Cover Image

HARDBACK
$54.00



View/Hide Left Panel

34 Ionizing Radiation

Environmental ALERT…

Everyone is exposed to ionizing radiation. Approximately 82% of this exposure is natural background from cosmic and terrestrial sources, and 18% is due to man-made sources.

Public exposure to ionizing radiation or contamination of the environment by radioactivity engenders intense fear. The emotional and psychologic stresses resulting from exposure should be recognized and addressed early in a radiation incident.

Health care providers should understand the physics, chemistry, and biology of radiation to communicate effectively about it.

This monograph is one in a series of self-instructional publications designed to increase the primary care provider’s knowledge of hazardous substances in the environment and to aid in the evaluation of potentially exposed patients. See page 35 for more information about continuing medical education credits and continuing education units.

Guest Technical Editor:

Niel Wald, MD

Peer Reviewers:

John Ambre, MD, PhD; Charles Becker, MD; Jonathan Borak, MD;

Joseph Cannella, MD; Alan Ducatman, MD; Alan Hall, MD;

Richard J.Jackson, MD, MPH; Howard Kipen, MD, MPH;

Harrison McCandless, MD; Jonathan Rodnick, MD;

Jerry C.Rosen, MS, CHP; Gregg Wilkinson, PhD

U.S. DEPARTMENT OF HEALTH & HUMAN SERVICES

Public Health Service

Agency for Toxic Substances and Disease Registry



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education 34 Ionizing Radiation Environmental ALERT… Everyone is exposed to ionizing radiation. Approximately 82% of this exposure is natural background from cosmic and terrestrial sources, and 18% is due to man-made sources. Public exposure to ionizing radiation or contamination of the environment by radioactivity engenders intense fear. The emotional and psychologic stresses resulting from exposure should be recognized and addressed early in a radiation incident. Health care providers should understand the physics, chemistry, and biology of radiation to communicate effectively about it. This monograph is one in a series of self-instructional publications designed to increase the primary care provider’s knowledge of hazardous substances in the environment and to aid in the evaluation of potentially exposed patients. See page 35 for more information about continuing medical education credits and continuing education units. Guest Technical Editor: Niel Wald, MD Peer Reviewers: John Ambre, MD, PhD; Charles Becker, MD; Jonathan Borak, MD; Joseph Cannella, MD; Alan Ducatman, MD; Alan Hall, MD; Richard J.Jackson, MD, MPH; Howard Kipen, MD, MPH; Harrison McCandless, MD; Jonathan Rodnick, MD; Jerry C.Rosen, MS, CHP; Gregg Wilkinson, PhD U.S. DEPARTMENT OF HEALTH & HUMAN SERVICES Public Health Service Agency for Toxic Substances and Disease Registry

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Case Study Radiation contamination caused by a transportation accident You are a physician on duty in the emergency department of a hospital in a community of approximately 40,000 residents. At 7:45 A.M. you receive notification of a vehicular accident about 4 miles northeast of the city. A truck carrying radioactive material struck a guard rail and rolled 200 feet down an embankment. The truck, which came to rest at a point about 15 feet from the river bank, is on fire. The driver of the truck has minor burns on his hands and a deep laceration of the scalp; he is conscious but somewhat confused and incoherent. His assistant, a passenger in the truck, has second-degree burns on his hands and a simple fracture of his lower left leg. A member of the highway patrol, who was first on scene and noticed the radioactivity placard on the truck, contacted a health physicist from the regional office of the Department of Energy. The health physicist found that the driver of the truck and his assistant are externally contaminated with the radioactive material, which is emitting beta and gamma radiation. The health physicist also detected radioactive contamination along the truck’s path as it rolled down the embankment. Three ruptured containers of radioactive material were found near the truck; it is believed that their contents may have entered the river. The community you serve relies on the river for drinking water, as well as for recreational activities. State police have rerouted traffic and placed road blocks at all points within a 3-mile radius of the accident. However, a young boy whose family is vacationing on a houseboat about 20 yards from the site where the truck came to rest, is known to have approached the scene immediately after the accident occurred. The highway patrol is attempting to locate the boy. (a) Where could you obtain consultation on treatment and management of persons contaminated with radioactivity? _________________________________________________________________ (b) Describe appropriate initial management of the driver and his assistant. _________________________________________________________________ (c) Is the young boy who has not been located in danger? Explain. Are the other occupants of the houseboat at risk as a result of the accident? _________________________________________________________________ (d) If the radioactive material entered the river and consisted of aqueous potassium iodide, what steps could be taken to protect the residents of your community who rely on the river for drinking water? Would these steps differ if the radioactive waste consisted of cesium-137 in solution? _________________________________________________________________ Answers to the Pretest can be found on pages 31–32.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Introduction ❑ Radiation is of two types: ionizing and nonionizing. ❑ The nature of ionizing radiation is participate (e.g., alpha or beta radiation) or wave-like (e.g., X or gamma radiation). The nuclear reactor accidents at Three Mile Island in Pennsylvania in 1979 and at Chernobyl in the USSR in 1986 have increased the public’s concern about exposure to radiation. Awareness of the potential health effects of elevated levels of radon in homes has intensified that concern. The purpose of this document is to help clinicians answer patients’ questions about the early and long-term effects of radiation exposure, the risks of radiation in diagnostic and therapeutic medical procedures, and the potential dangers of radiation to the fetus and future generations. Events just before the turn of the century, which included Roentgen’s discovery of X rays and Becquerel’s recognition of natural radioactivity, allowed us to understand how radiation is produced and how it interacts with matter. Radiation may be of two types, ionizing or nonionizing (Figure 1). Ionizing radiation is capable of physically disrupting neutral atoms by dislodging orbital electrons, thus forming an ion pair consisting of the dislodged electron and the residual atom. Ion pairs are chemically reactive and may produce toxic agents in the cell (e.g., free radicals from water), which can interfere with normal life processes. Nonionizing radiation, on the other hand, does not dislodge orbital electrons or destroy the physical integrity of an impacted atom. The health effects of nonionizing radiation are not addressed in this document. Figure 1. Types of Radiation Adapted from: Leach-Marshall JM. Analysis of radiation detected from exposed process elements from the krypton-85 fine leak testing system, page 50. Semiconductor Safety Association Journal 1991;5(2):48–60.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Ionizing radiation exists as either particles or electromagnetic waves. Particulate radiation (e.g., alpha particles, beta particles, neutrons, and protons) has finite mass and may or may not carry a charge. Electromagnetic radiation, on the other hand, has no mass or charge; it consists of electric and magnetic forces that move at the speed of light in consistent patterns of various wavelengths. The continuum of wavelengths constitutes the electromagnetic spectrum. The shorter wavelengths—gamma radiation and X radiation—have high energies, and like particulate radiation, are capable of ionizing matter. The longer wavelengths of the electromagnetic spectrum, which include radio waves; microwaves; and infrared, visible, and ultraviolet radiation have relatively low energies and are nonionizing. Not all forms of ionizing radiation have the same biologic effects. Generally speaking, for directly ionizing particles, the ion density along the path of low-energy radiation is greater than that along the path of high-energy radiation; low-energy radiation moves slower and has more time to interact. However, the total pathway of low-energy radiation is usually shorter, so the total number of interactions may well be less than with high-energy radiation. Similarly, the ion density toward the end of the radiation path is greater than at the beginning because the velocity of the radiation is less and the probability of interaction is greater. Alpha particles are capable of producing the highest specific ionization (i.e., greatest number of ion pairs per unit length of path), followed in order by beta particles and electrons. X radiation and gamma radiation interact with matter by transferring energy to electrons. (For more information, see Appendix I, Forms of Ionizing Radiation.) The units that have evolved to measure ionizing radiation are the result of its many facets. Radiation units (Table 1) may characterize the (1) energy, (2) radioactive decay rate, (3) effect in air, (4) ability to be absorbed by matter, or (5) biologic effect. Units may be modified by prefixes such as milli (indicating thousandths of the base unit), micro (millionths), pico (billionths), kilo (a thousand times), or mega (a million times). The units used most commonly in this document are rad (radiation absorbed dose) and rem (roentgen equivalent in man or mammal). The rad describes the dose of radiation in terms of the amount of energy absorbed by a given mass, for example, of water or tissue. The absorption of 100 ergs of ionization energy in 1 gram of water has a value of 1 rad. Use of the rem takes into account the biologic effectiveness of the various types of radiation. The rem is numerically equal to the rad multiplied by a Radiation Weighting Factor (formerly “quality factor”). The Radiation Weighting Factor (RWF) reflects differences in the amount of each type of radiation necessary to produce the same biologic effect. For beta, gamma, and X radiation, RWF is 1.0, making their effect on tissue equivalent. The RWF for alpha particles is 20, indicating its biologic effect is 20 times greater than the effect of beta, gamma, or X radiation.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Table 1. Units of radiation measurement Characteristic Unit Description Energy electron volt (eV) (also ergs, joule) Kinetic energy of an electron as it moves through a potential difference of 1 volt. Rate of radioactive decay curie (Ci) Radioactivity emitted per unit of time (1 Ci=3.7×1010 disintegrations per second). Air exposure roentgen (R) Amount of X and gamma radiation that causes ionization in air. One roentgen of exposure will produce about 2 billion ion pairs per cubic centimeter of air. Absorbed dose rad Dose resulting from one roentgen of ionizing radiation deposited in any medium, typically water or tissue. One rad results in the absorption of 100 ergs of ionizing radiation per gram of medium. Biologic effectiveness rem Dose of any form of ionizing radiation that produces the same biological effect as 1 roentgen; 1 rem=1 rad x Radiation Weighting Factor (RWF), where the value of RWF depends on the type of radiation as follows: X radiation=1.0 gamma radiation=1.0 beta=1.0 alpha=20 neutrons=5 to 20, depending on their energy A new System Internationale (SI) nomenclature has been adopted, which is used by international, as well as many domestic, professional organizations and journals (Table 2). Table 2. Equivalency of international units Unit Symbol Equivalency Gray Gy 1 Gy=100 rad Sievert Sv 1 Sv=100 rem Becquerel Bq 1 Bq=2.7×10−11 Ci (or 1.0 disintegration per second)

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education (1) A health physicist from the state health department calculates that the young boy at the scene of the accident in the case study potentially received a maximum radiation dose of so millirads (mrad). Express this dose in millirems (mrem) and Sieverts (Sv). _________________________________________________________________ _________________________________________________________________ (2) What dose of X radiation would produce the same biologic effect as so mrad of gamma or beta radiation? If the radioactive material in the case study had been an alpha-emitter instead of a beta and gamma emitter, would the biologic effects be greater? Explain. _________________________________________________________________ _________________________________________________________________ Exposure Pathways ❑ Our environment includes continual irradiation from both cosmic and terrestrial sources; this natural radiation background is significantly affected by altitude and geology. ❑ In addition to natural background, an individual’s radiation exposure can be increased by factors such as lifestyle (e.g., smoking), geography (e.g., location of residence) and health requirements (e.g., medical diagnosis and therapy). Humans receive an average radiation dose of 300 to 450 mrems per year from both natural (about 82%) and man-made (about 18%) sources. Natural radiation background (Figure 2) is from terrestrial sources and from high-energy particles emanating from stars (including our sun) and other bodies in outer space. Cosmic radiation consists mostly of protons (about 90%), with the remainder being alpha particles, neutrons, and electrons; only about 1/1000 of cosmic radiation penetrates to the earth’s surface. Near sea level, cosmic radiation results in an average dose of ionizing radiation to U.S. residents of about 30 mrem/year. At higher elevations, such as in the Rocky Mountains, where there is less atmosphere to act as a shield, exposures due to cosmic radiation increase by a factor of about two. An even greater increase is experienced during high-altitude air travel; however, passengers of commercial flights are airborne at high altitudes for only a few hours at a time and do not receive significant exposures from this source.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Figure 2. Sources of ionizing radiation exposure for the U.S. population (Average annual effective equivalent dose) Adapted with permission from Health effects of exposure to low levels of ionizing radiation: BEIR V. Copyright 1988 by the National Academy of Sciences. Courtesy of the National Academy Press, Washington, DC. Terrestrial radiation comes from radioactive elements (radionuclides) that were present at the time the earth was formed, and that continue to decay, forming additional radionuclides in the process. Unusual soil composition has increased background radiation twenty-fivefold or more in a few areas in the world. Locations with high background due to naturally occurring radioactive elements in the soil, most of which are derived from the decay of uranium, include the Rocky Mountains (100 mrem/year); Kerala, India (1300 mrem/year); coastal regions of Brazil (500 mrem/year); granite rock areas of France (265 mrem/year); and the northern Nile Delta (350 mrem/year). In the United States, the lowest radiation dose rates are attributed to the sandy soils of the Atlantic and Gulf coastal plains. One of the products formed during the decay of uranium is radon-222, an alpha-emitting radionuclide. Radon-222 contributes an average equivalent whole-body dose of about 200 mrem/year. Studies of uranium miners and other populations have indicated that inhalation of radon-222 increases the risk of lung cancer, especially in smokers. (See Case Studies in Environmental Medicine: Radon Toxicity.) Residents of homes built on abandoned uranium mine and mill tailings or near uranium mines, such as in the Southwest United States (e.g., Mesa County, Colorado) or in areas in Czechoslovakia, have increased internal radiation exposure due to inhalation of radon, as well as increased external radiation exposure due to uranium in the soil.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Construction materials such as wood, granite, and brick bring terrestrial radioactive sources into closer proximity. The dose rate that is attributable to the naturally occurring radionuclides in wood frame buildings is typically less than 10 mrem/year; occupants of masonry structures receive a dose rate of about 13 mrem/year. The dose rate varies not only with the material, but also with ventilation, room size, room location within the structure, season of the year, and other factors. Potassium is essential to health, and one of its isotopes, potassium-40, is radioactive. Potassium-40 makes its way into the body through foods (e.g., bananas) and through inhaled fossil-fuel combustion products (e.g., fly-ash particulates). Because potassium deposits in muscle tissue, potassium-40 is widely distributed throughout the body. We receive an annual internal dose to all organs of approximately 18 mrem from this radionuclide. Radiation background from man-made sources includes fallout from aboveground atomic weapon detonations (about 1 mrem/year for U.S. inhabitants), nuclear fuel production and nuclear reactors (less than 1 mrem/year), medical devices (about 50 mrem/year), and various consumer products. Although the United States and the former USSR have stopped aboveground atomic detonations, the dose rate from atomic weapons testing will continue into the next century because of the long-lived isotopes formed during previous tests and the continued aboveground testing carried out by China and France. As of 1990, 113 nuclear power plants were operating in the United States. In addition, 75 nuclear reactors were being used for training and research, while about 70 reactors were operating at U.S. Department of Energy (DOE) facilities, and at least 100 were used to power military submarines, cruisers, and aircraft carriers. Supporting these reactors are mines, mills, processing plants, and storage sites for spent fuel, all of which are potential sources of radiation exposure. The current deposits of radioactive waste generated by production and use of atomic weapons and nuclear power reactors will remain a potential exposure hazard for 10,000 years or more. Radiation exposure incurred for medical reasons can contribute the greatest dose from artificial sources. Worldwide, more than 1 billion medical diagnostic X-ray examinations, more than 300 million dental X-ray examinations, and about 4 million radiation therapy procedures or courses of treatment are performed annually. In the United States, over half of the population is exposed to X radiation each year, and more than half of these are diagnostic procedures, including dental diagnosis. The rest experience X radiation during fluoroscopy, radiation therapy (Table 3), and nuclear medicine (Table 4).

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Table 3. Common diagnostic X-ray doses* Examination Mean KVP Mean MAS (mrem) Testes/ Ovaries (mrem) Embryo/ Fetus Chest (PA) 80 12 <0.5 <0.5 Skull (lateral) 72 50 <0.5 <0.5 Abdomen (KUB, AP) 78 601 13.7/146 150 Retrograde pyelogram (AP) 77 91 17.2/161 170 Thoracic spine (AP) 75 82 <0.5/0.7 0.9 Cervical spine (AP) 69 48 <0.5 <0.5 Lumbosacral spine (AP) 77 112 13.2/145 150 Pelvis (AP) 100 30 83/79 133 Barium enema (AP) 120 20 68/132 140 *KVP=kilovolt peak; MAS=milliampere second; PA=posteroanterior view; AP=anteroposterior view; mrem=millirem; KUB=kidney, ureter, bladder. Reprinted with permission from the August, 1987; volume 36, number 2, issue of American Family Physician, published by the American Academy of Family Physicians. Table 4. Common radionuclides used in nuclear medicine Examination Agent mCi* Whole body (mrem)* Target Organ (mrem) Lung Technetium-99† 3 10 Lung—1000 Lung Xenon-133 gas 15 3 Lung—150 Heart Thallium-201 chloride 1.5 360 Kidney—2200 Heart Technetium-99¶ 15 200 Blood—300 Liver Technetium-99§ 3 60 Liver—1000 Bone Technetium-99** 20 200 Bone—450 Kidney Technetium-99†† 10 233 Kidney—500 *mCi=millicurie, mrem=millirem †Radionuclide delivered in microspheres of human serum albumin ¶Radionuclide incorporated in red blood cells §Radionuclide delivered as sulfur colloid **Radionuclide incorporated in methylene diphosphonate ††Radionuclide incorporated in diethylenetriaminepentaacetic acid (DTPA) Adapted with permission from the August, 1987; volume 36, number 2, issue of American Family Physician, published by the American Academy of Family Physicians. In contrast to environmental exposures, medical procedures usually restrict radiation to local areas. However, during the course of exposing only a small fraction of the body, relatively large doses may be delivered to the bone marrow, which, in comparison to other parts of the body, is very sensitive to radiation. Although the risks due to

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education radiation exposure are small for patients undergoing medical treatments, the cumulative risk to medical and dental personnel who are present is greater. In addition, staff who are not properly protected may receive whole-body, rather than localized, exposures. Procedures that can be used to protect health care personnel include limiting the time of exposure, maintaining an adequate distance between the X-ray beam and personnel, and providing adequate shielding. A number of natural and artificially produced radioactive materials are used in consumer products. Of these, tobacco products probably represent the single greatest radiation hazard to smokers. Tobacco smoke contains polonium-210 and lead-210, alpha-emitting radon decay products. These radionuclides may be deposited and retained on the large, sticky leaves of tobacco plants or may derive from the uranium naturally present in the phosphate fertilizers used on the plants. When the tobacco in a cigarette is lit, the radioactive materials are volatilized and enter the lungs. The bronchial lining of the lungs of a person who smokes 1.5 packs of cigarettes per day may receive as much as 16,000 mrem/year (Table 5). The radiation from tobacco smoke may contribute to the carcinogenicity associated with active and passive cigarette smoking. Although radiation values for dental porcelain and eyeglasses (Table 5) are large, these sources are not a health hazard because the radiation they produce is distributed over a few millionths of an inch in comparatively insensitive tissues; the total contribution of dental porcelain and eyeglasses as an equivalent whole-body dose is less than 5 mrem/year. Table 5. Background radiation from consumer products Product Local Dose (mrem/year) Portion of Body Considered Coal combustion (fly ash) 0.03–0.3 lungs Oil combustion (soot) 1.6 lungs Gas ranges (natural gas) 5 lungs Tobacco products* 16,000 lungs Dentures and crowns† 700 superficial layers of tissue in contact with teeth Ophthalmic glass¶ 4,000 cornea Smoke detectors 0.008 whole body *Dose for cigarette smokers only; does not include doses experienced by those subjected to passive smoke. †Due to the uranium present in glazed dental porcelain. ¶Applies to eyeglasses tinted with uranium or thorium. Adapted from: National Council on Radiation Protection and Measurements (NCRP). Radiation exposure of the U.S. population from consumer products and miscellaneous sources. Bethesda, Maryland: NCRP, 1988. NCRP Report No. 95.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education (3) List at least five potential sources of radiation unrelated to the workplace to which the truck driver in the case study may be exposed. Compare the annual dose from each of these sources. _________________________________________________________________ _________________________________________________________________ Who’s at Risk ❑ Workers in the nuclear energy and defense industries are at greatest risk of exposure to ionizing radiation. ❑ Accidental releases of radiation can occur while producing, using, storing, or transporting radionuclides. ❑ Long-term sequelae of acute high-level or low-level radiation (i.e., cancer and genetic effects) are difficult to assess for a number of reasons. Important data about human effects from exposure to ionizing radiation come from survivors of the atomic bomb detonations in Hiroshima and Nagasaki. Additional evidence comes from inhabitants of the Marshall Islands who experienced fallout from thermo-nuclear testing on Bikini Atoll, radium dial painters, pioneer radiologists, and patients receiving radiation therapy (e.g., patients who were irradiated in the 1950s as treatment for ankylosing spondylitis). Effects of high-level exposure include acute radiation sickness and fatalities. The major long-term health risks of ionizing radiation are cancer, birth abnormalities (from in utero irradiation), infertility, and genetic abnormalities, which are discussed in Physiologic Effects, page 13. Risk of radiation-induced cancer in human populations is difficult to calculate for four reasons: (1) the total number of known radiation-induced cases is too small and the doses too high to allow accurate extrapolation to low doses; (2) cancer from other causes is a prevalent disease (the incidence of cancer morbidity in the U.S. population is 30% to 35%), making incremental incidences due to radiation exposure difficult to detect; (3) radiation-induced cancer cannot be distinguished from cancer due to other causes (although investigators using new molecular biology techniques are attempting to make this distinction possible); and (4) the interval between radiation exposure and cancer appearance may be several decades. Exposure to low-level ionizing radiation occurs mostly in the workplace. Workers at risk are those involved in the following activities: operating nuclear power plants, other nuclear industrial facilities, or nuclear-powered naval vessels; purifying, enriching, and fabricating uranium for nuclear reactor fuel and for weapons production and use; and working at radionuclide storage sites. In addition, medical technicians; researchers; uranium miners and other underground

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Figure 4. Treatment scheme for patients receiving an acute high-dose radiation exposure *Whole-body exposures greater than 4 Gy may require bone marrow transplantation or administration of colony-stimulating factors or other hematopoietic growth factors that stimulate proliferation of hematopoietic stem cells. However, few data exist to support firm recommendations about the use of these treatments for radiation victims. Adapted from: Browne D, Weiss JF, MacVitlie TJ, Pillai MV. Treatment of radiation injuries. New York: Plenum Press, 1990.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education ❑ Treatment of a patient who is internally contaminated is specific to the contaminating radionuclide and chemical form. In radiation accidents, the identity of the radionuclide contaminant and its chemical and physical state must ultimately be determined. Radio-nuclides present at a workplace are usually known, and shipping documents and load manifests detail the hazardous contaminants at transportation accidents. Sometimes it will not be clear whether internal contamination has occurred. Samples collected during external decontamination will provide clues about possible internal contamination. Skin wipes, nasal swabs, urine, and feces should be collected for analysis at a laboratory capable of detecting and identifying radionuclides. Local and whole-body counting can be done at specialized facilities. As mentioned above, gentle mechanical cleansing of wounds and skin and the areas around mouth and nose will prevent further ingestion and absorption of radioactive materials. Chelation with diethylenetriaminepentaacetic acid (DTPA) accelerates the urinary excretion of some transuranic metals (e.g., plutonium, californium, americium, and curium) and some rare earth ions (e.g., cerium, yttrium, lanthanum, promethium, and scandium). DTPA is an investigational drug available from REAC/TS (see Other Sources of Information, page 29). DTPA can be administered intravenously or as an inhaled aerosol according to treatment protocols established by investigators at REAC/TS. In rare cases of massive pulmonary deposition of very hazardous aerosolized radionuclides, lung lavage may be of value. Appendix II is a treatment summary for selected elements. (10) How will you manage and treat the truck driver and his assistant in the case study? Assuming the young boy has experienced no immediate effects from the irradiation, what follow-up is appropriate for him? _________________________________________________________________ Additional information for the case study: An hour after the accident, the concentration of radioactivity at the point where the material entered the river was measured at 20 picoCuries per liter (pCi/L) of river water. The town switched to an alternate source of drinking water. Two weeks later, the state public health department declared the river water safe, and the town resumed using the river as its source of drinking water. (11) You continue to receive calls from your patients, expressing fear and concern about exposure to radioactivity. One of these patients insists that a rash that developed on his arm yesterday is caused by showering with “radioactive water.” A patient who is pregnant fears that her unborn child will be malformed or have cancer as a result of her drinking water from the river. How will you respond? _________________________________________________________________

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Standards and Regulations During the period 1900 to 1930, standards for radiation protection were informal and set quite high (approximately 60 R/year). They reflected concern for acute effects of exposure. When concerns over the long-term effects of radiation exposure began to develop (1930 to 1950), protection standards were formalized. The recommendation in 1934 of the U.S. Advisory Committee on X-Ray and Radium Protection (now the National Council on Radiation Protection and Measurements [NCRP]) was to restrict whole-body exposures to less than 0.1 R/day. From 1950 to 1960, attention centered on genetic effects of radiation exposure, and recommendations were proposed to limit exposure to the equivalent of 5 rem/year, which applied to both the general public and workers. Because any amount of radiation exposure poses some risk, all standards now employ a philosophy that radiation exposures should be limited to levels that are as low as reasonably achievable (ALARA) and consistent with the benefits of radiation to society. Regulatory agencies in the United States that are involved in radiation control include the Nuclear Regulatory Commission, Department of Transportation, Food and Drug Administration, Occupational Safety and Health Administration, and the General Accounting Office. EPA has also established a standard for drinking water of 5 pCi/L, which applies to radioactivity from radium-226 and radium-228 combined. A new drinking water standard of 20 pCi/L each for radium-226 and radium-228 has been proposed. Many states and cities also have regulations concerning the use of and protection from radiation. NCRP, established in 1964 to advise Congress on issues related to radiation, and the International Commission on Radiological Protection (ICRP) recommend the standards in Table 7.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Table 7. Summary of recommendations for ionizing radiation Dose Limits for Workers*     ICRP, 1991† NCRP, 1993¶ Based on stochastic effects§ (e.g., cancer and genetic damage) 5 rem (50 mSv) annual effective dose limit and 10 rem (100 mSv) as 5-year cumulative effective dose limit 5 rem (50 mSv) annual effective dose limit and 1 rem (10 mSv) times age in years cumulative effective dose limit Based on nonstochastic effects§ (e.g., lens cataracts and fertility impairment) 15 rem (150 mSv) equivalent dose limit to lens of eye and 50 rem (500 mSv) annual equivalent dose limit to skin, hands, and feet 15 rem (150 mSv) annual equivalent dose limit to lens of eye and 50 rem (500 mSv) annual equivalent dose limit to skin, hands, and feet Dose Limits for the Public*     ICRP, 1991 NCRP, 1993 Based on stochastic effects 0.1 rem (1 mSv) annual effective dose limit, and, if needed, higher values provided that the annual average over 5 years does not exceed 0.1 rem 0.1 rem (1 mSv) annual effective dose limit for continuous exposure and 0.5 rem (5 mSv) annual dose limit for infrequent exposure Based on nonstochastic effects 1.5 rem (15 mSv) annual equivalent to lens of eye and 5 rem (50 mSv) annual equivalent dose limit to skin, hands, and feet 5 rem (50 mSv) annual equivalent dose limit to lens of eye, skin, and extremities Embryo-fetus 0.2 rem (2 mSv) equivalent dose to the woman’s abdomen once pregnancy has been declared 0.05 rem (0.5 mSv) equivalent dose limit in a month once pregnancy is known *The dose limits for both workers and the public exclude medical and natural background exposures. Note that the dose limits for the public are lower, in general, than those for workers. Workers, by virtue of the ability to work, tend to be a healthier population than the public, which includes susceptible populations, the elderly, and children. †International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Annals of the ICRP 21. Elmsford, New York: Pergamon Press, 1991. ¶National Council on Radiation Protection and Measurements (NCRP). Limitation of exposure to ionizing radiation. Bethesda, Maryland: NCRP, 1993. NCRP Report No. 116. §Stochastic effects are those effects for which the probability of occurrence, rather than the magnitude of the effect, is proportional to dose. Not all irradiated persons show such effects; however, the probability that they will can be described by a dose-response curve that extends to zero with no threshold. Nonstochastic effects are proportional in severity to the magnitude of the absorbed dose; they probably have a threshold below which no effect will be observed because simultaneous injury to many cells is required.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Suggested Reading List Acute High-Level Exposure Finch SC. Acute radiation syndrome. JAMA 1987;258:664–8. Gale RP, Butturini A. Medical response to nuclear and radiation accidents. In: Wilkinson GS, ed. The nuclear energy industry. Occup Med: State Art Rev 1991;6(4):581–96. Hendee WR, Doege TC, Wheater RH, eds. Proceedings of the international conference on non-military radiation emergencies, November 19–21, 1986. Chicago: American Medical Association, 1987. MacLeod GK, Hendee WR, Schwarz MR. Radiation accidents and the role of the physician: a post-Chernobyl perspective. JAMA 1986;256:632–5. Mettler FA, Jr., Moseley, RD, Jr. Medical effects of ionizing radiation. New York: Grune & Stratton, Inc., 1985. Miller AB, Howe GR, Sherman GJ, et al. Mortality from breast cancer after irradiation during fluoroscopic examinations in patients being treated for tuberculosis. N Engl J Med 1989;321:1285–9. Saenger EL. Radiation accidents. Ann Emerg Med 1986;9:1061–6. Schull WJ, Otake M, Neel JV. Genetic effects of the atomic bombs: a reappraisal. Science 1981;213:1220–7. Sever LE. Parental radiation exposure and children’s health: are there effects on the second generation? In: Wilkinson GS, ed. The nuclear energy industry. Occup Med: State Art Rev 1991;6(4):513–28. Upton AC. Hiroshima and Nagasaki: forty years later. Amer J Ind Med 1984;6:75–85. Low-Level Exposure Adelstein SJ. Uncertainty and relative risks of radiation exposure. JAMA 1987;258:655–7. American Medical Association. Health threat with a simple solution. A physician’s guide to radon. Chicago: American Medical Association, 1990. Au WW. Monitoring human populations for effects of radiation and chemical exposures using cytogenetic techniques. In: Wilkinson GS, ed. The nuclear energy industry. Occup Med: State Art Rev 1991;6(4):597–612. Brill AB, Adelstein SJ, Saenger EL, et al. Low-level radiation effects: a fact book. New York: The Society of Nuclear Medicine, 1985. Dohrenwend BP, Dohrenwend BS, Warheit GJ, et al. Stress in the community: a report to the President’s Commission of the accident at Three Mile Island. Ann NY Acad Sci 1981;365:159–74. Hendee WR, ed. Health effects of low-level radiation. East Norwalk, Connecticut: Appleton-Century-Crofts, 1984. Howe GR. Risk of cancer mortality in populations living near nuclear facilities. JAMA 1991;265:1438–9. Jablon S, Hrubek Z, Boice JD, Jr. Cancer in populations living near nuclear facilities. JAMA 1991;265:1403–8. Upton AC, Shore RE, Harley NH. The health effects of low-level ionizing radiation. Annu Rev Publ Health 1992;13:127–50. Samet JM. Indoor radon and lung cancer—estimating the risks. West J Med 1992;156:259. Wilkinson GS. Epidemiologic studies of nuclear and radiation workers: an overview of what is known about health risks posed by the nuclear industry. In: Wilkinson GS, ed. The nuclear energy industry. Occup Med: State Art Rev 1991;6(4):715–24.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Treatment Butturini A, DeSouza PC, Gale RP, et al. Use of recombinant granulocyte-macrophage colony-stimulating factor in the Brazil radiation accident. Lancet 1988;2:471–5. Gale RP. Immediate medical consequences of nuclear accidents: lessons from Chernobyl. JAMA 1987;258:625–8. International Commission on Radiological Protection. Principles for handling emergency and accidental exposures of workers. ICRP Publication 28, Annals of the ICRP vol. 2, number 1. Elmsford, New York: Pergamon Press , 1978. Kastenberg WE. Radiation accidents and nuclear energy: medical consequences and therapy. Ann Intern Med 1988;109:730–44. Ricks RC, Berger ME, O’Hara F, eds. The medical basis for radiation accident preparedness. III: psychological perspective. New York: Elsevier, 1991. Wald N. Diagnosis and therapy of radiation injuries. Bull NY Acad Med 1983;59:1129–38. Wald N. Acute radiation injuries and their medical management. In: Mossman KL, Mills WA, eds. The biological basis of radiation protection practice. Philadelphia: Williams & Wilkins, 1992. Government Publications Jablon S, Hrubec Z, Boice JD, Jr, Stone BJ. Cancer in populations living near nuclear facilities. Bethesda, Maryland: Public Health Service, US Department of Health and Human Services, 1990. NIH publication 90– 874. National Academy of Sciences Advisory Committee of the Biological Effects of Ionizing Radiation (BEIR). Health effects of exposure to low levels of ionizing radiation. Washington, DC: National Academy Press 1972, 1980, 1990. National Academy of Sciences. Medical implications of nuclear war. Washington, DC: National Academy Press, 1986. Other Sources of Information More information on the adverse effects of ionizing radiation and the treatment and management of radiation-exposed persons can be obtained from ATSDR, your state and local health departments, and university medical centers. For clinical consultation and assistance, physicians and other health care providers are urged to contact Radiation Emergency Assistance Center/Training Site (REAC/TS) Telephone: (615)–576–3131 (day); (615) 481–1000 (24-hour hotline) c/o Oak Ridge Institute for Science and Education, P.O. Box 117, Oak Ridge, Tennessee, 37831–0117. Information and assistance may also be obtained from the Nuclear Regulatory Commission (202) 492–7000 and CHEMTREC ([800] 424–9300; 24-hour hotline) or from the offices listed below. The United States Department of Energy (DOE) regional coordinating offices should be notified for radiological assistance as soon as possible. At the request of a patient or the attending physician, a DOE radiologic assistance team physician may give advice regarding hospitalization and further definitive treatment. The physician may also make available special DOE medical facilities for the diagnosis and treatment of radiation injury. DOE’s geographical areas of responsibility are listed below. Through this single contact, the resources of thirteen federal agencies will be made available.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Department of Energy Regional Offices Region 1 (Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont) Brookhaven Area Office (516) 345–2200 Upton, Long Island New York, NY 11973 Region 2 (Arkansas, Kentucky, Louisiana, Mississippi, Missouri, Puerto Rico, Tennessee, Virginia, Virgin Islands, and West Virginia) Oak Ridge Operations Office (615) 576–6833 or (615) 525–7885 PO Box E Oak Ridge, TN 37831 Region 3 (Alabama, Canal Zone, Florida, Georgia, North Carolina, and South Carolina) Savannah River Operations Office (803) 824–6331 , ext. 3333 PO Box A Aiken, SC 29802 Region 4 (Arizona, Kansas, New Mexico, Oklahoma, and Texas) Albuquerque Operations Office (505) 844–4667 PO Box 5400 Albuquerque, NM 87115 Region 5 (Illinois, Indiana, Iowa, Michigan, Minnesota, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin) Chicago Operations Office (312) 972–5731 or (312) 972–4800 9800 S Cass Avenue Argonne, IL 60439 Region 6 (Colorado, Idaho, Montana, Utah, and Wyoming) Idaho Operations Office (208) 526–1515 PO Box 2108 Idaho Falls, ID 83401 Region 7 (California, Hawaii, and Nevada) San Francisco Operations Office (510) 273–4237 333 Broadway Oakland, CA 94612 Region 8 (Alaska, Oregon, and Washington) Richland Operations Office (509) 842–7381 PO Box 550 Richland, WA 99352

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Answers to Pretest and Challenge Questions Pretest questions are on page 1. Challenge questions begin on page 5. Pretest Consultation for treatment of persons exposed to radiation may be obtained from REAC/TS at (615) 576– 3131 (day) or (615) 481–1000 (24-hour hotline) or from other sources listed on page 29. Ideally, decontamination should be performed immediately at the site of the accident. Attending personnel must be properly protected to prevent secondary contamination. After emergency care for life-threatening trauma has been administered, the patients’ contaminated clothing should be removed and double-bagged. The patients’ skin and hair should be flushed with water, and the contaminated water should be caught in a child’s play pool or other device for later disposal. A mild soap may be used to remove oily or adherent material. Monitoring the clean, dried skin with a beta-gamma counter between flushings will indicate the effectiveness of the decontamination procedure. If the accident occurs in inclement weather or at a site where washing facilities are unavailable or if the patient is in need of immediate medical care, decontamination may have to be delayed. In that case, care must be taken to prevent the spread of contamination during transport by wrapping the patient in blankets. If the hospital or other medical facility is not prepared to handle a patient who is externally contaminated with radioactivity, a temporary decontamination station can be set up at the medical care facility. It should be located outside, but if that is not feasible, it should be far removed from normal activity and other patient care areas. If decontamination is performed indoors, ventilation should be suspended so that no radioactivity escapes the room. Butcher paper taped to the floor and other surfaces is an effective barrier. All potentially contaminated material, including debrided tissue, must be collected in plastic bags for proper disposal. Attending personnel must be properly attired with disposable jumpsuits, gloves, or other protective equipment to avoid contamination through contact. The potential health consequences will depend on the boy’s interaction with the radioactive material. For example, it is not known whether the boy contacted the material and subsequently ingested radioactive material through hand-to-mouth activity, which would result in an internal contamination hazard. An external radiation hazard could exist if the boy contacted the material and is carrying radionuclides on his skin. Finally, the boy may have only approached the source, but may have been close enough to be exposed to beta and gamma radiation. Assuming no contact occurred and the boy’s proximity to the source were known, a radioactivity counter could provide dosimetric information that would aid in estimating his exposure. Maximum potential dose can also be calculated based on the characteristics of the source and the presumed location of the boy. The intensity of radiation decreases as the distance from the source increases, in accordance with the “inverse square” rule. It is unlikely that the occupants of the houseboat would be affected by beta radiation, which has a relatively short range and can usually be stopped by a few feet of air. Gamma radiation has greater penetration than beta radiation; therefore, gamma radiation could have reached the houseboat about 20 yards from the source. However, shielding by the houseboat or other structures could reduce the radiation. A gamma counter might be used to obtain direct dosimetric information inside the houseboat. In this case, it is unlikely that any steps will be required to protect the members of the community who rely on the river for drinking water; however, a public health official will make that determination. Iodide-131 has a radiation half-life of 8 days. In just 32 days (4 half-lives) the amount of radioactivity will be one-sixteenth of what it was originally. Dilution by the river will also reduce the concentration of radioactivity.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education Should the radioactivity level be of concern, an alternate source of water can be supplied to the community during the time required for the radioactive material to decay to a level that is considered to be safe by a health physicist. The antidote for radioactive iodide is early administration (within about 2 hours of ingestion of radioactive iodine) of SSKI (supersaturated potassium iodide [KI] solution) or iodide tablets. Stable iodide blocks absorption of iodide-131 in the thyroid. Oral administration of stable iodide is an effective and relatively inexpensive means to protect exposed residents of a community. Cesium-137 has a 30-year radiologic half-life. It would take 120 years for the radioactivity from this source to decay to one-sixteenth of its original value. The water could remain unusable for a prolonged period depending on the concentration of cesium-137 and the characteristics of the river (e.g., volume and flow rate). Cesium is distributed uniformly throughout the body and is rapidly eliminated by the kidneys. The experimental antidote for cesium is oral administration of ferric cyanoferrate (II). Commonly referred to as Prussian blue, this antidote binds the cesium ions that are enterically cycled and prevents their reabsorption from the gastrointestinal tract. The effectiveness of the antidote depends on the length of treatment and how soon after exposure it is started. However, Prussian blue is not approved by the Food and Drug Administration for general use or as an antidote for radioactive cesium. A radiation specialist at REAC/TS should be consulted before the antidote is administered. Challenge The RWF for beta or gamma radiation is one; therefore, a dose of 50 mrads of beta or gamma radiation is equivalent to 50 mrem or 0.05 rem. One Sievert equals 100 rem; therefore, 0.05 rem equals 0.0005 (5×10-4) Sv. The RWF for X radiation is also one; therefore, a dose of so mrads of X radiation would produce the same biologic effect as 50 mrads of gamma or beta radiation. Iodide-131 is not an alpha-emitter; however, if the radioactive material was emitting alpha particles and the material was ingested, the biologic effectiveness would be greater. The RWF for alpha particles is 20, which indicates a given dose of alpha radiation is twenty times more biologically effective than the same dose of beta or gamma radiation. Potential sources of radiation for the truck driver, as well as the general public, are as follows: Cosmic radiation and terrestrial radiation each produce an average dose rate of 30 mrem/year. Radon exposure provides an additional dose of about 200 mrem/year. Potassium-40 naturally present in human tissue contributes an average dose rate of about 65 mrem/year. Building and construction materials contribute variable dose rates. Occupants of wood frame buildings typically receive less than 10 mrem/year; occupants of masonry structures receive about 13 mrem/year. Atmospheric fallout provides an exposure dose rate of about 5 mrem/year. Consumer products, including tobacco, contribute a dose rate of less than 5 mrem/year when expressed as whole-body exposure. Medical diagnostic and therapeutic radiation is variable and generally applied locally; the average dose rate due to medical procedures is estimated to be 100 mrem/year. It is not likely that the radioactivity is the direct cause of the chest pain. If the iodide-131 vaporized and was inhaled, it would be absorbed from the lungs into the bloodstream and concentrated in the thyroid. However, this action would cause the patient no immediate discomfort. The cause of the chest pain must be sought elsewhere.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education If the boy had no physical contact with the radioactive material and was only irradiated by the gamma and beta energy, he is not a radiation hazard to others. Had the boy contacted the waste and radioactive material was transferred to his skin or clothing, then he would be a hazard because the residue would continue to emit radiation and irradiate those nearby, or he could secondarily contaminate others through contact. All three of these persons are at increased risk of cancer, and the risk increases in proportion to the dose of radiation received. If the boy did not contact the radioactive material, he presumably received less radiation than the driver and his assistant, and therefore, would be at much less risk. A small proportion of persons exposed to radiation will develop cancer as a result; if exposed persons do develop cancer, it may never be certain whether the cancer was the result of radiation exposure or other causes. (A carcinoma induced by radiation is histologically indistinguishable from other carcinomas). Acute radiation syndrome is characterized by nausea and vomiting, which begins within 1 to 4 hours after exposure and may last as long as 48 hours, with the extent of symptoms related to the severity of exposure. The onset of vomiting for these patients is delayed, occurring about 36 hours after exposure; therefore, it is unlikely that these symptoms are directly due to radiation exposure. The cause must be sought elsewhere (e.g., anxiety). If the onset of nausea and vomiting was as late as 4 hours after exposure, the hematopoietic subsyndrome would likely ensue, and illness due to bleeding and infection could develop. In either case, with appropriate supportive care, the driver and his assistant should recover. Pertinent clinical history includes proximity to the source and duration of the exposure. Whether gastrointestinal symptoms (nausea, vomiting, and diarrhea) have occurred is important because the time of onset of these symptoms can be inversely correlated with the severity of exposure. A complete blood count, including a lymphocyte count, can also help to estimate the severity of exposure; these tests should be repeated several times during the first few days after exposure. A useful and sensitive biomarker for radiation exposure in general is the chromosome aberration assay. Radiation induces several characteristic but nonspecific chromosomal abnormalities, particularly dicentric chromosomes, in peripheral blood lymphocytes. The optimum time to perform the assay is within hours to a few weeks after exposure. Only a few laboratories are prepared to perform and interpret this radiation cytogenetic assay; call REAC/TS at (615)–576–3131 (day) or (615) 481–1000 (24-hour hotline) for further information. Assuming the truck driver and his assistant experienced no internal contamination, treatment is supportive and symptomatic. See page 24 for a treatment scheme that is based on the degree of irradiation. During the next week, the boy’s lymphocyte count should be periodically checked; no other immediate follow-up is required. An ongoing medical surveillance program is unwarranted unless the clinical evidence contradicts the health physicist’s original estimate of maximum radiation exposure indicated in Challenge question 1. A whole-body dose of 50 mrads is similar to doses received in some medical diagnostic procedures. Fear is a natural reaction when people feel they may have been exposed to radiation. Reassurance is needed to alleviate the emotional and psychologic stresses that are caused when an accident involving radioactivity occurs. (See Ricks et al., 1991, in Suggested Reading List, page 29, for a discussion of the psychologic aspects of radiation exposure.) You could point out that the levels of radioactivity initially found in the river soon after the accident were low (i.e., 20 pCi/L). Depending on the dynamics of the river, the radioactivity level is likely to be even lower now. The proposed drinking water standard for iodine-131 is 108 pCi/L.

OCR for page 639
Environmental Medicine: Integrating a Missing Element into Medical Education To further reassure these patients, you could suggest that they have their water tested for radioactivity. You or the health physicist could also calculate the potential maximum amount of radiation exposure and compare this to information in the literature (e.g., Table 6, page 17). No immediate clinical symptoms have been associated with the amount of radiation these patients were likely to have received by ingesting or contacting the contaminated water, and the additional long-term risk of cancer at these radiation levels is negligible.