Radiation injury is damage to tissues caused by exposure to ionizing radiation.
In general, ionizing radiation refers to high-energy electromagnetic waves (x-rays and gamma rays) and particles (alpha particles, beta particles, and neutrons) that are capable of stripping electrons from atoms (ionization). Ionization changes the chemistry of affected atoms and any molecules containing those atoms. By changing molecules in the highly ordered environment of the cell, ionizing radiation can disrupt and damage cells. Cellular damage can cause illness, increase the risk of developing cancer, or both.
Ionizing radiation is emitted by radioactive substances (radionuclides), such as uranium, radon, and plutonium. It is also produced by man-made devices, such as x-ray and radiation therapy machines.
Radio waves, such as from cell phones and AM and FM transmitters, and visible light also are forms of electromagnetic radiation. However, because of their lower energy, these forms of radiation are not ionizing, and thus public exposure levels from these common sources do not damage cells. In this discussion, “radiation” refers exclusively to ionizing radiation.
Measurement of Radiation:
The amount of radiation is measured in several different units. The roentgen (R) is a measure of the ionizing ability of radiation in air and is commonly used to express the intensity of exposure to radiation. How much radiation people are exposed to and how much is deposited in their body may be very different. The gray (Gy) and sievert (Sv) are measures of the dose of radiation, which is the amount of radiation deposited in matter, and are the units used to measure dose in humans after exposure to radiation. The Gy and Sv are similar, except the Sv takes into account the effectiveness of different types of radiation to cause damage and the sensitivity of different tissues in the body to radiation. Low levels of exposure are measured in mGy (1 mGy = 1/1000 Gy) and mSv (1 mSv = 1/1000 Sv).
Contamination vs. Irradiation:
The two main types of radiation exposure are contamination and irradiation. Many of the most significant radiation accidents have exposed people to both.
Contamination is contact with and retention of radioactive material, usually as a dust or liquid. External contamination is that on skin or clothing, from which some can fall or be rubbed off, contaminating other people and objects. Internal contamination is radioactive material deposited within the body, which it may enter by ingestion, inhalation, or through breaks in the skin. Once in the body, radioactive material may be transported to various sites, such as the bone marrow, where it continues to emit radiation, increasing the dose, until it is removed or emits all its energy (decays). Internal contamination is more difficult to remove than external contamination.
Irradiation is exposure to radiation but not to radioactive material, that is, no contamination is involved. A common example is diagnostic x-rays, such as for a broken bone. Radiation exposure can occur without direct contact between people and the source of radiation (such as radioactive material or an x-ray machine). When the source of the radiation is removed or turned off, irradiation ends. People who are irradiated but not contaminated are not radioactive, that is, they do not emit radiation, and their dose from that source of radiation does not continue to increase.
Sources of Radiation Exposure
People are exposed constantly to low levels of radiation, naturally occurring (background radiation), and intermittently to radiation from man-made sources. In the United States, people receive on average about 3 mSv per year from natural sources and 3 mSv per year from man-made sources, for a total of 6 mSv per year. However, in some parts of India, Iran, Brazil, and China, the average radiation dose from background is higher, between 5 and 10 mSv per year.
Sources of background radiation include cosmic radiation from outer space and naturally occurring radioactive elements.
Cosmic radiation is significantly blocked by the earth's atmosphere but is concentrated at the north and south poles by the earth's magnetic field. Thus, exposure to cosmic radiation is greater for people living closer to the poles, living at high altitudes, and during airplane flights.
Radioactive elements, particularly uranium and the radioactive products into which it naturally decays (such as radon gas), are present in many rocks and minerals. These elements end up in various substances, including food, water, and construction materials. Radon exposure typically accounts for about two thirds of peoples' exposure to naturally occurring radiation. The doses from natural background radiation are far too low to cause radiation injury.
Most people's exposure to man-made sources of radiation involves medical imaging tests (particularly computed tomography [CT] and cardiac nuclear medicine scans). Medical diagnostic tests such as chest x-rays, mammograms, and dental x-rays do not deliver doses sufficient to cause radiation injury. People who are receiving radiation treatments for cancer may receive very high doses of radiation. However, every effort is made to deliver the radiation only to diseased tissues and to minimize the radiation to normal tissues.
Exposure also occurs from other sources, such as radiation accidents and fallout from nuclear weapons testing. However, these exposures represent a minor part of most people's annual exposure. Typically, radiation accidents involve people who work with radioactive materials and with x-ray sources, such as food irradiators and industrial x-ray machines. Such people may receive significant doses of radiation. These injuries commonly result from failure to follow safety procedures. Radiation exposure has also occurred from lost or stolen medical or industrial sources containing large amounts of radioactive material.
Rarely, radioactive material has been released from nuclear power plants, including the Three Mile Island plant in Pennsylvania in 1979 and the Chernobyl plant in the Ukraine in 1986. The Three Mile Island accident did not result in major radiation exposure. In fact, people living within 1 mile (1.6 kilometers) of the plant received only about 0.08 mSv additional radiation. However, people living near the Chernobyl plant received an average dose of about 300 mSv. More than 30 workers and emergency responders died, and many more were injured. There was low-level contamination from Chernobyl as far away as Europe, Asia, and even the United States. The average cumulative radiation dose for the general population in contaminated areas (various regions of Belarus, Russia, and Ukraine) over a 20-year period after the accident was estimated to be between 10 and 30 mSv. It should be noted that the average annual extra dose (0.5 to 1.5 mSv per year) received by residents of the territories contaminated by Chernobyl fallout is generally lower than typical background radiation in the United States.
Nuclear weapons release massive amounts of energy and radiation. These weapons have not been used against people since 1945. However, several nations now have nuclear weapons, and terrorist groups have also tried to obtain them or build their own, increasing the possibility that these weapons will again be used. The vast majority of the casualties from the detonation of a nuclear weapon result from the blast and thermal burns. A smaller fraction of the casualties (although still a high number) result from radiation-induced illness.
The possibility of intentional radiation exposure through terrorist activities includes the use of a device to contaminate an area by dispersing radioactive material (a radiation dispersal device that uses conventional explosives is referred to as a dirty bomb). Other terrorist scenarios include using a hidden radiation source to expose unsuspecting people to large doses of radiation, attacking a nuclear reactor or radioactive material storage facility, and detonating a nuclear weapon.
Effects of Radiation
The damaging effects of radiation depend on several factors:
A single, rapid dose of radiation to the entire body can be fatal, but the same total dose given over a period of weeks or months may have much less effect. The effects of radiation also depend on how much of the body is exposed. For example, more than 6 Gy is usually fatal when the radiation is distributed over the entire body. However, when concentrated in certain small areas and spread out over a period of weeks or months, as in radiation therapy for cancer, 10 or more times this amount can be given without serious harm.
Some parts of the body are more sensitive to radiation. Organs and tissues in which cells multiply quickly, such as the intestine and bone marrow, are harmed more easily by radiation than those in which cells multiply more slowly, such as muscles and brain cells. The thyroid gland is susceptible to cancer after being exposed to radioactive iodine because radioactive iodine concentrates in the thyroid gland.
Radiation and Children:
Children are more susceptible to radiation injury because their cells typically divide more rapidly than those of adults.
The fetus is exceptionally sensitive to damage from radiation. In the fetus, exposure in excess of 300 mGy during 8 to 25 weeks after conception may cause reduced intelligence and poor school performance. Birth defects may occur due to exposure in the womb to high doses of radiation. However, at doses less than 100 mGy, particularly at the even lower doses used in imaging tests a pregnant woman might typically undergo, there is no apparent increase beyond the normal risk of having a birth defect.
Radiation and Cancer:
A large radiation exposure increases the risk of cancer because of damage to the genetic material (DNA) in cells that survive the radiation. However, radiation is a weaker cause of cancer than people think. Even a whole-body dose of 1 Gy (over 300 times more than the average annual background radiation dose) increases a typical person's lifetime risk of dying from cancer from 25% to about 30%.
Children's risk of radiation-induced cancer is several times higher than that of adults. Children may be more susceptible because their cells divide more often and because they have a longer lifespan during which cancer may develop. The lifetime risk of cancer for a 1-year-old who has a CT scan of the abdomen is estimated to increase by 0.18%.
Radiation and Inherited Defects:
In animals, irradiation of the ovaries or testes at high doses has been shown to lead to defective offspring (hereditary effects). However, no increase in the percentage of birth defects was observed in the children of survivors of the nuclear detonations in Japan. It may be that the radiation exposure was not high enough to cause a measurable increase.
Symptoms depend on whether radiation exposure involves the whole body or is limited to a small portion of the body. At high doses, whole-body exposure causes acute radiation illness, and partial-body exposure causes local radiation injury.
Acute Radiation Illness:
Acute radiation illness typically occurs in people whose entire body has been exposed to very high doses of radiation all at once or over a short period of time. Doctors divide acute radiation syndromes into three groups based on the main organ system affected, although there is overlap among these groups:
Acute radiation illness usually progresses through three stages:
Which syndrome develops, its severity, and its rate of progression depend on the radiation dose. As the dose increases, symptoms develop earlier, progress more rapidly (for example, from prodromal symptoms to the various organ system syndromes), and become more severe.
The severity and time course of the early symptoms are fairly consistent from person to person for a given amount of radiation exposure. Thus, doctors often can estimate a person's radiation exposure from the timing, nature, and severity of the early symptoms.
The hematopoietic syndrome is caused by the effects of radiation on the bone marrow, spleen, and lymph nodes—the primary sites of blood cell production (hematopoiesis). Loss of appetite (anorexia), lethargy, nausea, and vomiting may begin 1 to 6 hours after exposure to 1 to 6 Gy of radiation. These symptoms resolve within 24 to 48 hours after exposure, and people feel well for a week or more. During this symptom-free period, the blood-producing cells in the bone marrow, spleen, and lymph nodes begin to waste away and are not replaced, leading to a severe shortage of white blood cells, followed by a shortage of platelets and then red blood cells. The shortage of white blood cells can lead to severe infections. The shortage of platelets may cause uncontrolled bleeding. The shortage of red blood cells (anemia) causes fatigue, weakness, paleness, and difficulty breathing with physical exertion. After 4 to 5 weeks, if people survive, blood cells begin to be produced once more, but people feel weak and tired for months.
The gastrointestinal syndrome is due to the effects of radiation on the cells lining the digestive tract. Severe nausea, vomiting, and diarrhea may begin in less than 1 hour after exposure to 6 Gy or more of radiation. The symptoms may lead to severe dehydration, but they resolve within 2 days. During the next 4 or 5 days (latent stage), people feel well, but the cells lining the digestive tract, which normally act as a protective barrier, die and are shed. After this time, severe diarrhea—often bloody—returns, once more resulting in dehydration. Bacteria from the digestive tract may invade the body, producing severe infections. People who have received this much radiation also develop the hematopoietic syndrome, which results in bleeding and infection and increases their risk of death. After exposure to 6 Gy or more of radiation, death is common. However, with advanced medical support, about 50% of people may survive.
The cerebrovascular syndrome occurs when the total dose of radiation exceeds 20 to 30 Gy. People rapidly develop confusion, nausea, vomiting, bloody diarrhea, tremors, and shock. The latent phase is brief or absent. Within hours, blood pressure falls, accompanied by seizures and coma. The cerebrovascular syndrome is always fatal within a few hours to 1 or 2 days.
Local Radiation Injury:
Radiation therapy for cancer is one of the most common causes of local radiation injuries. Other causes produce similar symptoms. Symptoms depend on the amount of radiation and the area of the body treated.
Nausea, vomiting, and loss of appetite may occur during or shortly after irradiation of the brain or abdomen. Large amounts of radiation to a limited area of the body often damage the skin over that area. Skin changes include hair loss, redness, peeling, sores, and, possibly eventual thinning of the skin and dilated blood vessels just beneath the skin's surface (spider veins). Radiation to the mouth and jaw can cause permanent dry mouth, resulting in an increased number of dental caries and damage to the jawbone. Radiation to the lungs can cause lung inflammation (radiation pneumonitis). Very high doses can result in severe scarring (fibrosis) of lung tissue, which can cause disabling shortness of breath and later death. The heart and its protective sac (pericardium) can become inflamed after extensive radiation to the chest, causing symptoms such as chest pain and shortness of breath. High accumulated doses of radiation to the spinal cord can cause catastrophic damage, leading to paralysis, incontinence, and loss of sensation. Extensive radiation to the abdomen (for lymph node, testicular, or ovarian cancer) can lead to chronic ulcers, scarring, and narrowing or perforation of the intestine, causing symptoms such as abdominal pain, vomiting, vomiting blood, and dark, tarry stools.
Occasionally, severe injuries develop long after the completion of radiation therapy. Kidney function may decline 6 months to a year after people have received extremely large amounts of radiation, resulting in anemia and high blood pressure. High accumulated doses of radiation to muscles may cause a painful condition that includes muscle wasting (atrophy) and calcium deposits in the irradiated muscle. Occasionally, radiation therapy may result in a new cancerous (malignant) tumor. These radiation-induced cancers typically occur 10 or more years after exposure.
Exposure to radiation may be obvious from people's history. Radiation injury is suspected when people develop symptoms of illness or skin redness or sores after receiving radiation therapy or being exposed during a radiation accident. The time until symptoms develop can help doctors estimate the radiation dose. No specific tests are available to diagnose radiation exposure, although certain standard clinical tests may be used to detect infection, low blood counts, or organ malfunction. To help determine the severity of radiation exposure, doctors measure the number of lymphocytes (a type of white blood cell) in the blood. Typically, the lower the lymphocyte count 48 hours after exposure, the worse the radiation exposure.
Radioactive contamination, unlike irradiation, can be determined by surveying a person's body with a Geiger-Muller counter, a device that detects radiation. Swabs from the nose, throat, and any wounds also are checked for radioactivity.
The early symptoms of acute radiation illness–nausea, vomiting, and tremors–can also be caused by anxiety. Because anxiety is common after terrorist and nuclear incidents, people should not panic when such symptoms develop, particularly if the amount of radiation exposure is unknown and may have been small.
Following widespread high-level environmental contamination from a nuclear power plant accident or the intentional release of radioactive material, people should follow the advice of public health officials. Such information is usually broadcast on TV and radio. The advice may be for people to evacuate the contaminated area or to take shelter where they are. Whether evacuation or sheltering is recommended depends on many factors, including time elapsed since the initial release, whether the release has stopped, weather conditions, availability of adequate shelters, and road and traffic conditions. If sheltering is recommended, sheltering in a concrete or metal structure, particularly one below grade (such as in a basement), is best. Half way between the top and bottom of a tall building, near the center away from windows, is best when no below-grade shelter is available.
Changing clothes and showering are recommended if people suspect they may have been contaminated with radioactive material. People can obtain potassium iodide (KI) tablets from local pharmacies and some public health agencies. However, potassium iodide is only useful if radioactive iodine is released. It does not provide protection from other radioactive materials. People with known iodine sensitivity and certain thyroid conditions should avoid potassium iodide. A doctor should be consulted if iodine sensitivity is suspected.
During imaging procedures that involve ionizing radiation and especially during radiation therapy for cancer, which involves high doses, the most susceptible parts of the body, such as the lenses of the eyes, female breasts, ovaries or testes, and thyroid gland, are shielded when possible (for example, by wearing a lead-filled covering).
The outcome depends on the radiation dose, dose rate (how quickly the exposure occurs), and the parts of the body that are affected. Other factors include people's state of health and whether they receive medical care. In general, without medical care, half of all people who receive more than 3 Gy of whole-body radiation at once die. Nearly all people who receive more than6 Gy die. Nearly all of those who receive less than 2 Gy fully recover within 1 month, although long-term complications such as cancer may occur. With medical care, about half of people survive 6 Gy of whole-body radiation. Some people have survived doses of up to 10 Gy.
Because doctors are unlikely to know the amount of radiation a person has received, they usually predict outcome based on the person's symptoms. The cerbrovascular syndrome is fatal within hours to a few days. The gastrointestinal syndrome generally is fatal within 3 to 10 days, although some people survive for a few weeks. Many people who receive proper medical are survive the hematopietic syndrome, depending on the radiation dose and their state of health. Those who do not survive typically die within 4 to 8 weeks after exposure.
Physical injuries are treated before irradiation is treated because they are more immediately life-threatening. Irradiation has no emergency treatment, but doctors closely monitor people for the development of the various syndromes and treat the symptoms as they arise.
Contamination should be removed promptly to prevent the radioactive material from continuing to irradiate the person and to prevent the radioactive material from being taken up by the body. Contaminated wounds are treated before contaminated skin. Doctors decontaminate wounds by flushing them with a salt water solution and wiping them with a surgical sponge. After decontamination, wounds are covered to prevent recontamination as other sites are washed. Contaminated skin should be gently scrubbed with large amounts of soap and warm (not hot) water. Skin folds and nails need extra attention. Harsh chemicals, brushes, or scrubbing that may break the skin surface should be avoided. If hair cannot be decontaminated with soap and water, clipping it off with scissors is preferable to shaving. Shaving may cut the skin and allow contamination to enter the body. Skin and wound decontamination should continue until the Geiger-Muller counter shows that the radioactivity is gone or almost gone, until washing does not substantially reduce the amount of radioactivity measured, or until further cleaning risks damaging the skin. Burns should be gently rinsed but not scrubbed.
Certain measures can decrease internal contamination. If people have recently swallowed a significant amount of radioactive material, vomiting may be induced. Some radioactive materials have specific chemical treatments that can reduce their absorption after being swallowed or help speed their removal from the body. If administered shortly before or soon after internal contamination with radioactive iodine, potassium iodide very effectively prevents the thyroid gland from absorbing the radioactive iodine, thus reducing the risk of thyroid cancer and thyroid injury. Potassium iodide is effective only for radioactive iodine, not other radioactive elements. Other drugs, such as zinc or calcium diethylenetriamine penta-acetate (DTPA—for plutonium, yttrium, californium, and americium), calcium or aluminum phosphate solutions (for radioactive strontium), and Prussian blue (for radioactive cesium, rubidium, and thallium), can be given intravenously to remove a fraction of certain radionuclides after they have entered the body. However, except for potassium iodide, which is very effective, drugs given to reduce internal contamination reduce exposure by only about 25 to 75%.
Nausea and vomiting can be reduced by taking drugs to prevent vomiting (antiemetics). Such drugs are routinely given to people undergoing radiation therapy or chemotherapy. Dehydration is treated with fluids given intravenously.
People with the gastrointestinal or hematopoietic syndrome are kept isolated to minimize their contact with infectious microorganisms. Blood transfusions and injections of growth factors that stimulate blood cell production (such as erythropoietin and colony-stimulating factor) are given to increase blood counts. This treatment helps decrease bleeding and anemia and helps fight infections. If the bone marrow is severely damaged, these growth factors are ineffective, and sometimes bone marrow transplantation is done, although the experience with this treatment for this condition is limited and the success rate is low.
People with the gastrointestinal syndrome require antiemetics, fluids given intravenously, and sedatives. Some people may be able to eat a bland diet. Antibiotics are given by mouth to kill bacteria in the intestine that may invade the body. Antibiotics as well as antifungal and antiviral drugs also are given intravenously when necessary.
Treatment for the cerebrovascular syndrome is geared toward providing comfort by relieving pain, anxiety, and breathing difficulties. Drugs are given to control seizures.
Pain caused by radiation-induced sores or ulcers is treated with analgesics. If these wounds fail to heal satisfactorily over time they may be repaired surgically with skin grafts or other procedures.
Last full review/revision February 2009 by Jerrold T. Bushberg, PhD, DABMP