Worldwide, there have been hundreds of recorded accidents with significant radioactive contamination, but only the accidents that occurred at Chernobyl, Ukraine, and Goiania, Brazil, resulted in significant numbers of children who required internal and external decontamination (go to: historical overview earlier in this chapter). Radionuclides are widely used in research, medicine, nuclear power, and industry, so further incidents of external and internal contamination will certainly occur. Exposure to radionuclides can occur in peacetime and as a result of a terrorist event such as use of a radiological dispersal device (RDD). Both military and civilian populations are potential targets.
Medical management requires knowledge of the physical and chemical characteristics of radionuclides, as well as the indications and methods for their removal from the body. Patient management must be a team effort that includes physicians, other health care professionals, and health physicists. Patients can be contaminated by any one of the hundreds of radioisotopes in common use, although only a limited number are medically significant. The medical effects from these different exposures vary. Reference materials, such as the National Council on Radiation Protection and Measurements (NCRP) Report No. 65, health physics texts, and standard operating procedures, can be used to guide patient management.
Internal contamination occurs when radioactive material enters the bodies of unprotected people through inhalation, ingestion, or wound contamination. Health physicists have defined internal contamination as "unwanted radioactive material present in the body." Contamination and exposure are not the same. Patients can have external exposure to radiation, external contamination by radioactive material, internal contamination with radionuclides, or any combination thereof (Figure 6.7).
ARS has occurred after contamination with high-energy isotopes (e.g., Cs-137). However, internal contamination is usually asymptomatic initially, with no acute medical effects. The main medical concerns are chronic radiation injury of target organs, such as lung or bone, and long-term stochastic effects, such as malignancy.
The greatest public concern currently centers around terrorism involving radioactive materials. However, medical errors made during medical diagnosis and treatment historically have been the most common cause of significant internal contamination. Industrial accidents are the second most common cause. Institutional and military use of a great number and variety of isotopes has also led to contamination events.
The most likely terrorist use of radioactive materials would be an RDD, variously referred to as a contaminated conventional explosive or "dirty bomb." Such a weapon can contain any liquid or particulate radioisotope. There is no nuclear detonation. Rather, the radioactive material is actually most hazardous before the explosion, when it is concentrated in one place. The goal of terrorists is to add a radionuclide to an existing bomb (e.g., truck bomb) to create an RDD that can contaminate both victims and the surrounding terrain.
First responders can take several steps to avoid injury from a suspected RDD explosion. RADIAC devices can be used to detect radioactivity at a distance, confirming the RDD. First responders should don protective gear before entering the site and setting up a safe perimeter. A health physicist or a nuclear-biological-chemical team can then analyze samples using specialized laboratory equipment to determine the specific radionuclide.
Internal contamination and casualties are most likely to occur from common radionuclides linked to improper disposal of radioactive sources or damage to a medical or commercial facility. Commonly used radioisotopes include high-energy gamma emitters, such as cesium (Cs)-137, cobalt (Co)-60, and iridium (Ir)-192. These materials are used in industrial and research applications, medical and commercial irradiation, tracer units, thickness gauges, and calibration devices. Standard nuclear fuels, such as uranium and plutonium (Pu) isotopes, are also relatively common. Radioactive iodines (e.g., I-131), Cs-137, and strontium (Sr)-90 are the most medically important fission products associated with rupture of a reactor core or radioactive fallout from nuclear weapon detonations.
Radionuclides, their non-radioactive (stable) counterparts, toxins, and chemicals are all governed by the same principles of toxicology. The same pharmacokinetics also apply, as all toxic agents must be absorbed, distributed, and expressed (through toxicological effects on target organs). Factors that determine the amount of internal hazard are the amount of radionuclide, the energy and type of radiation, the length of time in the body, the inherent chemical toxicity, and the critical organ(s) affected. The greatest potential for radiological injury is from large amounts of very energetic, long-lived radioisotopes that can affect certain critical (target) organs.
Biological half-time. Biological half-time (biological half-life) is defined as the time required for half of a substance to be removed from the body. This number comprises both the physical half-life and the metabolic clearance of a radioisotope. A treatment plan can be developed by combining information on half-life and the amount of nuclide exposure. This requires knowledge of the exposure and access to reference texts or experts, because every isotope and chemical formulation has a different half-time. For example, salts of Cs-137 have a half-time of 68-109 days, while tritium (H-3), Pu-239, and soluble uranium salts have biological half-times of 8-12 days, 100 years, and 15 days, respectively.
The critical organ. The critical organ is defined as the bodily location where an isotope exerts its primary effect. A radioisotope is chemically identical to a stable isotope of the same element. Both are metabolized according to their chemistry, so that the critical organ is determined by the chemical properties of the isotope.
Radionuclides that distribute to the whole-body include sodium (Na)-24, Cs-137 (which mimics potassium) and tritium (which is incorporated into water). Bone is the critical organ for radioactive minerals that the body uses as calcium. Similarly, radioactive iodides (e.g., I-131) are rapidly concentrated in the thyroid gland. Ultimately, these toxins will be eliminated through the body's normal excretory mechanisms.
The life cycle of a radioisotope consists of its several stages of transit through the body:
Radioactive materials can enter the body through inhalation, ingestion, and skin penetration.
Inhalation pathway. Inhalation is the most efficient route of absorption for most toxins, including radionuclides in insoluble particulate aerosols. Large particles are deposited only in the upper airways, from which the mucociliary system clears insoluble particles. The "respirable fraction" is 1-5 microns in size, which is the size associated with efficient deposition in the terminal bronchioles and alveoli. The most hazardous biowarfare agents (e.g., anthrax spores) and industrial dusts (e.g., silica) are in this size range.
Insoluble radioactive particles continue to irradiate surrounding tissues until cleared from the respiratory tract. Soluble isotopes are absorbed quickly and completely from the entire respiratory tract. Insoluble particles are cleared from the upper bronchi within 1 hour, before much injury occurs. The clearance time from the alveoli can be 100 to 1,500 days or more for some compounds. Radioisotopes deposited within alveoli are cleared to regional lymph nodes, where they may remain or be transported systemically. Alpha radiation is the most damaging to alveolar tissue, causing fibrosis and scarring to a spherical volume of tissue around the particle, in addition to any local inflammatory response to the foreign particles.
Ingestion pathway. Swallowed radioactive material enters the digestive tract and is handled like any other ingested material. This is true for material originating from contaminated food or water, as well as for material cleared from the respiratory tract. As with inhalation, absorption from the gastrointestinal (GI) tract depends on the isotope chemistry, including solubility. Most radionuclides are insoluble, with GI absorption <10%. These materials stay in the GI tract without becoming a systemic hazard. The clearance time for the GI lumen is 1-5 days. As a rule, insoluble alpha-particle emitters do not cause significant injury, because the exposure time within the critical organ is relatively short.
However, soluble radionuclides and strong gamma emitters—-which have occasionally been ingested—become a whole-body hazard and are capable of causing ARS. Soluble radionuclides are absorbed and metabolized according to their chemistry.
Skin pathway. Although intact skin is generally a barrier to most radionuclides, skin absorption can be important. Most skin absorption occurs through wounds or by passive diffusion. Examples of the latter include tritium-water and radioactive iodine, which can pass readily through skin. Skin permeability rates depend on relative solubility in both lipids and water. Infants are particularly at risk because of their thin epithelium and large surface area to mass ratio. Injuries such as trauma, burns, and chemical exposures also increase skin permeability. Abrasions and partial thickness burns create large denuded skin surfaces, which greatly increases absorption. Clinicians must evaluate all wounds for the presence of radioactivity, and thoroughly clean, debride, or excise all contaminants.
Uptake can occur by simple deposition, diffusion, or metabolic processes. Many soluble nuclides are metabolic analogs of body chemicals, so the body incorporates them like normal building blocks. The critical organs for these soluble nuclides are identical to storage sites for their metabolic analogs (e.g., radium, calcium, and bone). Once a soluble radionuclide is absorbed, it may distribute to the whole body. The liver, kidney, adipose tissue, and bone have higher capacities for binding chemicals, including radionuclides, due to their high protein and lipid content.
Insoluble radionuclides pass through the GI tract unchanged. At least some of the absorbed nuclide is eventually excreted, either in its original state or as metabolites. The main route of excretion is via urine, particularly for water-soluble compounds. Lipid-soluble compounds are excreted via the bile into the intestine. There is much individual variability in elimination.
Clinicians may need to evaluate patients who are both contaminated and injured. Furthermore, patients with internal contamination will almost certainly be externally contaminated at the time of exposure. Initial management and diagnosis should be performed simultaneously if possible. Any life- or limb-threatening medical or surgical emergencies should be addressed first. Initial emergency care is the same as for cases unrelated to radiation injury, because contamination causes no acute medical effects. Assessment and treatment of internal contamination must wait until the patient is medically stable and external decontamination has been completed.
The initial evaluation begins at the same time as emergency treatment and consists of the following:
History. Patients exposed to radiation are usually asymptomatic at the time of presentation. However, history is still the biggest component of initial diagnosis of contamination. Typically, the patient or someone else provides the important information that an exposure occurred. To quote the experts, "How does a physician become aware that his patient(s) may have an external exposure to radioactive material? Usually, someone tells her."
After a radiological attack, the history provides the best initial indicator of the likelihood of internal exposure. The history should include the exposure setting (e.g., enclosed space, open air in fallout field, etc.) and the protection status of the patient (e.g., wearing a mask). The patient or a fellow worker may know which isotope was used, or this may need to be determined by a health physicist in the laboratory.
Initial patient survey and nasal swabs. The initial external survey of the body can be performed using standard RADIACs with both beta-gamma and alpha probes. Nasal swabs collected before decontamination can help diagnose, but cannot exclude, a significant inhalation injury (because the nares are self-cleaning). These swabs should be collected early, in the first hour and before the patient is washed off or showered, but decontamination should not be delayed just to obtain nasal samples.
Each nostril should be swabbed separately, and the radioactivity on each swab measured using a RADIAC. The swabs should be saved. Activity measured by a RADIAC on a nasal swab reflects lung deposition. Health physicists can calculate the lung burden of the contaminant using standard equations and extrapolation curves. If both nostrils are "hot," the patient probably inhaled contamination. If only one nostril is hot, the patient either has touched his nose with a contaminated finger (suggesting no lung contamination), or there is unilateral nasal obstruction.
The laboratory tests most familiar to medical personnel (e.g., CBC and chemistry panels) are not helpful in diagnosing internal contamination. Instead, internal contamination is measured either directly with RADIACs or indirectly using samples of body fluids and excreta.
Direct measurement. Machines such as RADIACs and larger stationary units such as whole-body counters directly measure radioactivity of the body. The operator sweeps the RADIAC slowly over the body, maintaining a constant distance above the skin. A whole-body counter is a large fixed device, associated with a heavily shielded walk-in or lie-down chamber. This is the most reliable diagnostic instrument, although availability is limited.
Indirect measurement. Body fluids (obtained by swabs), tissue samples, and excreta can be directly examined for radioactivity and for the specific radioactive isotopes involved. A health physicist can then estimate the patient's "body burden" using extrapolation curves.
Nasal swabs should be obtained as soon as possible after contamination, as noted above. These are sent with the patient to the medical facility. Medical or health physics personnel should also take a wipe sample from the surface of wounds or skin wherever hot spots are noted via RADIAC.
The level of radioactivity in urine and feces can also be used to estimate internal contamination. Initial radioactivity in urine and feces should be quantified with a baseline sample, followed by multiple postexposure urine and fecal samples. A thorough evaluation of serial samples is the only sure method of confirming contamination and quantifying body burden, which are key components of successful treatment.
Bioassay methods vary according to each nuclide. Published methods can be found in health physics texts and standard guidance documents (e.g., NCRP Report No. 65). Table 6.7 summarizes the sampling regimens for some important radionuclides. Biodosimetric approaches are useful for insoluble nuclides that are either ingested or inhaled, because inhaled particles will be swallowed and passed through the GI tract into feces.
Tritium exposure can be measured with a single voided urine sample. For uranium, a baseline 24-hour urine sample should be collected as soon as possible after the exposure. This establishes the pre-existing excretion of uranium commonly distributed in soil. This initial urine sample is then followed by another 24-hour sample to measure new contamination and an additional 24-hour sample 7-10 days later. Insoluble plutonium may not appear in the urine until 2-3 weeks after ingestion, so both urine and fecal bioassays are needed to identify this radionuclide.
Various instruments are available for detecting and measuring radiation, which cannot be detected by human senses. These instruments (Figure 6.8) use the energy of the radiation to create an electrical "pulse," which can then be measured and used to determine information about the radiation field. These various Radioactivity, Detection, Indication, and Computation meters are generally referred to by the acronym RADIAC.
Radiation detectors can be configured in several different ways. Some have an internal probe, while others have an external probe connected by a wire. The intended use of the meter is the most important factor in determining what configuration to use. If the meter will be used only for large area surveys, an internal probe works fine. If the meter will be used to determine the dose rate from a point source or to detect contamination, then an external probe will most likely be used.
Things to check before using a RADIAC:
There are two main classes of RADIAC instruments used to detect and survey for ionizing radiation: gas-filled and scintillation detectors.
The first and oldest type of RADIAC is the gas-filled detector. These are constructed by filling an electrically conductive chamber with an inert gas. The system contains two electrodes, one through the center of the chamber and the chamber itself, which also functions as an electrode. When a voltage is applied to the system, the center wire becomes positively charged (anode) and the outer (chamber) electrode takes on a negative charge (cathode). The fill gas, usually a noble gas such as argon, helium, or neon, is ionized by the radiation that strikes and penetrates into the chamber. This produces a pair of ions (a positive base ion and a free electron), which are attracted to the electrode of the opposite charge. The free electrons that are collected along the anode then create an electrical impulse. The electrical impulse (or current) is measured and converted to a meter reading, generally in counts/min or mR/hour.
As the amount of voltage applied to the tube increases, the attractive forces of the anode and cathode get stronger and the production of secondary ionizations increases. Secondary ionizations are those not caused by the incident radiation, but by multiplication within the inert gas (gas amplification). There are six distinct regions corresponding to the amount of voltage applied.
Detectors are described according to the radiation regions they detect. The regions most commonly used for detection are the Ion Chamber Region, the Proportional Region, and the Geiger-Mueller Region.
The other common type of detector is the scintillation detector, which uses a liquid or a solid phosphor crystal. When radiation strikes the crystal, the energy of the incident radiation is expended to produce ionization and excitation. The ion that was formed eventually recombines, or the excitation decays, both of which result in the production of light. On average, the number of light photons emitted is proportional to the amount of energy originally deposited. A photomultiplier tube is then used to convert the scintillation photons (light) into an electrical pulse, which is counted or otherwise analyzed electronically. Some common scintillators use zinc sulfate, sodium iodide, or plastics. To detect alpha particles, scintillation detectors must be held 1/16th-1/8th of an inch from the surface being monitored because of the short range of alpha radiation.
The so-called multi-function RADIACs represent a modern innovation in radiation monitoring. These instruments use one readout unit, which can be connected to various probes so that most types of radiation and contamination can be detected. Most of these units use what is called a "smart box," which can detect the type of probe being used. These "smart" units automatically show the correct units for the monitor being used and calibrate themselves accordingly. Many of these units come with everything in one case, eliminating the need to carry many separate detectors.
Dosimeters are a special type of instrument used to determine the total dose of radiation that a person receives. The simplest dosimeters are made of film (like camera or x-ray film), tiny wafers of plastic, or other specially formulated materials that respond to radiation in ways that can be assessed and matched to a particular radiation dose. Simple dosimeters require special processing to determine dose but are very reliable and accurate.
Slightly more complex are pocket ion chambers, which use the ionization caused by radiation to move a very tiny fiber that tracks the dose. Pocket chambers are inexpensive and can be read directly, but they are not very accurate and have to be protected from bumps that might cause the needle to move.
The standard dosimeter for most radiation workers, including medical personnel, is some form of thermoluminescent device (TLD). These use some type of crystal, such as lithium fluoride (LiF), calcium sulfate (CaSO4), or calcium fluoride (CaF) as the detector element. These dosimeters are usually read by placing them in a machine that heats the crystal and reads its light output, which is proportional to the radiation dose received. An advantage of some TLDs is that one dosimeter can be used for beta, gamma, x-ray, and neutron radiation. Another advantage of the LiF dosimeters is that they are relatively resistant to "fade" (i.e., the loss of dose over time) and are sensitive down to 1 mrem (new LiF-Cu version).
Finally, electronic dosimeters have become popular. Most are about the size of a personal pager. These are more costly than pocket chambers but are much more reliable, accurate, and rugged. They also have a variety of features (e.g., alarms, digital readouts, dose rate readout, etc.) that can make them attractive to many first responders.
This discussion describes many aspects of personal protective equipment (PPE), including the following:
Radioactive isotopes in the form of dust particles can harm a victim via external or internal contamination. Radioactive contamination can be carried by air currents in the form of fallout, which may travel great distances or settle on surfaces locally, depending on climactic conditions. In war-torn countries, children can potentially be contaminated externally by radioactive particles on the skin or clothing or by playing on vehicles that have been destroyed by depleted uranium munitions. Terrorist attacks with RDD (dirty bombs) can also generate considerable risk of contamination. PPE can protect a health care provider from contamination when dealing with casualties from such events.
In internal contamination, radioactive material enters the body via inhalation, ingestion, or wound penetration. A small amount of radioactive material could also enter the body through the mucus membranes of the eyes.
Personal protective equipment refers to three types of equipment:
The goal of PPE is to prevent an individual from becoming contaminated and to prevent the spread of contamination from an already contaminated person. PPE does not shield the wearer from penetrating radiation, such as photons.
First responders. PPE should provide protection to the skin, respiratory and digestive orifices, and the eyes. Boots are part of the PPE needed to prevent contamination of footwear with radioactive material. The PPE should be sturdy enough to avoid tearing in emergency situations. If the PPE is not airtight, tape may be placed where the PPE suit contacts gloves and boots to avoid radioactive material from getting inside the suit. A variety of PPE is available commercially. The National Institute for Occupational Safety and Health (NIOSH) provides information and a statement of certification for respirators at http://www.cdc.gov/niosh/npptl/.
Hospital personnel. Radioactive fallout in the air should not be present inside a medical facility. Therefore, medical personnel working inside a facility do not need to wear as much PPE as first responders. Medical personnel who are decontaminating patients or providing emergency care to patients who have not yet been decontaminated should wear PPE similar to that worn in the operating room (e.g., head cover, face mask, scrubs or gown, and shoe covers). Wearing double gloves is recommended, in case the outer glove tears or breaks.
First responders should wear PPE appropriate for "all hazards," because the type of hazard may not be initially known. However, radioactive material is easier to identify than chemical or biological material, because it can be readily identified with a RADIAC. If the hazard is identified as solely radiological, then first responders can reduce their level of protection to that necessary for radioactive material (e.g., self-contained breathing apparatus is not usually needed). Waterproof PPE is appropriate if the contaminant is wet. Otherwise, cotton or Tyvek® coveralls would be adequate.
A person without PPE in a radioactive environment should take immediate emergency precautions, including the following:
Adults should direct children to do the same and lead the children to a safe area.
PPE may have radioactive contamination after an event. All such PPE should be collected in one area, placed in plastic bags (preferably red or yellow), and labeled as radioactive material. A health physicist can later evaluate the material for the presence and amount of radioactivity and then advise if the PPE can be washed without radiation precautions, should be disposed of, or should be stored in a special manner.
The Department of Energy (DOE) Web site "Radiation Emergency Assistance Center/Training Site (REAC/TS)" at http://orise.orau.gov/reacts/rad-incident-response.htm provides guidance on proper use and disposal of PPE. Key information is summarized below.
The DOE Web site "Radiation Emergency Assistance Center/Training Site (REAC/TS)" at http://orise.orau.gov/reacts/rad-incident-response.htm also presents guidance on recommended procedures for monitoring of personnel (Figure 6.9).
The various aspects of decontamination include the following:
The primary objective of skin decontamination is to prevent internal contamination through secondary ingestion or inhalation. The secondary objective is to minimize the radiation dose to the skin. Each potentially exposed person should be monitored. Contamination levels should be recorded in the appropriate location on a form containing an anatomical figure.
Decontamination priorities are as follows:
Simply removing clothing may eliminate up to 95% of contamination.
Treatment of life-threatening injuries always takes precedence over decontamination. No U.S. health care worker has ever suffered a radiation injury from caring for a contaminated patient.
An individual is generally considered "clean" if all areas of the body are below 100 counts/minute above background.
For a conscious patient, the first step is an interview. Ask for a description of the contamination event (to determine likelihood of internal contamination), extent of skin contamination, and number of other people affected. The next step is decontamination of eyes, ears, nose, skin, and injury site, which should be performed (or supervised) by medical personnel familiar with decontaminating these body areas.
A number of techniques have proved quite effective for decontamination of radioactive material. The least invasive, or least potentially damaging, technique should be done first before moving to more aggressive techniques. The need for decontamination must be balanced with potential injury to the skin caused by aggressive decontamination methods. The individual should be monitored after each decontamination attempt.
For a dry particulate or dust, the "tape-press method" has proven to be effective. In this procedure, an adhesive tape (e.g., masking tape) is pressed onto the contaminated area to lift off the contaminant. Strongly adhesive tape (e.g., duct tape) should not be used, because it may damage skin. The tape-press method should not be used on hairy areas or fragile tissue, such as eyelids.
Washing a contaminated area with soap and water for 1-3 minutes is very effective. The goal of this type of decontamination is to float the contaminants off the skin and rinse them away. This can be done in a basin for small areas of contamination, or in the shower if large portions of the body are contaminated. If plain soap and water are ineffective, then a mild abrasive soap (such as Lava® or Soft Scrub®) may be used. If only a small area of skin is contaminated, waterless hand cleaner may be used instead of soap and water.
During washing, care must be exercised not to splash contaminated wash solution around the area. A washcloth or soft surgical scrub brush may be used to help remove contamination. The water should be lukewarm, and care must be taken not to damage the skin. If erythema becomes evident, decontamination should be stopped to prevent driving contaminants into the skin.
If washing is not effective, the site should be wrapped or covered with a bandage to allow removal through sweating and skin sloughing. Both the contamination site and the bandaging material should be monitored after 6-9 hours to determine effectiveness of this technique.
Irrigation with sterile water or saline has proven to be effective for wound decontamination. If the wound is a mild burn or abrasion, gentle washing with soap and water may be effective. All contamination does not have to be removed, because the residual remaining on the surface will normally be incorporated into, and sloughed off with, the scab. For contamination remaining in a puncture wound, simple wet debridement may be used following standard surgical procedures. However, before any surgical procedure, careful consideration should be given to the risks/benefits of the procedure.