclear activities and for radiation safety in the member states. It is headquartered in Vienna, Austria, and its members have played a major role in the accumulation and dissemination of the information derived from the Chornobyl accident and other accidents involving exposure to ionizing radiation. International Commission on Radiological Protection (ICRP): A nongovernment agency headquartered in Sweden and the United Kingdom, and concerned with radiation protection in the workplace and of the general population. It was founded by the International Congress of Radiology in 1928. It is generally viewed as the world’s leading source of authoritative statements on radiation protection. International Commission on Radiation Units and Measurements (ICRU): A nongovernment agency headquartered in Bethesda, Maryland, and concerned with recommendations regarding harmonized measurement of radiation and responsible for recommending nomenclature for quantities, units and their special names, e.g., Bq, Gy, Sv. International System of Units: A modern version of the meter-kilogram-second-ampere system of units that is published and controlled by the International Bureau of Weights and Measures; also referred to as SI units.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program In utero: Means in the uterus or womb. Iodine-131 (131I): A radioactive isotope of iodine. Iodine is an element required in small amounts for healthy growth and development. It is mainly concentrated in the thyroid gland, where it is needed to synthesize thyroid hormones. 131I is used as a radioactive tracer in nuclear medicine and is found in fallout from nuclear testing. 131I has been demonstrated to cause thyroid cancer in children in moderate and high doses after the Chornobyl accident. Whether very low radiation doses cause thyroid cancer is uncertain. Iodine-131 has a relatively short physical half-life (8 days). Ionizing radiation: Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions. Examples are alpha particles, beta particles, gamma rays or x rays, and cosmic rays. The minimum energy of ionizing radiation is a few electron volts (eV); 1 eV = 1.6 × 10−19 joule (J). Irradiate: To expose to radiation. Isotope: A form of a particular chemical element determined by the number of neutrons in the atomic nucleus. An element may have many stable or unstable (radioactive) isotopes. Latent period: The time after exposure that it takes for a radiation-induced cancer to be manifested. Latent periods, also called latency period, may vary widely between different types of cancer and within subgroups of one type of cancer. Leukemia: The term used to describe a group of malignant, commonly fatal blood diseases characterized by an uncontrolled increase in the number of white cells (generally their immature forms) in the circulating blood. Life Span Study (LSS): Continuing followup of the population exposed to atomic-bomb detonations in Hiroshima and Nagasaki, Japan, and their progeny; conducted by the Radiation Effects Research Foundation (RERF). Linear Energy Transfer (LET): The energy lost by a charged particle per unit distance traversed in a material. The SI unit of LET is joules per meter (J m−1). For purposes of radiation protection, LET normally is specified in water and is given in units of keV µm−1. For low-LET radiations—such as beta particles and the electrons associated with x-rays, gamma rays—little energy is lost in traversing a sheet of paper. For high-LET alpha particles emitted by plutonium isotopes, essentially all the particle’s energy is lost in traversing a sheet of paper. Linear model: The assumption that the effect of exposure to ionizing radiation is directly and simply proportional to dose. Linear non-threshold model (LNT): An empirical equation used to assign risk of cancer induction by a specified genotoxicant (including ionizing radiation). The equation has the form, risk = A + kD, where k is a risk coefficient, D is a measure of dose, and A represents the baseline risk, absent radiation. With this empirical model, any dose in excess of zero is presumed to be associated with an increased risk of cancer. Further, use of this model

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program implies that doubling the dose will double the calculated excess risk. For low radiation doses and dose rates, there are large uncertainties about what the true risks to humans and how they relate to dose. Linear-quadratic model: The assumption that the effect of exposure related not only to the dose received but also to the square of the dose. Lymphocyte: A type of white blood cell that is found primarily in lymph nodes. Lymphocytes provide protection against some kinds of infections. Lymphoma: Malignant tumors originating in cells of lymphatic tissues. Malignancy/malignant neoplasm: A general category of neoplasm that invades surrounding tissue. A malignant tumor is generally characterized by invasive growth and is able to metastasize to distant tissue sites via the lymphatic and blood systems. Malignant: Tending to infiltrate, metastasize, and terminate fatally. Mean: The arithmetic average of a set of values, given by the sum of the values divided by the number of values. The mean of a distribution of values is the weighted average of possible values, each value weighted by its probability of occurrence in the distribution. Median dose: The central estimate in a dose-estimate range. Half the possible doses are above the median; half are below it. A person’s dose is more likely to be near the median than near the low or the high end of the range. Medical monitoring: A program to screen a group of people who are at risk for specific diseases or conditions and to refer individuals for additional evaluation and treatment if needed. Monitoring does not include medical care. Melanoma: A malignant, and often fatal, tumor in cells of the skin that synthesize dark pigments. Metastasis: The spread of cancer through transfer of malignant cells from one organ or part to another part not directly connected with it. Mill tailing: Naturally radioactive residue from the processing of uranium ore into yellowcake in a mill. Although the milling process recovers about 93% of the uranium, the residues, or tailings, contain several radioactive elements, including uranium, thorium, radium, polonium, and radon. Minisatellite: Repeated segments of the same sequence of multiple triplet codons, each segment varying between 14 and 100 base pairs, useful as linkage markers because of their highly polymorphic nature and the fact that they are usually situated near genes. Minisatellites are inherently unstable and susceptible to mutation at a higher rate than other sequences of DNA. Model: A construct (generally mathematical) that attempts to describe the events that underlie some biologic or physical phenomenon of interest, such as the occurrence of cancer after exposure to ionizing radiation. Monte Carlo analysis: The computation of a probability distribution of an output of a model based on repeated calculations using random samplings of the model’s input parameters (variables) from specified probability distributions.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Morbidity: A measure of a diseased condition or state; refers to illness, not death. Morbidity rate: The rate at which people get a disease, usually expressed as the number of cases per 100,000 people per year. Mortality: A measure of the number of people who die from a specific disease or condition. Mortality rate: The rate at which people die from a disease, such as a specific type of cancer, usually expressed as the number of deaths from the disease per 100,000 deaths per year. Multiple myeloma: The proliferation of plasma cells that often replace all other cells within bone marrow, leading to immune deficiency and, frequently, destruction of the outer layer of bone. Mutation: A hereditary change in genetic material; it can be a change in a single gene (point mutation) or a change in chromosome characteristics. National Academy of Sciences (NAS): The National Academy of Sciences is a private, non-profit, self-perpetuating society of distinguished scholars engaged in scientific research. Upon the authority of the charter granted by the Congress in 1863, the NAS has a mandate that requires it to advise the federal government on scientific and technical matters. National Council on Radiation Protection and Measurements (NCRP): A nongovernmental agency based in Bethesda, Maryland, with a charter similar to that of ICRP, but focusing in particular on issues related to radiation protection in the United States. National Research Council (NRC): The principal operating agency of the National Academy of Sciences and the National Academy of Engineering to serve the federal government and other organizations. Neoplasm: Any new or abnormal growth, such as a tumor; neoplastic disease refers to any disease that forms tumors, whether malignant or benign. Neural tube defects: A defect in the neural tube. The neural tube develops into the spinal cord and brain. Defects occur when the neural tube fails to close completely during the early stages of pregnancy. Neutron: An elementary uncharged particle, of mass slightly greater than that of a proton, that is a constituent of atomic nuclei. Nevada Test Site (NTS): The region in Nevada set aside for the continental atmospheric nuclear weapons testing program. Also referred to as the Nevada Proving Ground (NPG). Noble gas: Any of a group of rare gases (helium, neon, argon, krypton, xenon, and radon) that exhibit great stability and very low chemical reaction rates. Nuclear fallout: The descent of airborne particles of dust, debris, and radioactive substances from a nuclear bomb explosion. Millions of curies of radioactivity in the form of dust and debris get carried into the upper atmosphere by the mushroom cloud. Jet stream winds can carry fallout from bomb blasts around the world within a few months.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Nuclear weapon: A weapon that derives its explosive force from nuclear fusion or nuclear fission reactions. Occupational radiation exposure: The radiation exposure of or dose to a person in the course of employment in which individual’s assigned duties involve exposure to radiation and to radioactive materials. Occupational dose does not include dose received from background radiation, from being a patient in medical practice, from voluntary participation in medical research program, or from being a member of the general public. Odds: A measure of the likelihood that an event will occur. For example, the odds of developing a particular disease. Organ dose: The energy absorbed in a specific organ divided by its mass. This quantity is expressed in gray (Gy) or its submultiples. Parathyroid: Any of four small glands next to or on the thyroid gland. The parathyroids secrete a hormone that helps to control the balance between calcium and phosphorus in the body. Photon: A quantum of electromagnetic radiation, having no charge or mass, that exhibits both particle and wave behavior, especially a gamma ray or an x ray. Posttraumatic stress disorder (PTSD, DSM code 309.81): A group of characteristic symptoms that follow exposure to an extreme traumatic stressor involving actual or threatened death or serious injury; another threat to one’s physical integrity; witnessing of an event that involves the death of, injury of, or a threat to the physical integrity of another person; or learning about unexpected or violent death, serious harm, or threat of death or injury experienced by a family member or other close associate. Power: The probability that a study can distinguish between a true exposure-to-disease relationship and a coincidence. The power of a study depends on the size of its population, the amount of radiation exposure, and the number of cases of the disease under investigation. Prevalence: The number of cases of a specific disease existing in a particular population or area at a certain time. Probability: The likelihood (chance) that a specified event will occur. Probability can range from 0, indicating that the event is certain not to occur, to 1, indicating that the event is certain to occur. Probability of causation (PC): The probability that a specific disease in a person was caused by their exposure to a particular hazardous agent (such as ionizing radiation). PC is estimated as a quotient of two risks: PC = R/(R + B), where R is the estimated risk of the disease in a person due to exposure to the particular hazardous agent and B is the estimated background (baseline) risk of the disease in that person from all other causes (that is, the risk in the absence of exposure to that agent). PC differs from risk in that it is conditional on the occurrence of a disease.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Progeny: The decay products resulting after a series of radioactive decay. Progeny can also be radioactive, and decay continues until a stable nuclide is formed. Prospective study: A study in which two groups of people—one exposed and one nonexposed—are followed forward in time (prospective) to determine the possible linkage between exposure and health effects. Public-health activities: Activities conducted to protect, promote, or restore public health. The activities can include such programs and campaigns as surveillance of disease, epidemiologic studies, disease registries, collection of vital statistics, disease-prevention programs, public and provider education, health inspections, and quality-assurance activities. Quadratic model: The assumption that the effect of exposure to ionizing radiation is related to the square of the dose received. Quality factor: A factor that depends on the linear energy transfer by which absorbed doses are multiplied to obtain a quantity that expresses the effectiveness for radiation-protection purposes of an absorbed dose on a common scale for all forms of radiation. Rad: The special name for the conventional unit of absorbed dose; 1 rad = 100 ergs g−1 = 0.01 Gy. Radiation: Energy emitted in the form of waves or particles. See also ionizing radiation. Radiation Effects Research Foundation (RERF): The nonprofit research foundation sponsored by the governments of Japan and the United States that currently supervises the studies of the atomic-bomb survivors; the successor in 1975 of the Atomic Bomb Casualty Commission. Radiation exposure: See exposure. Radiation protection: The control of exposure to ionizing radiation by use of principles, standards, measurements, models, and such other means as restrictions on access to radiation areas or use of radioactive materials, restrictions on releases of radioactive effluents to the environment, and warning signs. Sometimes referred to as radiologic protection. Radioactive: Exhibiting radioactivity. Radioactive decay: The spontaneous transformation of the nucleus of an atom to a state of lower energy. Radioactivity: The property or characteristic of an unstable atomic nucleus to spontaneously transform with the emission of energy in the form of radiation. Radiobiology: A branch of biology that deals with the interaction of biologic systems and radiant energy or radioactive materials. Radioepidemiological tables: A tabulation of estimated probabilities of causation of specific cancers in a person who receives various doses of ionizing radiation. See also Probability of causation and risk. Radiogenic disease: A type of disease assumed on the basis of scientific stud-

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program ies to have an association with radiation exposure. A statement that a cancer is radiogenic does not imply that radiation is the only cause of the cancer but rather that radiation has been shown to be one of its causes. Exposure to other environmental substances could also cause the same type of cancer. Radionuclide: A naturally occurring or artificially produced radioactive element or isotope. Radiophobia: Abnormal fear of radiation. Radiosensitivity: Susceptible to the injurious action of ionizing radiation. Radon: A naturally occurring radioactive gas produced from uranium; decays to form radon progeny. Radon occurs naturally in many minerals and is a chief hazard of uranium mill tailings. Some radon can also be found in homes. Radon decays into other isotopes that emit alpha radiation. Radon progeny: The radioactive products formed in the radioactive decay of radon; radionuclides which when inhaled can expose living cells to their emitted alpha particles. Ratio: A measure of association calculated by dividing one amount by another. Relative biological effectiveness (RBE): A factor used to compare the biological effectiveness of absorbed radiation doses due to different types of ionizing radiation for a defined biologic end point, such as cell killing; this factor is experimentally determined by using x or gamma rays as the standard of comparison. Thus, if 1 Gy of fast neutrons produced the same amount of cell killing as 5 Gy of gamma rays, the RBE of neutrons for cell killing would be 5. The RBE varies with the biologic end point used. Relative risk: The ratio of the risk in one population to that in another. Relative risk indicates the increased or decreased degree of risk among exposed people compared with nonexposed people. A relative risk of 1 indicates no association between the exposure and the disease. A relative risk of 2 indicates that the exposed group is twice as likely as the nonexposed group to experience the health effect being studied. Rem: The special name for the conventional unit of equivalent dose; 1 rem = 100 ergs g−1 = 0.01 Sv = 10 mSv. For gamma and beta radiation and x rays, 1 rem = 1 rad = 0.01 Gy = 10 mGy. Risk: The probability of an adverse event. In regard to adverse effects of ionizing radiation on humans, the term usually refers to the probability that a given radiation dose to a person will produce a health effect (such as cancer) or the frequency of health effects produced by given radiation doses to a specified population within a specified period. The risk of cancer due to a given radiation dose generally depends on the cancer type, sex, age at exposure, and time since exposure (attained age), and it may depend on dose rate. Risk factor: An aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or inherited characteristic that is known from scientific evidence to be associated with a health effect.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Roentgen: The special name for the conventional unit of exposure; 1 R = 2.58 × 10−4 coulomb per kilogram (C kg−1). Sample size: The number of participants in a research study. The larger the sample size in a research study, the more power the study has to detect an association between exposure and a health effect. Screening: The application of a test to detect a potential disease or condition in a person who has no known signs or symptoms of the disease or condition. Sievert: The SI unit of equivalent dose named for R. M. Sievert a Swedish radiophysicists; 1 Sv = 1 J kg−1 = 100 rem. SI units: See International System of Units. Somatic effects: The effects of radiation exposure that result from damage to nonreproductive cells. If the number of cells that suffer somatic effects is great enough, then the damage becomes clinically observable. Squamous cell carcinoma: A malignant growth originating from plate-like cells found in the outer layer of the skin and usually occurring on the skin, lips, inside of the mouth, throat, or esophagus. Standardized incidence ratio (SIR): The ratio of the number of observed cases divided by the number of expected cases. The word standardized means that there has been adjustment for one or more potential bias factors such as age and sex. Standardized mortality ratio (SMR): The ratio of the number of deaths observed in a study population to the number of deaths expected if that population had death rates equivalent to those in some standard, general population (such as the US population). SMRs are typically calculated by using general population rates broken down by intervals of age and calendar time, and by age and race. Statistical significance: The likelihood that an association between exposure and disease risk that a study finds did not occur by chance alone. Statistics: A branch of mathematics dealing with the collection, analysis, interpretation, and presentation of numerical data. Stochastic effect: An effect that occurs on a random basis independent of the size of dose. The effect typically has no threshold and is based on probabilities, with the chances of occurrence of the effect increasing with dose. Cancer is a stochastic effect. Surveillance, Epidemiology, and End Results (SEER): Program developed as a result of the National Cancer Act of 1971, which mandated the collection, analysis, and dissemination of all data useful in the prevention, diagnosis, and treatment of cancer. It is a continuing project of the National Cancer Institute to collect cancer data routinely basis from designated population-based cancer registries in various areas of the country. Thyroid-antibody test: A blood test that measures antibodies against the patient’s thyroid tissue. Thyroid burden: The total activity of a radionuclide in the thyroid.

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program Thyroid dose: The amount (or an estimate of the amount) of radiation, or energy, absorbed by the thyroid gland. Thyroid gland: A two-lobed gland lying at the base of the throat that produces hormones essential for a variety of metabolic processes in the body. It secretes hormones that control body growth and metabolism. When iodine is ingested, much of it goes to the thyroid gland. Thyroid nodules: Lumps in the thyroid gland that may be benign or cancerous. “Cold nodules” are non-functioning lumps in the thyroid gland. “Hot nodules” are overactive thyroid lumps. When a nodule is detected, it is important to diagnose the disease that has caused it. Benign thyroid tumors are often referred to as nodules. Thyroid palpation: The procedure in which a physician characterizes the size, shape, and texture of the thyroid gland by manual examination of the neck. Total effective dose equivalent (TEDE): The sum of the deep dose equivalent (DDE) for external exposures and the committed effective dose equivalent (CEDE) for internal exposures. Tumor registry: A collection of records on the tumors that have been treated at a particular hospital or within a geographic area. Uncertainty: The lack of sureness or confidence in results of measurements or predictions of quantities owing to stochastic variation or to a lack of knowledge founded on an incomplete characterization, understanding, or measurement of a system. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR): One of the specialized bodies of the United Nations charged with the responsibility of evaluating the effects of exposure to atomic (ionizing) radiation on behalf of the member nations. Uranium (U): A radioactive element with atomic number 92 and, as found in natural ores, an average atomic weight of about 238. The two principal natural isotopes are 235U (0.7% of natural uranium), which is fissionable, and 238U (99.3% of natural uranium), which is fertile. Natural uranium also includes a minute amount of 234U. Variability: The variation of a property or quantity among members of a population. Variability is often assumed to be random and can be represented by a probability distribution. Weighting factor (wT): For an organ or tissue (T), the proportion of the risk of stochastic effects resulting from irradiation of the organ or tissue to the total risk of stochastic effects when the whole body is irradiated uniformly. Whole body: For purposes of estimating radiation dose, especially from external exposure, the head, trunk (including male gonads), arms above the elbow, and legs above the knee. Working level (WL): Any combination of the short-lived progeny of radon in 1 liter of air, under ambient temperature and pressure, that results in the ultimate emission of 1.3 × 105 MeV of alpha-particle energy. It is approximately the

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Assessment of the Scientific Information for the Radiation Exposure Screening and Education Program total amount of energy released over a long period by the short-lived progeny in equilibrium with 100 pCi of radon. 1 WL = 2.08 × 10−5 J m−3. Working level month (WLM): A cumulative exposure equivalent to 1 working level for 1 working month (170 hours). 1 WLM = 2.08 × 10−5 J h m−3 × 170 h = 3.5 × 10−3 J h m−3. X radiation: (A) Electromagnetic radiation emitted in de-excitation of bound atomic electrons, frequently occurring in decay of radionuclides, referred to as characteristic x rays, or (B) electromagnetic radiation produced in deceleration of energetic charged particles (such as beta radiation) in passing through matter, referred to as continuous x rays or bremsstrahlung; also called x rays.