Acute radiation syndrome occurs when the body absorbs a high dose of ionizing radiation within minutes, whether from a nuclear accident, an atomic explosion or exposure to a radioactive source. From dose-dependent symptoms and stages to diagnosis and treatment, here is what you need to know about this potentially fatal condition.
1. What is acute radiation syndrome?
Acute radiation syndrome (ARS) refers to the set of potentially fatal disorders that occur when the whole body, or a large portion of its tissues, absorbs a high dose of ionizing radiation (alpha, beta, X or gamma rays, neutron flux) over a short period of time, often just a few minutes. It involves damage to multiple organs. Its severity depends on the absorbed dose (measured in grays, Gy) and how that dose is distributed in the body, on the duration of exposure and on the type of radiation.
Since natural background radiation is low, ARS is always the result of human activity: nuclear accidents in a laboratory or power plant, atomic explosions, or exposure to a powerful radioactive source (such as a medical source).
The central mechanism of ARS is DNA damage, which leads to cell death. Stem cells, which renew the body’s tissues, are particularly vulnerable. The bone marrow is affected first, followed by the digestive lining and the skin. The central nervous system is structurally resistant, but it is disrupted by exposure to very high doses.
Irradiated volume and fractionation are decisive. The irradiated volume is the amount of tissue exposed. A high dose concentrated on a small area spares the other organs, which keep functioning and can compensate for the damage.
In radiotherapy, for example, a tumor may receive from 50 to more than 70 Gy. The dose is targeted and fractionated, generally into sessions of 2 Gy. Fractionation means splitting the dose into several parts, so that healthy cells can repair some of the DNA damage between sessions. A dose spread over several weeks is better tolerated than one received all at once, as in an accident.
Before a bone marrow transplant, total body irradiation amounts to 10 to 12 Gy, fractionated over several sessions. By contrast, a single accidental exposure of more than 6 Gy can be fatal if it is not followed by intensive care.
2. Symptoms and progression of ARS
2.1. Stages of symptom progression
The first symptoms appear within minutes or hours of exposure: nausea, vomiting, diarrhea, loss of appetite, fatigue, skin redness and dizziness. The earlier and more intense they are, the higher the dose received.
A latent phase follows, during which symptoms subside or even disappear. It lasts from a few hours to a few weeks, and the higher the dose, the shorter it is.
Then comes the manifest illness phase: symptoms return and worsen over several weeks, with a risk of death. If the patient survives, recovery can take from several months to one or two years.
Long-term effects may also appear years later: cataracts, infertility, cardiovascular disease, and an increased risk of cancer.
2.2. Forms of ARS by dose received
Acute radiation syndrome takes different forms depending on the dose received and the sensitivity of the tissues involved. The main forms are described below.
Hematopoietic syndrome appears above roughly 1 Gy. It affects the bone marrow, which produces blood cells. This production drops or stops. The result is a high risk of infection (from fewer white blood cells), bleeding (from fewer platelets) and anemia (from fewer red blood cells).
Gastrointestinal syndrome occurs above roughly 6 Gy and is always accompanied by hematopoietic syndrome. The destruction of the intestinal lining causes abdominal pain, diarrhea, sometimes gastrointestinal bleeding, and the passage of bacteria into the bloodstream, with a risk of sepsis. Death can occur within one to two weeks.
Neurovascular syndrome develops above roughly 20 Gy and causes death within a few days. It combines a collapse in blood pressure with damage to the nervous system: disorientation in time and space, loss of coordination, seizures, then coma. These disorders are caused by cerebral edema and raised intracranial pressure.
The skin can also be severely affected, with radiation burns that add to the other injuries. Above 6 to 8 Gy, several organs are damaged at once (bone marrow, intestine, lungs, kidneys, skin). This multiple organ failure is very difficult to treat, and the prognosis becomes very poor.
3. Prevention and treatment of ARS
Prevention and diagnosis of radiation exposure
Prevention rests first on controlling radiation sources: the safety of nuclear facilities, oversight of industrial and medical sources, and measures against their loss or theft. For people who work near these sources, it also relies on radiation protection: limiting exposure time, keeping a distance from the source and using shielding.
After exposure, the dose received is the main factor determining severity. Early diagnosis, however, makes it possible to start appropriate treatment in time. As soon as radiation exposure is suspected, repeated blood tests track the drop in blood cells, starting with lymphocytes. The speed of this drop, along with the time it takes for the first symptoms to appear, gives an initial estimate of the dose. Analysis of lymphocyte chromosomes, which radiation damages in recognizable ways, refines this estimate. Finally, reconstructing the accident shows which parts of the body were most exposed, which guides treatment.
Treatment
When the bone marrow no longer produces enough blood cells, antibiotics, antifungals and antivirals prevent infections, and transfusions make up for the shortage of red blood cells and platelets. If some areas of the marrow were spared, drugs that stimulate blood cell production help them take over. If the marrow is completely destroyed, stem cells from a donor can be transplanted. This remains a last resort, because these cells may attack the recipient’s body.
Intestinal damage has no specific treatment. Fluid and electrolyte losses are replaced, diarrhea and vomiting are relieved, and the patient is fed intravenously. Above a certain dose threshold, this damage is irreversible and the prognosis remains very poor.
Deep radiation burns often require surgery. Stem cells taken from the patient’s own bone marrow and multiplied in the laboratory can also be injected into them to speed up healing.
Research is focusing on stem cells modified to avoid rejection and suit as many recipients as possible, as well as on ways to store them so that they are ready for use as soon as an accident occurs. Beyond radiation injury, this work also benefits regenerative medicine.
4. Examples of ARS
Nuclear explosions
Nuclear explosions are the best-known cause of ARS, particularly following the bombings of Hiroshima and Nagasaki (August 1945) and the long struggle of the hibakusha. Between 5% and 15% of deaths are attributed to ARS, with mortality peaking between September and December 1945.
In 1954, the US hydrogen bomb test in the Marshall Islands produced more radioactive fallout than expected. The crew of a Japanese fishing vessel located 140 km away was hospitalized, and one of the sailors died. In addition, sixty-four residents of Rongelap Atoll received approximately 1.6 Gy before being evacuated.
Nuclear reactor accidents
A few accidents have occurred at nuclear reactors around the world since 1958, exposing operators who developed ARS. However, it was the explosion of the Chernobyl reactor in 1986 that made the public aware of this risk. The disaster caused ARS in 200 plant workers and firefighters, 28 of whom died.
Lost or stolen radioactive sources
Between 1945 and 2000, worldwide, ten accidents involving a lost or stolen radioactive source led to ARS among members of the public, causing a total of 23 deaths.
Medical radiation
Radiotherapy illustrates the controlled side of radiation exposure. High doses are tolerated because the irradiated volume and the distribution of the dose over time are controlled.
5. Frequently asked questions
What are the first symptoms of acute radiation syndrome?
The first signs appear within minutes or hours of exposure: nausea, vomiting, diarrhea, loss of appetite, fatigue, skin redness and dizziness. The earlier and more intense these symptoms are, the higher the dose received. They may then fade during a misleading latent phase, before returning and worsening during the manifest illness phase, which can last several weeks.
What dose of radiation is fatal?
A single accidental exposure of more than 6 Gy can be fatal without intensive care. Above 1 Gy, the bone marrow is affected; above 6 Gy, the intestinal lining is destroyed and death can occur within one to two weeks; above 20 Gy, damage to the nervous system causes death within a few days. Fractionation and irradiated volume strongly change how well a dose is tolerated.
Can you recover from acute radiation syndrome?
Yes, depending on the dose received. Antibiotics, antivirals, antifungals, transfusions and drugs that stimulate the bone marrow can help patients through the critical phase. A donor stem cell transplant may be attempted as a last resort. Survivors can take several months to two years to recover, and face a risk of late effects such as cataracts, infertility, cardiovascular disease and cancer.
Why doesn’t radiotherapy cause acute radiation syndrome?
In radiotherapy, a tumor may receive from 50 to more than 70 Gy, but the dose is targeted at a small volume and split into sessions of about 2 Gy. Between sessions, healthy cells repair some of the DNA damage, and the spared organs keep functioning. Controlling both the irradiated volume and the timing makes these high doses tolerable.