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Ionizing radiation injures tissues variably depending on the type of radiation and amount and extent of exposure. Symptoms may be local (eg, burns) or systemic (eg, acute radiation sickness). Diagnosis is by history of exposure and sometimes use of Geiger or alpha counters. Treatment is by reverse isolation and (when indicated) decontamination but is otherwise largely supportive. Uptake inhibitors or chelating agents may be useful for treatment of internal contamination with specific radionuclides. Prognosis is estimated by measuring the lymphocyte count during the initial 24 to 72 h.

Radiation refers to high-energy electromagnetic waves (x-rays, gamma rays) or particles (alpha particles, beta particles, neutrons) emitted by radioactive elements or man-made sources (eg, x-ray and radiation therapy equipment).

Alpha particles are helium nuclei emitted by various radionuclides (eg, plutonium, radium, uranium) that cannot penetrate skin beyond a shallow depth (< 0.1 mm). Beta particles are high-energy electrons that are emitted from the nuclei of unstable atoms (eg, cesium-137, iodine-131). These particles can penetrate more deeply into skin (1 to 2 cm) and cause both epithelial and subepithelial damage. Neutrons are electrically neutral particles ejected from the nucleus of some radioactive atoms and produced in nuclear reactions (eg, reactors, linear accelerators); they can penetrate deeply into tissues (> 2 cm), where they collide with stable atoms, resulting in emission of alpha and beta particles and gamma radiation. Gamma radiation and x-rays are high-energy electromagnetic radiation (ie, photons) that can travel many centimeters into human tissue.

Because of these characteristics, alpha and beta particles cause the most damage when radioactive elements that emit them are within (internal contamination) or directly on the body; only tissue in close proximity to the element is affected. Gamma rays and x-rays can cause damage at a great distance from their source and are typically responsible for acute radiation syndromes (see Radiation Injury: Acute radiation syndromes).

Measurement: Units of measurement include the roentgen, gray, and sievert. The roentgen (R) represents the intensity of x- or gamma radiation in air. The gray (Gy) is the amount of that energy absorbed by tissue. Because biologic damage per Gy varies with radiation type (it is higher for neutrons and alpha particles), the dose in Gy is corrected by a quality factor; the resulting unit is the sievert (Sv). The Gy and Sv have replaced the rad and rem (Gy = 100 rad; Sv = 100 rem) in current nomenclature and are essentially equal when describing gamma or beta radiation.

Exposure: The 2 main types of radiation exposure are contamination and irradiation. Many radiation incidents involve both.

Contamination is contact with and retention of radioactive material, usually as a dust or liquid. External contamination is on skin or clothing, from which it can fall or be rubbed off, contaminating other people and objects. Radioactive material also can be absorbed through the lungs, GI tract, or breaks in the skin (internal contamination). Absorbed material is transported to various sites in the body (eg, bone marrow), where it continues to release radiation until it is removed or decays. Internal contamination is more difficult to remove.

Irradiation is exposure to penetrating radiation but not radioactive material (ie, no contamination is involved). Typically, gamma rays and x-rays are involved. Irradiation can involve the whole body, which can result in systemic symptoms and radiation syndromes (see Radiation Injury: Acute radiation syndromes), or a small part of the body (eg, from therapeutic radiation), which can result in focal symptoms.

Sources: People are constantly exposed to low levels of natural radiation (background radiation). Background radiation includes cosmic radiation, much of which is blocked by the atmosphere; thus, exposure is greater for people living at high altitudes and during airplane flights. Radioactive elements, particularly radon gas, are also present in many rocks and minerals. These elements end up in various substances, including food and construction materials. Radon exposure typically accounts for about ²⁄₃ of the total dose of naturally occurring radiation.

People are also exposed to radiation from man-made sources, including from nuclear weapons (eg, during testing) and various medical tests and treatments. The average person receives a total of about 3 to 4 mSv/yr from natural and man-made sources (see Table 1: Radiation Injury: Average Annual Radiation Exposure in the US).

Table 1
Average Annual Radiation Exposure in the US Source Dose (millisieverts) Naturally occurring sources Radon gas     2.00 Other terrestrial sources     0.28 Radiation from outer space     0.27 Natural internal radioactive elements     0.39 Subtotal     2.94 Man-made sources Diagnostic x-rays (for average person)     0.39 Nuclear medicine     0.14 Consumer products     0.10 Fallout from weapons testing < 0.01 Nuclear industry < 0.01 Subtotal     0.63 Total Annual Exposure     3.6 Other sources of exposure Airline travel         0.005/h of flight Dental x-rays     0.09 Chest x-ray     0.10 Barium enema     8.75

Radiation has escaped from nuclear power plants, including the Three Mile Island plant in Pennsylvania in 1979 and at Chernobyl in Ukraine in 1986. Exposure from Three Mile Island was minimal; people living within 1.6 km of the plant received only about 0.08 mSv. However, people living near the Chernobyl plant were exposed to about 430 mSv of radiation. More than 30 people died, many more were injured, and radiation from that accident reached other parts of Europe, Asia, and the US. In total, excluding Chernobyl, radiation exposure from reactors in the first 40 yr of nuclear energy use has resulted in 35 serious exposures with 10 deaths, none of which were associated with commercial power plants. Other significant events include the detonation of the atomic bombs over Japan in August 1945, which caused > 100,000 deaths from the immediate blast and hundreds of thousands more deaths from radiation illness and other associated injuries.

Intentional radiation exposure through terrorist activities is a concern. Possible scenarios range from limited dispersal of radioactive substances without explosives to dispersal using conventional explosives (“dirty bombs”) to attacks on nuclear reactors and detonation of nuclear weapons.

Pathophysiology

Ionizing radiation damages mRNA, DNA, and proteins directly and by generation of highly reactive free radicals. Large doses of ionizing radiation cause cell death, whereas lower doses interfere with cell proliferation. Damage to other cellular components can result in progressive hypoplasia, atrophy, and eventually fibrosis. Genetic damage may result in malignant transformation or a transmissible genetic defect.

Tissues that normally undergo continual and rapid renewal are particularly vulnerable to radiation. Most sensitive are lymphoid cells, followed by (in descending order) gonads, proliferating bone marrow cells, intestinal epithelial cells, epidermis, hepatic cells, epithelium of lung alveoli and biliary passages, kidney epithelial cells, endothelial cells (pleura and peritoneum), nerve cells, bone cells, and muscle and connective tissue cells.

The precise dose at which toxic effects occur depends on the time course of exposure, ie, a single rapid dose of several Gy is more damaging than the same dose given over weeks or months. Dose response also depends on the amount of body area exposed. Significant illness is certain, and fatalities occur after whole-body irradiation with > 4.5 Gy; however, 10s of Gy can be tolerated well when delivered over a long period to a small area of tissue (eg, for cancer therapy).

Children are more susceptible to radiation injury because they have a higher rate of cellular proliferation and a higher number of future cell divisions.

Symptoms and Signs

Manifestations depend on whether radiation exposure involves the whole body (acute radiation syndrome) or a focal area.

Acute radiation syndromes: Several distinct syndromes occur after whole-body radiation. These syndromes have 3 different phases: a prodromal phase (0 to 2 days after exposure) with lethargy, nausea, and vomiting; a latent asymptomatic phase (1 to 20 days after exposure); and a phase of overt systemic illness (2 to 60 days after exposure) classified by the main organ system affected. The higher the radiation dose, the more severe and rapid is the progression. The symptoms and time course are fairly consistent for a given dose of radiation; thus, they can be used to estimate the radiation exposure.

The cerebral syndrome, produced by extremely high whole-body doses of radiation (> 10 Gy), is always fatal. The prodrome develops within minutes to 1 h of exposure. There is little or no latent phase, and patients develop tremors, seizures, ataxia, cerebral edema, and death within hours to 1 or 2 days.

The GI syndrome is produced by whole-body doses of ≥ 4 Gy and is dominated by effects on the GI tract. Prodromal symptoms, often marked, develop within 2 to 12 h and resolve within 2 days. During the latent period of 4 to 5 days, GI mucosal cells die; cell death is followed by intractable nausea, vomiting, and diarrhea, which lead to severe dehydration and electrolyte imbalances, diminished plasma volume, and vascular collapse. Bowel necrosis may also occur, predisposing to bacteremia and sepsis. Death is common. Survivors also have the hematopoietic syndrome.

The hematopoietic syndrome is produced by whole-body doses of > 2 Gy. A mild prodrome may begin after 6 to 12 h, lasting 24 to 36 h. Bone marrow cells are affected immediately, resulting initially in lymphopenia (maximal within 24 to 36 h). However, the patient remains asymptomatic during a latent period of > 1 wk as marrow production falls. Various infections result from neutropenia (most prominent at 2 to 4 wk) and decreased antibody production, and petechiae and mucosal bleeding result from thrombocytopenia, which develops within 3 to 4 wk and may persist for months. Anemia develops slowly, because preexisting RBCs have a longer lifespan than WBCs and platelets. Survivors have an increased incidence of leukemias.

Focal injury: Radiation to nearly any organ can produce both acute and chronic adverse effects. In most patients, these adverse effects result from therapeutic radiation (see Table 2: Radiation Injury: Focal Radiation Injury*; see Principles of Cancer Therapy: Radiation Therapy).

Table 2
Focal Radiation Injury* Tissue Exposed Adverse Effects Brain See Intracranial and Spinal Tumors: Radiation Therapy and Neurotoxicity Cardiovascular Chest pain, radiation pericarditis, radiation myocarditis Dermatologic Local erythema with intense burning or tingling, xerosis, keratosis, telangiectasis, vesiculation, hair loss (within 5 to 21 days of exposure) Dose > 5 Gy: Wet gangrene, ulceration Long-term effects: Progressive fibrosis, squamous cell carcinoma Gonads Dose ≤ 0.01 to 0.015 Gy: Depressed spermatogenesis, amenorrhea, decreased libido Dose 5–6 Gy: Sterility Head and neck Mucositis, odynophagia, thyroid carcinoma Musculoskeletal Myopathy, neoplastic changes, osteosarcoma Ophthalmic Dose 0.2 Gy: Cataract Pulmonary Radiation pneumonitis Dose > 30 Gy: Sometimes-fatal pulmonary fibrosis Renal Decreased GFR, decreased renal tubular function High doses (6 mo to 1 yr latent period): Proteinuria, renal insufficiency, anemia, hypertension Cumulative dose > 20 Gy in < 5 wk: Radiation fibrosis, oliguric renal failure Spinal cord Dose > 50 Gy: Myelopathy, neurologic dysfunction Fetus Growth restriction, congenital malformations, in-born errors of metabolism, cancer, fetal demise *Typically from therapeutic radiation.

Diagnosis

After acute radiation exposure, laboratory evaluation includes blood chemistries, urinalysis, and CBC with differential. Type and compatibility testing and blood for HLA typing should be obtained in the event that transfusion or hematopoietic stem cell transplantation is necessary. The lymphocyte count should be obtained 24, 48, and 72 h after exposure to estimate the initial radiation dose and prognosis (see Table 3: Radiation Injury: Relationship Between Lymphocyte Count at 48 h, Radiation Dose,* and Prognosis). CBC is repeated weekly to monitor marrow activity and as needed based on the clinical course.

Table 3
Relationship Between Lymphocyte Count at 48 h, Radiation Dose,* and Prognosis Lowest Lymphocyte Count (cells/ML) Radiation Dose (Gy) Prognosis 1500 (normal) 0.4 Excellent 1000–1499 0.5–1.9 Good 500–999 2.0–3.9 Fair 100–499 4.0–7.9 Poor < 100 8.0 Almost always fatal *Whole-body irradiation (approximate dose). Adapted from Mettler FA Jr, Voelz GL: Major radiation exposure—what to expect and how to respond. New England Journal of Medicine 346:1554–1561, 2002.

Contamination: When radionuclides are involved, the entire body is surveyed with a Geiger counter to identify external contamination. Additionally, to detect possible internal contamination, the nares, ears, mouth, and wounds are wiped with moistened swabs that are then tested with the counter. Urine, feces, and emesis should also be tested for radioactivity.

Prognosis

Without medical care, the LD₅₀ (dose fatal to 50% of patients within 60 days) for whole-body radiation is about 4 Gy; ≥ 6 Gy exposure is nearly always fatal. With < 6 Gy, survival is possible and is inversely related to total dose. Time to death is also inversely proportional to dose (and hence symptoms). Death results within hours to a few days in the cerebral syndrome and usually within 3 to 10 days in the GI syndrome. In the hematopoietic syndrome, death may occur within 2 to 4 wk because of a supervening infection or within 3 to 6 wk because of massive hemorrhage. Patients exposed to whole-body doses < 2 Gy should fully recover within 1 mo, although long-term sequelae (eg, cancer) may occur.

With medical care, the LD₅₀ is about 6 Gy and occasional patients have survived up to 10 Gy.

Treatment

Radiation exposure may be accompanied by physical injuries (eg, from blast or fall); associated trauma is more immediately life threatening than radiation exposure and must be treated expeditiously (see Approach to the Trauma Patient: Evaluation and Treatment). Trauma resuscitation of the seriously injured must not be delayed awaiting special radiation management equipment and personnel. Standard universal precautions as routinely used in trauma care adequately protect the resuscitation team.

Hospitalization: Accrediting agencies mandate that all hospitals have protocols and that personnel have training to deal with radioactive contamination. Identification of radioactive contamination on a patient should prompt his isolation in a designated area, decontamination, and notification of the hospital radiation safety officer, public health officials, hazardous material teams, and law enforcement agencies as appropriate to investigate the source of radioactivity.

Treatment area surfaces may be covered with plastic sheeting to aid in facility decontamination; this preparation should never take precedence over provision of medical stabilization. Waste receptacles (labeled “Caution, Radioactive Material”), sample containers, and Geiger counters should be readily available. All equipment that has come into contact with the room or with the patient (including ambulance equipment) should remain isolated until lack of contamination has been verified.

Personnel should wear caps, masks, gowns, gloves, and shoe covers, and all openings in protective gear should be sealed with tape. Used gear should be placed in specially marked bags or containers. Dosimeter badges should be worn to monitor radiation exposure. Personnel may be rotated to minimize exposure, and pregnant personnel should be excluded from the treatment area.

Decontamination: After isolation in the designated area, clothes are removed carefully to minimize the spread of contamination and placed in appropriately marked containers. Clothing removal eliminates about 90% of external contamination. Contaminated skin surface is washed with lukewarm water and mild detergent until radioactivity counts are equal to about 2 times background or until successive washings do not significantly reduce contamination levels. All wounds are covered during washing to prevent the introduction of radioactive material. Scrubbing may be firm but should not abrade the skin. Special attention is usually required for fingernails and skinfolds. Special chelating solutions containing ethylenediaminetetraacetic acid are not necessary.

Wounds are checked with Geiger counters and irrigated until counts normalize; debridement is sometimes necessary to remove embedded material. Foreign bodies should be disposed of in lead containers.

Ingested radioactive material should be removed promptly by induced vomiting or lavage if exposure is recent. Frequent mouth rinsing with saline or dilute hydrogen peroxide is indicated for oral contamination. Eye exposure should be decontaminated by directing a stream of water or saline laterally to avoid contaminating the nasolacrimal duct.

Other, more specific measures to reduce internal contamination depend on the specific radionuclide involved; consultation with a specialist is recommended. If there is exposure to radioiodine (which should be presumed after a reactor incident or nuclear detonation), the patient should be given K iodide (KI) as soon as possible; its effectiveness diminishes significantly within several hours after exposure. KI can be given either in tablet form or as a supersaturated solution (dosage: adult, 130 mg; age 3 to 18 yr, 65 mg; age 1 to 36 mo, 32 mg; age < 1 mo, 16 mg). Various chelating agents are available for treating internal contamination with other radioactive substances: supersaturated K (radioactive iodine), Ca or zinc diethylenetriamine penta-acetate (plutonium-239 or yttrium-90), Prussian blue (cesium-137, rubidium-82, thallium-201), or oral Ca or aluminum phosphate solutions (radioactive strontium).

Decontamination is not necessary for patients who have been irradiated by an external source and are uncontaminated.

Specific management: Symptomatic treatment is given as needed and includes managing shock and anoxia, relieving pain and anxiety, and giving sedatives ( lorazepam Some Trade Names
ATIVAN
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1 to 2 mg IV prn) to control seizures, antiemetics ( metoclopramide Some Trade Names
REGLAN
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10 to 20 mg IV q 4 to 6 h; prochlorperazine Some Trade Names
COMPAZINE
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5 to 10 mg IV q 4 to 6 h; ondansetron Some Trade Names
ZOFRAN
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4 to 8 mg IV q 8 to 12 h) to control vomiting, and antidiarrheal agents (kaolin/pectin 30 to 60 mL po with each loose stool; loperamide Some Trade Names
IMODIUM
Click for Drug Monograph
4 mg po initially, then 2 mg po with each loose stool) for diarrhea.

There is no specific treatment for the cerebral syndrome. It is universally fatal; care should address patient comfort.

The GI syndrome is treated with aggressive fluid resuscitation and electrolyte replacement. Parenteral nutrition should be initiated to promote bowel rest. If the patient is febrile, broad-spectrum antibiotics (eg, imipenem 500 mg IV q 6 h) should be initiated immediately. However, septic shock from overwhelming infection remains the most likely cause of death.

Management of the hematopoietic syndrome is similar to that of marrow hypoplasia and pancytopenia of any cause (see Anemias Caused by Deficient Erythropoiesis: Aplastic Anemia). Blood products should be transfused to treat anemia and thrombocytopenia, and hematopoietic growth factors (granulocyte colony-stimulating factor and granulocyte macrophage colony-stimulating factor) and broad-spectrum antibiotics should be given to treat neutropenia and neutropenic fever, respectively (see Neutropenia and Lymphocytopenia: Treatment). Neutropenic patients should also be placed in reverse isolation. With radiation doses > 4 Gy, the probability of bone marrow recovery is poor, and hematopoietic growth factors should be given as soon as possible. Stem cell transplants have had limited success but should be considered for exposure > 7 to 8 Gy (see Transplantation: Hematopoietic Stem Cell Transplantation).

Aside from regular monitoring for signs of disease (eg, ophthalmic examination for cataracts, thyroid function studies for thyroid disease), there is no specific monitoring or treatment for specific organ injury. Radiation-induced cancer is treated in the same way as a similar spontaneous cancer.

Prevention

Protection from radiation exposure is accomplished through minimizing the time of exposure, maximizing the distance from the source, and using shielding. Shielding from a known discrete radioactive source can be reasonably achieved (eg, with lead aprons or commercially available transparent shields); however, shielding from most radionuclide contamination from large-scale disasters (eg, nuclear accident or attack) is not feasible. Thus, if at all possible after radiation release, evacuation of the area of exposure should be undertaken, with evacuation lasting 1 wk if the anticipated dose is > 0.05 Gy and permanent resettlement if the lifetime dose is expected to be > 1 Gy. When evacuation is not possible, taking shelter in a concrete or metal structure (eg, basement) can confer some protection.

People living within 16 km (10 miles) of a nuclear power plant should have ready access to KI tablets. These can be obtained from local pharmacies and some public health agencies. Many drugs and chemicals (eg, sulfhydryl compounds) increase survival rate in animals if given before irradiation. However, none are practical for humans.

All personnel working with radioactivity should wear dosimeter badges and be monitored for signs of excessive radiation exposure. The standard occupational limit is 0.05 Gy/yr. For emergency medical personnel, recommended dosage limits include 0.05 Gy for any non-lifesaving events and 0.25 Gy for any lifesaving event.

Last full review/revision November 2005

Content last modified March 2007