Radiation Injuries

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Definition

Radiation injuries is damage caused by ionizing radiation emitted by the sun, x-ray machines, and radioactive elements.

Description

Radio and television signals, radar, heat, infrared, ultraviolet, sunlight, starlight, cosmic rays, gamma rays, and x rays all belong to the electromagnetic spectrum and differ only in their relative energy, frequency, and wavelength. These waves all travel at the speed of light, and unlike sound they can all travel through empty space. The frequencies above visible light have enough energy to penetrate and cause damage to living tissue, damage that can be as minor as a sunburn caused by ultraviolet light or as extreme as the incineration of Hiroshima, Japan, during World War II. Lower frequencies do not penetrate, but can cause eye and skin damage, primarily due to the heat they transmit.

Atomic particles can also have enough energy to do damage. They come from radioactive isotopes as they decay to stable elements. Electrons are called beta particles when they radiate. Alpha particles are the nuclei of helium atoms—two protons and two neutrons—without the surrounding electrons. Alpha particles are too large to penetrate a piece of paper unless they are greatly accelerated in electric and magnetic fields. Other subatomic particles are much less common outside of nuclear reactors and particle accelerators.

The energy of electromagnetic radiation is a direct function of its frequency. The high-energy, high-frequency waves, which can penetrate solids to various depths, cause damage by separating molecules into electrically charged pieces, a process known as ionization. Atomic particles, cosmic rays, gamma rays, x rays, and some ultraviolet are called ionizing radiation. The pieces they generate are called free radicals. They act like acid, but they last only fractions of a second before they revert to harmless forms. Adjusting the energy of therapeutic radiation can select a depth at which it will do the most damage. Ionizing radiation also does damage to chromosomes by breaking strands of DNA. DNA is so good at repairing itself that both strands of the double helix must be broken to produce genetic damage.

Because radiation is energy, it can be measured. There are a number of units used to quantify radiation energy. Some refer to effects on air, others to effects on living tissue. The roentgen, named after Wilhelm Conrad Roentgen, who discovered x rays in 1895, measures ionizing energy in air. A rad expresses the energy transferred to tissue. The rem measures tissue response. A roentgen generates about a rad of effect and produces about a rem of response. The gray and the sievert are international units equivalent to 100 rads and rems, respectively. A curie, named after French physicists who experimented with radiation, is a measure of actual radioactivity given off by a radioactive element, not a measure of its effect. The average annual human exposure to natural background radiation is roughly 3 milliSieverts (mSv).

It is reasonable to presume that any amount of ionizing radiation will produce some damage. However, there

is radiation everywhere, from the sun (cosmic rays) and from traces of radioactive elements in the air (radon) and the ground (uranium, radium, carbon-14, potassium-40 and many others). Earth's atmosphere protects us from most of the sun's radiation. Living at 5,000 feet altitude in Denver, Colorado, doubles exposure to radiation, and flight in a commercial airliner increases it 150-fold by lifting us above 80% of that atmosphere. Because no amount of radiation is perfectly safe and because radiation is ever present, arbitrary limits have been established to provide some measure of safety for those exposed to unusual amounts. Less than 1% of them reach the current annual permissible maximum of 50 mSv.

One of the most remarkable bits of information to come out of studies of Japanese people exposed to atomic bomb irradiation in 1945 is the absence of genetic damage to survivors. Forty years of studying 76,000 children has detected no increase in abnormal pregnancies or chromosomes. This evidence suggests that it takes about 1 Sv of gonad radiation to double human mutations caused by background radiation, and that background radiation causes less than 1% of these mutations. Other organisms are much more susceptible than humans to mutations from radiation.

Ionizing radiation has many uses in medicine, both in diagnosis and in treatment. X rays and CT scanners use it to form images of the body's insides. Nuclear medicine uses radioactive isotopes to diagnose and to treat medical conditions. In the body, radioactive elements localize to specific tissues and give off tiny amounts of radiation. Detecting that radiation provides information on both anatomy and function. Radioactive chemicals are also used to treat certain conditions, most commonly an overactive thyroid. Because the thyroid is the only gland in the body to utilize iodine, all iodine in the body is concentrated there. A radioactive isotope of iodine (I-131) will gradually destroy overactive thyroid tissue, curing the disease. The dosage must be carefully measured and even then sometimes does too good a job. Since it is easier to replace inadequate thyroid than to deal with too much, this treatment is very acceptable.

Early workers with x rays frequently died from its long term effects, notably leukemia. Wrist watches used to glow in the dark due to radium that was painted on the dial and watch hands. This work was done by workers who moistened their brushes with their tongues. Many of them developed cancer of the tongue. After lessons like these, most sources of man-made radioactivity have been eliminated from the environment. Watches no longer glow in the dark from radium. Shoe salesmen no longer use fluoroscopes to check shoes for a proper fit. Today, doses used for medical examinations are ordinarily too small to be of concern. Methods of magnification, lead shielding, and a greater awareness of the risks have all but eliminated the danger from diagnostic radiation. It adds on average only 0.6 Sv a year, or 20% of the background radiation. Nevertheless, people who work around x rays monitor their exposure, because there is no such thing as a completely safe dose.

It is therapeutic, accidental, and deliberate radiation that does the obvious damage. There has not been much in the way of deliberate radiation damage since Nagasaki, but accidental radiation exposure happens periodically. Between 1945 and 1987, there were 285 nuclear reactor accidents, injuring over 1,550 people and killing 64. The most striking example, and the only one to endanger the public, was the meltdown of the graphite core nuclear reactor at Chernobyl in 1986, which spread a cloud of radioactive particles across the entire continent of Europe. Information about radiation effects is still being gathered from that disaster. There have also been a few accidents with medical and industrial radioactivity.

Nevertheless, it is believed that radiation is responsible for less than 1% of all human disease and for about 3% of all cancers. This figure does not include lung cancer from environmental radon, because that information is unknown. The figure could be significant, but it is greatly confounded by the similar effects of tobacco.

Because cancers are usually faster growing than their host tissues, they can be selectively killed by carefully measured radiation. This is most true of the lymphomas. Other cancers are less radiosensitive. Whenever radiation is used to treat cancer, care must be taken to measure the dose carefully and aim it as accurately as possibly. Even so, many cancers differ so little from the surrounding tissue in their sensitivity that undesirable damage is unavoidable. Skin will become thin making the blood vessels very visible. Bowels will become irritated and cause vomiting and diarrhea. Other organs may scar and decrease their function. Bone marrow is always at risk of damage. Fortunately, the bone marrow is so widely spread throughout the body that localized treatment damages only a part of it. A typical therapeutic dose of radiation to a localized area is about 2 Gy (grays) per day, repeated at intervals to a total dose that varies with the type of cancer being treated.

Newer techniques of directing radiation are providing greater safety for equivalent tumor doses of radiation. One method uses several different beams of radiation so that only the point of their convergence receives the full dose. A gamma knife is a new surgical tool that focuses radiation with extreme accuracy in three dimensions, sparing closely surrounding tissue from the radiation effects. It focuses 201 Cobalt-60 or linear accelerator sources without need for a surgical incision.

— J. Ricker Polsdorfer, MD

Definition

Radiation injuries are caused by ionizing radiation emitted by such sources as the sun, x-ray and other diagnostic machines, tanning beds, and radioactive elements

released in nuclear power plant accidents and detonation of nuclear weapons during war and as terrorist acts.

Description

Ionizing radiation is made up of unstable atoms that contain an excess amount of energy. In an attempt to stabilize, the atoms emit the excess energy into the atmosphere, creating radiation. Radiation can either be electromagnetic or particulate.

The energy of electromagnetic radiation is a direct function of its frequency. The high energy, high frequency waves that can penetrate solids to various depths cause damage by separating molecules into electrically charged pieces, a process known as ionization. X rays are a type of electromagnetic radiation. Atomic particles come from radioactive isotopes as they decay to stable elements. Electrons are called beta particles when they radiate. Alpha particles are the nuclei of helium atoms—two protons and two neutrons—without the surrounding electrons. Alpha particles are too large to penetrate a piece of paper unless they are greatly accelerated in electric and magnetic fields. Both beta and alpha particles are types of particulate radiation. When over-exposure to ionizing radiation occurs, there is chromosomal damage in deoxyribonucleic acid (DNA). DNA is very good at repairing itself; both strands of the double helix must be broken to produce genetic damage.

Because radiation is energy, it can be measured. There are a number of units used to quantify radiation energy. Some refer to effects on air, others to effects on living tissue. The roentgen, named after Wilhelm Conrad Roentgen, who discovered x rays in 1895, measures ionizing energy in air. A rad expresses the energy transferred to tissue. The rem measures tissue response. A roentgen generates about a rad of effect and produces about a rem of response. The gray and the sievert are international units equivalent to 100 rads and rems, respectively. A curie, named after French physicists who experimented with radiation, is a measure of actual radioactivity given off by a radioactive element, not a measure of its effect. The average annual human exposure to natural background radiation is roughly 3 milliSieverts (mSv).

Any amount of ionizing radiation will produce some damage; however, there is radiation everywhere, from the sun (cosmic rays) and from traces of radioactive elements in the air (radon) and the ground (uranium, radium, carbon-14, potassium-40 and many others). Earth's atmosphere protects us from most of the sun's radiation. Living at 5,000 feet altitude in Denver, Colorado, doubles exposure to radiation, and flight in a commercial airliner increases it 150-fold by lifting us above 80% of that atmosphere. Because no amount of radiation is perfectly safe and because radiation is ever present, arbitrary limits have been established to provide some measure of safety for those exposed to unusual amounts. Less than 1% of them reach the current annual permissible maximum of 20 mSv.

A 2001 ruling by the Federal Court of Australia indicated that two soldiers died from cancer caused by minimal exposure to radiation while occupying Hiroshima in 1945. The soldiers were exposed to less than 5 mSv of radiation. The international recommendation for workers is safety level of up to 20 mSv. The ruling and its support by many international agencies suggests that even extremely low doses of radiation can be potentially harmful.

Ultraviolet (UV) Radiation Exposure from the Sun and Tanning Beds

UV radiation from the sun and tanning beds and lamps can cause skin damage, premature aging, and skin cancers. Malignant melanoma is the most dangerous of skin cancers and there is a definite link between type UVA exposure used in tanning beds and its occurrence. UVB type UV radiation is associated with sunburn, and while not as penetrating as UVA, it still damages the skin with over exposure. Skin damage accumulates over time, and effects do not often manifest until individuals reach middle age. Light-skinned people who most often burn rather than tan are at a greater risk of skin damage than darkerskinned individuals that almost never burn. The U.S. Food and Drug Administration (FDA) and the Centers for Disease Control (CDC) discourage the use of tanning beds and sun lamps and encourage the use of sunscreen with at least an SPF of 15 or greater. In addition, the rising incidence of melanoma in the United States has led the Environmental Protection Agency (EPA) to develop a sun safety education program for school-age children in order to begin changing public attitudes toward tanning.

Overexposure During Medical Procedures

Ionizing radiation has many uses in medicine, both in diagnosis and in treatment. X rays, CT scanners, and fluoroscopes use it to form images of the body's insides. Nuclear medicine uses radioactive isotopes to diagnose and to treat medical conditions. In the body, radioactive elements localize to specific tissues and give off tiny amounts of radiation. Detecting that radiation provides information on both anatomy and function. During the past 10 years, skin injuries caused by too much exposure during a medical procedure have been documented. In 1995, the FDA issued a recommendation to physicians and medical institutions to record and monitor the dosage of radiation used during medical procedures on patients in order to minimize the amount of skin injuries. The FDA suggested doses of radiation not exceed 1 Grey (Gy). (A Grey is roughly equivalent to a sievert.) As of 2001, the FDA was preparing further guidelines for fluoroscopy, the procedure most often associated with medical-related radiation skin injuries such as rashes and more serious burns and tissue death. Injuries occurred most often during angioplasty procedures using fluoroscopy.

CT scans of children have also been problematic. Oftentimes the dosage of radiation used for an adult isn't decreased for a child, leading to radiation overexposure. Children are more sensitive to radiation; a February 2001 study indicates 1,500 out of 1.6 million children under 15 years of age receiving CT scans annually will develop cancer. Studies show that decreasing the radiation by half for CT scans of children will effectively decrease the possibility of overexposure while still providing an effective diagnostic image. The benefits to receiving the medical treatment utilizing radiation is still greater than the risks involved; however, more stringent control over the amount of radiation used during the procedures will go far to minimize the risk of radiation injury to the patient.

Recent evidence suggests that some ethnic groups may be more vulnerable than others to radiation damage. A study done at New York University found that Jews are more likely to develop ovarian cancer as a delayed side effect of diagnostic x-rays of the abdomen than non-Jews. These findings require confirmation by further research, but they do indicate that ethnicity and other genetic factors are involved in susceptibility to radiation damage.

Side Effects from Radiation Therapy to Treat Cancer

As many as half of all cancer patients receive some form of radiation therapy as a component of treatment.

The therapy can be delivered from either an external or an internal source, although the former is more common. The machines used for external radiation have become more specialized to deliver the appropriate dose to either a superficial or a deep location on the body. Depending on the type and site of cancer being treated, internal sources of radiation can be injected, swallowed, or placed within the body in sealed containers. These are implanted into or near the tumor, either temporarily or permanently.

Some types of tumors may be eliminated by radiation therapy, if the patient is able to withstand the necessary dose. In other cases, radiation is used in conjunction with other methods of treatment. It may be given before surgery, to shrink a tumor to an operable size, or after surgery, to try to destroy any cancerous cells that may remain. Radiation can be used to make patients with incurable disease more comfortable by decreasing the bulk of tumors to reduce pain or pressure. Treatment that is given as a comfort measure only is known as palliation, or palliative therapy.

Occupational Radiation Exposure

Specialists in industrial and occupational health are increasingly aware of the rising number of injuries related to on-the-job radiation exposure. One study of Swedish workers exposed to high levels of low-frequency magnetic fields found an increased incidence of kidney, liver, and pituitary gland tumors among the men, and a higher rate of leukemia and brain tumors among the women.

Sadly, the delayed effects of occupational radiation exposure have also delayed the adoption of necessary protection for workers at risk. A study of the high rate of lung cancer among Navajo Indians who worked in uranium mines during World War II did not bring about even partial protection for the miners until 1962. It was not until 1990 that Congress passed the Radiation Exposure Compensation Act to provide care for the injured miners. he effects of cosmic radiation on human beings are also being investigated because of concern for the safety of air crew. Although findings are still inconclusive as of 2002, recent reports of an increased incidence of cancer among airline pilots and cabin crew members have led epidemiologists to study the long-term effects of cosmic radiation at the altitudes of modern aircraft flight.

Radiation Exposure from Nuclear Accidents, Weaponry, and Terrorist Acts

Between 1945 and 1987, there were 285 nuclear reactor accidents, injuring over 1,550 people and killing 64. The most striking example was the meltdown of the graphite core nuclear reactor at Chernobyl in 1986, which spread a cloud of radioactive particles across the entire continent of Europe. Information about radiation effects is still being gathered from that disaster, however 31 people were killed in the immediate accident and 1,800 children have thus far been diagnosed with thyroid cancer. In a study published in May 2001 by the British Royal Society, children born to individuals involved in the cleanup of Chernobyl and born after the accident are 600% more likely to have genetic mutations than children born before the accident. These findings indicate that exposure to low doses of radiation can cause inheritable effects.

Since the terrorist attack on the World Trade Center and the Pentagon on September 11, 2001, the possibility of terrorist-caused nuclear accidents has been a growing concern. All 103 active nuclear power plants in the United States are on full alert, but they are still vulnerable to sabotage such as bombing or attack from the air. A nofly zone of 12 miles below 18,000 feet has been established around nuclear power plants by the Federal Aviation Administration (FAA). There is also growing concern over the security of spent nuclear fuel—more than 40,000 tons of spent fuel is housed in buildings at closed plants around the country. Unlike the active nuclear reactors that are enclosed in concrete-reinforced buildings, the spent fuel is stored in non-reinforced buildings. Housed in cooling pools, the spent fuel could emit dangerous levels of radioactive material if exploded or used in makeshift weaponry. Radioactive medical and industrial waste could also be used to make "dirty bombs." Since 1993, the Nuclear Regulatory Commission (NRC) has reported 376 cases of stolen radioactive materials.

One response on the part of health care workers has been stepped-up training in radiation disaster management. Emergency department personnel are being trained as of 2002 to use radiologic monitoring and other specialized equipment for treating victims of a terrorist attack involving radiation.

Causes & Symptoms

Radiation can damage every tissue in the body. The particular manifestation will depend upon the amount of radiation, the time over which it is absorbed, and the susceptibility of the tissue. The fastest growing tissues are the most vulnerable, because radiation as much as triples its effects during the growth phase. Bone marrow cells that make blood are the fastest growing cells in the body. A fetus in the womb is equally sensitive. The germinal cells in the testes and ovaries are only slightly less sensitive. Both can be rendered useless with very small doses of radiation. More resistant are the lining cells of the body—skin and intestines. Most resistant are the brain cells, because they grow the slowest.

The length of exposure makes a big difference in what happens. Over time the accumulating damage, if not enough to kill cells outright, distorts their growth and causes scarring and/or cancers. In addition to leukemias, cancers of the thyroid, brain, bone, breast, skin, stomach, and lung all arise after radiation. Damage depends, too, on the ability of the tissue to repair itself. Some tissues and some types of damage produce much greater consequences than others.

There are three types of radiation injuries.

• External irradiation: as with x-ray exposure, all or part of the body is exposed to radiation that either is absorbed or passes through the body.
• Contamination: as with a nuclear accident, the environment and its inhabitants are exposed to radiation. People are affected internally, externally, or with both internal and external exposure.
• Incorporation: dependent on contamination, the bodies of individuals affected incorporate the radiation chemicals within cells, organs, and tissues and the radiation is dispersed throughout the body.

Immediately after sudden irradiation, the fate of those affected depends mostly on the total dose absorbed. This information comes mostly from survivors of the atomic bomb blasts over Japan in 1945.

• Massive doses incinerate immediately and are not distinguishable from the heat of the source.
• A sudden whole-body dose over 50 Sv produces such profound neurological, heart, and circulatory damage that patients die within the first two days.
• Doses in the 10–20 Sv range affect the intestines, stripping their lining and leading to death within three months from vomiting, diarrhea, starvation, and infection.
• Victims receiving 6–10 Sv all at once usually escape an intestinal death, facing instead bone marrow failure and death within two months from loss of blood coagulation factors and the protection against infection provided by white blood cells.
• Between 2–6 Sv gives the person a fighting chance for survival if he or she is supported with blood transfusions and antibiotics.
• One or two Sv produces a brief nonlethal sickness with vomiting, loss of appetite, and generalized discomfort.

Side Effects of Radiation Therapy

Damage caused to normal cells can show up either in the time frame shortly following radiation treatment, or as long as years after radiation has been completed. Symptoms that frequently occur soon after treatment include loss of appetite, fatigue, and skin changes. Less commonly, patients have headache, nausea, vomiting, hair loss, and weakness. In more severe cases, dehydration, seizures, and shock-type reactions can occur. The severity and type of effects will depend on the region of the body receiving treatment, the type of radiation used during the course of treatment, and the dose. There is also individual variation in the response. Skin rashes are common. They may take the form of redness, burn, dryness, itching, or soreness. Organs that were in the path of the beam may show changes, including scarring, functional changes (such as decrease in elasticity), and loss of cells. Tissues that have a rapid turnover of cells may be most severely affected, including the skin and lining of the gastrointestinal tract. More severe injuries may include long-term bone marrow suppression, and occasionally even other cancers, particularly sarcomas.

People who receive radiation in the region of the head and neck are likely to experience a dry and sore mouth to some degree. The skin may become dry, and the area under the chin may droop. Sense of taste can be altered or lost. Some may experience hair loss, earaches, or difficulty swallowing due to inflammation of the esophagus.

Radiation treatments given for or around the breast, chest, or lung can also cause esophagitis and accompanying trouble swallowing. Changes in the lung tissue may lead to pneumonitis or pulmonary fibrosis. The patient may develop a cough. Breast treatments may cause pain and swelling. Blood counts can decrease.

Side effects from treatment of the stomach and abdominal area can induce nausea and diarrhea. In the pelvic region, radiation may result in difficulties with urination, and infertility in both males and females. Women may also have symptoms of dryness, itching, or burning of the vagina.

Diagnosis

The various effects of radiation on the body are well recognized. Patients who are scheduled to undergo radioactive treatments should be informed of the potential side effects they will encounter based on the area being treated and the dose of radiation being used. Advice for coping with minor injuries should be given, as well as descriptions of what symptoms should prompt a call or a visit to the treating physician.

Treatment

It is clearly important to have some idea of the dose received as early as possible, so that attention can be directed to those victims in the 2-10 Sv range that might survive with treatment. Blood transfusions, protection from infection in damaged organs, and possibly the use of newer stimulants to blood formation can save many victims in this category.

Local radiation exposures usually damage the skin and require careful wound care, removal of dead tissue, and skin grafting if the area is large. Again infection control is imperative.

One of the best-known, and perhaps even mainstream, treatments of radiation injury is the use of Aloe vera preparations on damaged areas of skin. It has demonstrated remarkable healing properties even for chronic ulcerations resulting from radiation treatment. Another topical herb that may be effective against skin inflammation following radiation therapy is chamomile cream. Studies support the benefits of chamomile for skin inflammation and wound healing. Additional topical herbs that may be helpful are calendula and St. John's wort. These therapies can prove very helpful since skin reaction is one of the most common side effects of radiation therapy.

Guided imagery is a method that may be used following radiation treatment, especially to help ease pain. Several nutritional supplements help with healing wounds. These include essential fatty acids (Omega 3 and 6), vitamin A, vitamin B, and magnesium/zinc.

If the tumor being treated is determined to be sensitive to radiation, there are a few herbs that are said to reduce the adverse effects of radiation exposure. Ginseng is one that research suggests may have this benefit. Other nutrients thought to have some protective effects are coenzyme Q10, kelp, pantothenic acid, and glutathione with L-cysteine and L-methionine. Garlic and vitamin C support immune function. Grape seed extract is a powerful antioxidant that protects against cell damage by free radicals. Any nutritional measures to support optimum health before treatment are beneficial.

Allopathic Treatment

The type of treatment used depends on the area and severity of the injury. Something as serious as bone marrow suppression would require more intensive therapy, whereas more minor conditions are treated symptomatically. Radiation-induced esophagitis may necessitate intravenous or gastrostomy feeding for a time until the injury is healed. If a perforation or a stricture develops, surgery may be necessary. Products are available to keep the eyes (drops with vitamin A) and oral mucosa moist, as the cells producing mucus and tears are often damaged.

Expected Results

Tissue damage resulting from radiation exposure tends to be chronic in nature, and may even be progressive. For the lesser and more common types of problems, long-term treatment of symptoms should be anticipated.

Prevention

Part of preventing radiation injury involves doing research on the condition being treated. It is a good idea to be certain that radiation is the best available treatment for a particular cancer type before embarking on a course of therapy.

Information on preventing or minimizing damage from radiation produced by terrorist devices or other nuclear emergencies is available in a series of fact sheets that can be downloaded from the Centers for Disease Control (CDC) web site. The fact sheets cover such topics as basic radiation facts, acute radiation sickness (ARS), dirty bombs, effects of radiation on health, possible effects of radiation on unborn children, and protective measures in the case of a nuclear event.

Resources

Books

Altman, Robert, and Michael Sarg. The Cancer Dictionary, revised edition. New York: Checkmark Books, 2000.

Balch, James, and Phyllis Balch. Prescription for Nutritional Healing. New York: Avery Publishing Group, 1997.

Johns Hopkins University. Johns Hopkins Family Health Book. New York: HarperCollins Publishers, 1999.

Periodicals

Brugge, D., and R. Goble. "The History of Uranium Mining and the Navajo People." American Journal of Public Health 92 (September 2002): 1410-1419.

"'Dirty Bomb' Threat Puts Spotlight on Unprepared EDs: Do You Have a Plan?" ED Management 14 (September 2002): 97-100.

Fears, T. R., C. C. Bird, D. Guerry 4th, et al. "Average Midrange Ultraviolet Radiation Flux and Time Outdoors Predict Melanoma Risk." Cancer Research 62 (July 15, 2002): 3992-3996.

Grunwald, Michael and Peter Behr. "Are Nuclear Plants Secure? Industry Called Unprepared for Sept. 11-Style Attack." Washington Post, November 3, 2001, p. A01.

Hakansson, N., B. Floderus, P. Gustavsson, et al. "Cancer Incidence and Magnetic Field Exposure in Industries Using Resistance Welding in Sweden." Occupational and Environmental Medicine 59 (July 2002): 481-486.

Harlap, S., S. H. Olson, R. R. Barakat, et al. "Diagnostic X Rays and Risk of Epithelial Ovarian Carcinoma in Jews." Annals of Epidemiology 12 (August 2002): 426-434.

Lim, M. K. "Cosmic Rays: Are Air Crew at Risk?" Occupational and Environmental Medicine 59 (July 2002): 428-432.

Vergano, Dan. "'Dirty' Bombs Latest Fear." USA Today, November 3, 2001.

Organizations

American College of Occupational and Environmental Medicine (ACOEM). 1114 North Arlington Heights Road, Arlington Heights, IL 60004. (847) 818-1800. .

Centers for Disease Control and Prevention (CDC). 1600 Clifton Road, Atlanta, GA 30333. (404) 639-3311. .

[Article by: Judith Turner; Rebecca J. Frey, PhD]

For more information on radiation injury, visit Britannica.com.