Topic Resources
Radiation injury is damage to tissues caused by exposure to ionizing radiation.
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Large doses of ionizing radiation can cause acute illness by reducing the production of blood cells and damaging the digestive tract.
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A very large dose of ionizing radiation can also damage the heart and blood vessels (cardiovascular system), brain, and skin.
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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.
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Ionizing radiation can increase the risk of cancer.
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Radiation exposure of sperm and egg cells carries little increased risk of genetic defects in offspring.
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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.
Radiation Sickness
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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.
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 dose levels are measured in mGy (1 mGy = 1/1000Gy) and mSv (1 mSv = 1/1000Sv).
Contamination vs. irradiation
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.
Sources of Radiation Exposure
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.
Background radiation
Sources of background radiation include
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Solar and cosmic radiation from space
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Naturally occurring radioactive elements in the earth
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.
Man-made radiation
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.
Effects of Radiation
The damaging effects of radiation (that is, the severity of the tissue reaction) depend on several factors:
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The amount (dose)
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How rapidly the dose is received
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How much of the body is exposed
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The sensitivity of particular tissues to radiation
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The presence of genetic abnormalities that impair normal DNA repair
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The person's age at time of exposure
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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.
Radiation and children
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.
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
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.
Radiation and inherited defects
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
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 illness into
three groups (syndromes) based on the main organ system affected,
although there is overlap among these groups:
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Hematopoietic syndrome: Affects tissues that produce blood cells
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Gastrointestinal syndrome: Affects the digestive tract
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Cerebrovascular syndrome: Affects the brain and nervous system
Acute radiation illness usually progresses through three stages:
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Early symptoms such as nausea, loss of appetite, vomiting, tiredness and, when very high radiation doses are received, diarrhea (collectively called the prodrome)
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A symptom-free period (latent stage)
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Various patterns of symptoms (syndromes), depending on the amount of radiation received
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.
Local radiation injury
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.
Diagnosis
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Symptoms, severity of symptoms, and time to onset of symptoms after exposure to radiation
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Lymphocyte counts (to determine severity of 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.
Prevention
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).
Prognosis
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.
Treatment
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Treatment of serious, life-threatening injuries first
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Decontamination of wounds, skin, and hair
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Treatment of internal contamination
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Sometimes specific measures for particular radionuclides
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Treatment of compromised immune system
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Supportive care
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.
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