Large doses of ionizing radiation can cause acute illness by reducing the production of blood cells and damaging the digestive tract.
A very large dose of ionizing radiation can also damage the heart and blood vessels (cardiovascular system), brain, and skin.
Radiation injury due to large and very large doses is referred to as a tissue reaction. The dose needed to cause visible tissue injury varies with tissue type.
Ionizing radiation can increase the risk of cancer.
Radiation exposure of sperm and egg cells carries little increased risk of genetic defects in offspring.
Doctors remove as much external and internal (material that is inhaled or ingested) radioactive material as possible and treat symptoms and complications of radiation injury.
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 devices, such as x-ray and radiation therapy machines.
Radio waves, such as from cell phones and AM and FM radio 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.
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 dose levels are measured in mGy (1 mGy = 1/1000Gy) and mSv (1 mSv = 1/1000Sv).
An individual's radiation dose can be increased in two ways, 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, used, for example, to evaluate 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.
People are exposed constantly to low levels of radiation, naturally occurring (background) radiation, and intermittently to radiation from manufactured sources. Natural background radiation varies tremendously worldwide and within countries as well. In the United States, people receive on average about 3 mSv/yr from natural sources and the range of exposures varies from about 0.5 to 20 mSv/yr depending on the region, elevation above sea level, and local geology. On average, an additional 3 mSv/yr is received from manufactured (mostly medical) sources, making the total average per capita effective dose about 6 mSv/yr.
Sources of background radiation include
Cosmic and solar 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.
Even in total, the doses from natural background radiation are far too low to cause radiation injury. To date there have been no demonstrated health effects due to differences in the level of background radiation because the risks of radiation-induced health effects at these low exposure levels are either nonexistent or too small to be observed.
Most people’s exposure to sources of manufactured radiation involves medical imaging tests (particularly computed tomography [CT] and cardiac nuclear medicine scans). 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 manufactured sources, such as radiation accidents and fallout from previous 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, industrial radiography sources, and x-ray machines. Such workers may receive significant doses of radiation. These accidents are rare and typically 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. Radiation injuries have also occurred to patients receiving radiation therapy and certain medical procedures that are guided by a pulsed x-ray beam that shows a moving x-ray image on a screen (fluoroscopy). Some of these injuries to patients are the result of accidents or improper use but sometimes, in more complex cases, appropriate use of such procedures may cause unavoidable radiation-induced complications and tissue reactions.
On rare occasions, substantial amounts of radioactive material have been released from nuclear power plants, including the Three Mile Island plant in Pennsylvania in 1979, the Chernobyl plant in the Ukraine in 1986, and the Fukushima Daiichi plant in Japan in 2011. 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 an additional dose of about 0.08 mSv. However, the average dose to the approximately 115,000 people who were evacuated from the area near the Chernobyl plant was about 30 mSv. For comparison, the typical dose from a single CT scan is between 4 and 8 mSv. People working at the Chernobyl plant received significantly more. More than 30 workers and emergency responders died within a few months of the accident, and many more developed acute radiation sickness. There was low-level contamination from Chernobyl as far away as Europe, Asia, and even (to a lesser extent) in North America. The average cumulative radiation dose to populations living in areas with low-level contamination (various regions of Belarus, Russia, and Ukraine) over a 20-year period after the accident was estimated to be about 9 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 (3 mSv per year). Some workers at the Fukushima Daiichi plant were exposed to significant doses of radiation; however, there were no deaths or permanent radiation-induced tissue reactions. People living within 12 miles (20 kilometers) of the Fukushima Daiichi plant were evacuated because of concerns about radiation exposure. However, estimates are that almost no nearby residents received more than about 5 mSv. The World Health Organization predicts that cancer deaths related to this accident will be low.
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 due to 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 (see Radiological Weapons) 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.
Annual Radiation Exposure in the United States
The damaging effects of radiation (that is, the severity of the tissue reaction) depend on several factors:
The amount (dose)
How rapidly the dose is received
How much of the body is exposed
The sensitivity of particular tissues to radiation
The presence of genetic abnormalities that impair normal DNA repair
The person's age at time of exposure
The person's general state of health prior to the exposure
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 can be fatal when the radiation dose is to the entire body. However, when limited to a small area 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.
In children, some organs and tissues such as the brain, lens of the eye, and thyroid gland, are more sensitive to radiation than in adults. However, some tissues in children are no more sensitive to radiation than in adults, and some, such as the ovaries, are actually less sensitive. The reasons for the differences are complicated and not completely understood, but doctors think that the higher sensitivity of some tissues in children is due, at least in part, to the fact that children's cells grow and mature more quickly and will undergo many more cell divisions than those in adults.
The fetus is sensitive to damage from radiation because fetal cells are dividing very quickly and also differentiating from immature into mature cells. 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 low doses used in imaging tests that a pregnant woman might typically undergo, there is no apparent increase beyond the normal risk of having a child born with a birth defect.
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 might think. Even a whole-body dose of 500 mGy (over 150 times more than the average annual background radiation dose) increases a typical person’s lifetime risk of dying from cancer from 22% to about 24.5%, only a 2.5% absolute risk increase.
In a fetus or child, the risk of radiation-induced cancer is several times higher than in an adult. 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 dying as a result of cancer for a 1-year-old who has a computed tomographic (CT) scan of the abdomen may be increased by about 0.1%. Recently, concerns about the possible risks due to CT scans have led to controversy about whether CT scans are being used too often. Because of these concerns, CT scan techniques are being optimized to reduce the radiation dose. Doctors also try to do a CT scan only when it is more accurate than other tests that use less or no radiation. When CT is clearly the most accurate test, the risk resulting from not making the correct diagnosis because a less accurate test was used is much greater than the risk of the CT scan.
In animals, high doses of radiation of the ovaries or testes have 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 bomb explosions in Japan. It may be that the radiation exposure was not high enough to cause a measurable increase. No increase in the risk of birth defects is found in children conceived after their parents received radiation therapy for cancer where the average dose to the ovaries was about 0.5 Gy and to the testes was about 1.2 Gy (typical exposure to tissues next to but not directly in the treatment area during radiation therapy).
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 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 illness into three groups (syndromes) 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 can often estimate a person’s radiation exposure based on the timing, nature, and severity of the early symptoms. However, the presence of injuries, burns, or severe anxiety can complicate this estimate.
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 during physical exertion. If people survive, after 4 to 5 weeks, blood cells begin to be produced once more, but people feel weak and tired for months, and they have an increased risk of cancer.
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, causing 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.
Radiation therapy for cancer is one of the most common causes of local radiation injuries. Symptoms depend on the amount of radiation, the rate at which it is received, 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 often 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. Halfway 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. Certain experimental drugs given during or immediately after irradiation have been shown to increase survival rates in animals. However, these drugs can be very toxic and are not currently recommended for people.
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 one time die. Nearly all people who receive more than 8 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 cerebrovascular 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 care survive the hematopoietic 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.
Serious 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 warm (not hot) water and soap. 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 or by mouth 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 hematopoietic stem cell transplantation is done, although experience with stem cell transplantation for either gastrointestinal or hematopoietic syndrome 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.
People who survive may need regular monitoring for cataracts and thyroid disorders, but no other regular monitoring is needed.