Physical Principles

There are several common forms of ionizing radiation. Gamma rays and x-rays easily penetrate body tissues and deposit their energy deep in the body. Alpha-emitting radionuclides are hazardous only when they are inhaled, ingested, or deposited in an open wound, because alpha particles penetrate less than 0.1 mm in tissue. Beta particles (electrons) can penetrate to a depth of a few centimeters.

The radiation dose of interest for assessing health effects is the dose absorbed by specific tissues, measured in rads. The international unit of measurement for the absorbed dose, the gray (Gy), is equal to 100 rad. Since various forms of radiation (e.g., gamma rays and alpha particles) have different biologic effects at the same absorbed dose, the effective dose should be used for comparisons. The conventional unit of measurement for the effective dose is the rem. The international unit, the sievert, is equal to 100 rem. For practical purposes, a gray and a sievert are essentially equal when one is dealing with gamma and beta rays.

Important factors in minimizing the effects of radiation are time, distance, and shielding. Since the absorbed dose is directly proportional to time, only the minimal necessary amount of time should be spent in the vicinity of a radioactive source. The absorbed dose decreases rapidly with the square of the distance from the source. Tripling the distance from the source decreases the dose rate to one ninth. Shielding with lead can be used as protection from small radioactive sources. Staying indoors may be necessary for protection from a radioactive atmospheric plume.

Radioactivity decays with time. Some radionuclides (e.g., iodines) are short-lived, whereas others (e.g., cesium, strontium, and cobalt) have physical half-lives of many years. The cumulative dose depends not only on the dose rate measured at a point in time, but also on the duration of exposure and the rate of decay. The decay rate may affect some management decisions, such as whether to decontaminate the affected area or simply to let the radionuclide decay.

Biologic Principles

At high doses of radiation, some parenchymal cells die, but the clinical effect may be insignificant if the cells are not critical for survival. However, if a large number of cells are killed or if those that die are essential for survival, clinical symptoms develop.In general, rapidly dividing cells (e.g., intestinal-mucosa and bone marrow cells) are most vulnerable to radiation. At doses of less than 1.0 Gy, the damage is generally not severe, and the majority of cells survive, but they may be susceptible to subsequent malignant transformation. In this article, we do not review the long-term effects of radiation exposure (carcinogenesis), except to note that the probability of radiation-induced cancer is dose-related. Leukemia can develop as early as two years after exposure, whereas radiation-induced solid tumors may develop after a period of 5 to 10 years or even several decades.

Types of Radiation Exposure

Radiation accidents can result in localized or whole-body exposure and in internal or external deposition of radioactive materials (contamination). The clinical manifestations of exposure to radiation depend on the extent of penetration and the absorbed dose in various tissues. Recognition of acute radiation injuries is based on the history and clinical findings.Most radiation injuries do not constitute a medical emergency; management consists of the treatment of symptoms and supportive care.

Localized Exposure

Localized, deep exposure to radiation is caused by direct handling of highly radioactive sources. The patient often survives even if the absorbed doses are very high. Because the dose rate drops rapidly as the distance from the radioactive sources increases, systemic manifestations are not as severe as the local injury.

The signs of a radiation burn are similar to those of a thermal burn: erythema and desquamation or blistering. However, the signs of a radiation burn appear after a period of days (Table 2). Vascular insufficiency can develop several months or years later, causing ulceration or necrosis of tissues that had previously healed. Treatment of localized radiation injuries usually involves prophylaxis against infection, control of pain, and vasodilator therapy; in some cases, plastic surgery, grafting, or amputation is required. The extent of penetration of the radiation is an important factor in the outcome of local injury. With heavy radioactive fallout, beta rays cause superficial skin burns, particularly on portions of the body not covered by clothing.

Whole-Body Exposure

Abnormalities in the most susceptible tissues are manifested in the first days and weeks after whole-body radiation exposure. A large, single exposure to penetrating radiation can result in various forms of the acute radiation syndrome (Table 3). Within the first 12 hours after exposure, there is a prodromal phase, consisting of nausea and vomiting, which lasts for up to 48 hours.

At doses exceeding 30 Gy of whole-body, penetrating radiation, cardiovascular and central nervous system damage occurs, primarily as a result of hypotension and cerebral edema. There is almost immediate nausea, vomiting, prostration, hypotension, ataxia, and convulsions. Death usually occurs within several days.

Acute, whole-body doses of approximately 10 to 30 Gy cause a gastrointestinal syndrome, primarily as a result of the death of intestinal mucosal stem cells. This syndrome is characterized by the rapid onset of nausea, vomiting, and diarrhea, which is followed by a latent period of approximately one week and then by recurrent gastrointestinal symptoms, sepsis, electrolyte imbalance, and ultimately death.

A clinically significant hematopoietic syndrome occurs after whole-body doses of 2 Gy or higher as a result of bone marrow depression. After the prodromal symptoms, there is a latent period of two to three weeks during which the patient may feel well. A reduction in the lymphocyte count can occur within 48 hours after exposure, and the magnitude of the reduction is a useful indicator of the radiation dose (Table 4). Maximal bone marrow depression with leukopenia and thrombocytopenia occurs several weeks after exposure, when hemorrhage and infection can be major problems. If the bone marrow is not completely eradicated, a recovery phase ensues, which may be enhanced through use of hematopoietic growth factors.If there is extensive skin injury, the damaged functions of the skin may interact with other organ damage. Some authors have referred to this as the "cutaneous syndrome."

A number of drugs that provide protection against radiation have been suggested for use in terrorist attacks. To be effective, most of these drugs need to be given before exposure. Amifostine is approved by the Food and Drug Administration (FDA) for some patients undergoing radiation therapy, but it has serious side effects, including hypotension, which severely limit its use in emergency personnel who must engage in physically demanding activities. Androstenediol has recently been proposed as a prophylactic drug, but it has been evaluated only in animals. Moreover, androstenediol boosts the immune system, which is required only if the radiation dose approaches the lethal level. Bone marrow transplantation, which has been performed in patients with whole-body doses in excess of 12 Gy, has not been helpful. Experience with accidental exposure has shown that, even if the hematopoietic syndrome is successfully treated, death invariably follows from radiation pneumonitis, denudation of the alimentary tract, and hepatic and renal dysfunction.

Internal Contamination

Internal contamination can occur from the dispersal of powdered, liquid, or gaseous radioactive material. The material may enter the body by inhalation or ingestion, through intact skin, or through wounds or burns. Effective treatment requires knowledge of both the radionuclide and the chemical form. Unless treatment is instituted quickly, its effectiveness will be limited. There are several general approaches to the treatment of internal contamination, including reduction of absorption, dilution, blockage, displacement by nonradioactive materials, mobilization as a means of elimination from tissue, and chelation (Table 5).

In the event of the detonation of a nuclear weapon or the release of radioactive material from a nuclear reactor, the most likely treatment of internal contamination would be the use of potassium iodide or iodate to prevent radioiodine from accumulating in the thyroid. The recommended daily dose of potassium iodide is 130 mg for adults, 65 mg for children 3 to 18 years old, 32 mg for children 1 month to up to 3 years old, and 16 mg for infants less than 1 month old. Potassium iodide must be taken shortly before exposure or within several hours after exposure to be effective. Both the Nuclear Regulatory Commission and the FDA have approved the use of potassium iodide in emergencies. Potassium iodide is widely available through the mail and the Internet. Too high a dose will result in iodism, but the risk of serious side effects with the recommended dose is extremely small. Chelating agents (calcium or zinc diethylenetriamine pentaacetic acid) are investigational drugs and are useful only if there is direct dispersal of plutonium or americium. Such agents are not very useful for the treatment of contamination with other radionuclides, and they are not useful after the detonation of a nuclear weapon.

External Contamination

Radioactive contamination of clothing and exposed skin does not constitute a medical emergency. Management of such cases of exposure is simply a matter of removing and controlling the spread of radioactive materials. Removal of clothing usually results in the elimination of 90 percent of the contamination. Even extensive surface contamination is not likely to result in overexposure on the part of medical personnel. When workers at Chernobyl who were in the reactor area at the time of the nuclear accident were decontaminated, the medical personnel at the site received less than 10 mGy of radiation. Medical personnel should wear protective clothing and gloves in conformity with universal precautions. Respirators are not required at the hospital but should be worn by rescue personnel entering highly contaminated areas.

If the patient has surface contamination and no physical injuries, decontamination can be effectively performed with the use of water and detergent. If there is substantial physical trauma, or if there are life-threatening injuries in addition to surface contamination, the patient should be stabilized physiologically before decontamination is performed. The skin is an important barrier and should not be abraded during decontamination. All contaminated materials should be placed in large, labeled plastic bags, with proper disposal of the bags.

Contaminated Burns and Wounds

If a patient with surface contamination has a wound that is not contaminated, it should be covered until the radioactive material has been removed. A wound that contains radioactivity should be rinsed with saline and treated according to conventional aseptic techniques. Excision is usually reserved for long-lived radionuclides (especially alpha-emitting radionuclides). If the patient has received a whole-body dose of radiation that exceeds 1 Gy, the wound should be closed as soon as possible so that it does not become a portal for lethal infection. Contaminated burns should be gently rinsed and then treated in the conventional manner. Radioactive material often comes off with the exudate or eschar.

General Management

Management of events involving the dispersal of radioactive materials can be divided into three phases: preparation, management during the crisis, and management of its consequences. The preparation phase includes emergency planning, clarification of command and control issues, specification of organizational responsibility, development of notification criteria and communications systems, assessment of the type and quantity of equipment required, and specification of levels of protective actions that will be taken under certain circumstances.At all levels, the involvement of health care facilities is crucial. Most metropolitan-area hospitals are still not adequately prepared.

Training can be divided into training for the public and training for those directly dealing with radiation or contamination. The specific components of training depend on the potential level of radiation exposure and on the task at hand. Training for emergency personnel should include information about the nature of radiation, levels of risk, methods of protection, and priorities for management. Training must also include mock exercises with an emphasis on large-scale disasters and terrorist events. In addition to training, there must be an assessment of the availability of beta–gamma survey instruments and dose-rate meters, potassium iodide, and reference materials. There should also be a program covering the measurement and recording of doses, use and maintenance of dosimeters, and use of exposure information.

In the event of a terrorist incident, the Federal Bureau of Investigation is the lead federal agency in the United States during crisis management in other countries, an appropriate resource should be identified. Crisis management refers to activities undertaken to ensure that there is no further threat and to establish control over the site of the attack as a crime scene. Consequence management refers to prevention or limitation of further damage, protection of the public, decontamination, and disposal of radioactive material. During consequence management, the Federal Emergency Management Agency becomes the lead federal agency in the United States.In both phases, a federal joint operating center is established to work with other federal agencies.

Intervention refers to actions taken to reduce the exposure to and dose of radiation. These actions may include controlling access to the site, directing people to stay indoors or evacuating them, removing contaminated clothing, providing respiratory protection, administering potassium iodide, restricting certain foods, and decontaminating property. Guidelines have been developed that specify which actions to take if a particular dose level is likely to be reached.

According to international recommendations, people should stay indoors for up to two days if a dose of 1 rem is likely to be reached, with evacuation for up to one week if the likely dose is 5 rem or higher. Temporary relocation is recommended at a likely dose of 3 rem in the first month or 1 rem in a subsequent month. Permanent resettlement is recommended if the lifetime dose is expected to be 100 rem. The administration of potassium iodide is recommended if the estimated dose to the thyroid is 100 mGy or higher. There are similar criteria for the restriction of food and milk if the activity of radionuclides exceeds a certain level. Experience with prior events has provided the basis for the establishment of exposure limits and levels of radioactivity in food and water that are thought to be safe. (Safe levels are usually defined as those associated with a risk of death of 10^–4 to 10^–6 annually.)

With regard to the actions of emergency personnel, the occupational dose limit (5 rem per year) does not apply.⁴³ According to the guidelines of the Environmental Protection Agency, the dose limit for persons providing emergency services other than lifesaving activities is 5 rem per event; for lifesaving activities, the dose can exceed 25 rem per event. The North Atlantic Treaty Organization uses 150 rem as the limit in a disaster. The cumulative dose is difficult to measure in emergency personnel, and dose-rate criteria are usually used. At a dose of 0.1 mGy per hour, emergency personnel may enter an area to perform critical, time-sensitive tasks.² At a dose of 0.1 Gy per hour, exposure may be life-threatening, and emergency personnel should return to their control point to await instructions from a radiation expert on how to proceed.

Early Management

Initial management consists of on-the-scene triage and transportation of victims to emergency rooms for treatment. The principles of handling hazardous materials, which are based on the assumption that the toxic environment is relatively contained, provide for maximal protection of a few workers while they are rescuing a small number of patients. This approach will not be practical if there are large numbers of casualties and little or no notice. Persons with life-threatening injuries should be handled as if they were contaminated and taken to a local hospital. Those who are uninjured or have minor injuries should be evacuated (upwind if possible) and then evaluated for possible contamination. The usual procedure for on-the-scene decontamination is not adequate if there are large numbers of patients. In the event of a chemical and biologic event, the local health care facility is primarily responsible for decontamination, but this approach is not necessary and may even be inadvisable in the case of widespread dispersal of radioactive materials.

Ambulance staff should wear gowns and gloves and appropriately dispose of the victims' outer clothing. The hospital should be informed of the imminent arrival of seriously injured and possibly contaminated patients. Contaminated persons who are uninjured or have only minor injuries should be taken to a designated center for registration, decontamination (removal of clothing and showering), and treatment of minor injuries. Persons who report nausea, vomiting, or diarrhea should be referred to a hospital for evaluation of whole-body exposure. If possible, the evaluation should be performed at a facility other than the one providing care for contaminated patients who have life-threatening traumatic injuries.

In the emergency room, patients should receive care in an area where access is controlled (with the use of ropes and signs), and exits should be monitored so that contamination is not spread. Security is necessary to prevent unauthorized access. The medical staff should adopt universal precautions. Patients can be moved with minimal spread of contamination by wrapping them in cloth sheets. Containment of wastewater is probably not possible, and its release can be justified in almost all situations.