Public Health Emergency Preparedness
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Chapter 6. Radiological and Nuclear Terrorism (continued)
Radiation Biology and Dosimetry
Ionizing radiation interacts with biological systems through discrete energy deposition events referred to as spurs, blobs, and tracks. This can occur by direct interaction with cellular and tissue component targets or through the indirect production of free radicals (e.g., hydroxyl radicals, etc.) or other harmful molecules. Radiation-induced damage to DNA and the cellular capacity to repair DNA/chromosome damage have a major influence on the deleterious cellular effects. Additional cellular-specific parameters (e.g., oxygen tension, cell-cycle distribution, proliferative status or rate of cell division, extent of cell differentiation, etc.) and radiation-specific parameters (dose, type of radiation, dose rate, etc.) can modulate the degree of cellular and tissue injury.
The consequences of radiation exposure to cells and tissues are highly variable, including both acute effects (e.g., delay in cell division, cell death) and late effects (e.g., cataracts, mutagenesis, carcinogenesis, etc.). Tissues vary in sensitivity to radiation; various tissues in order of most to least sensitive are lymphoid, gastrointestinal, reproductive, dermal, bone marrow, and nervous system. The response to radiation of self-renewing tissues is dynamic and influenced by tissue-specific transit times. Transit time includes both the time course for stem-cell differentiation and for the lifespan of mature, functioning cells.
Effective medical management for suspected radiation overexposure necessitates the recording of dynamic medical data and the measurement of level of injury using appropriate radiation bioassays. Biodosimetric assays can provide diagnostic information to the attending physician, as well as an estimate of the dose for personnel radiation protection records. Radiation biodosimetry usually encompasses multiple parameters, including the following:
- Radioactivity measurements and monitoring of the exposed individual.
- Observation and recording of prodromal signs/symptoms and erythema.
- Complete blood counts with WBC differential.
- Chromosome-aberration cytogenetic bioassay, using the "gold standard" dicentric assay for dose assessment.
- Bioassay sampling (if appropriate) to determine radioactivity contamination.
- Other available approaches.
The biological response to an absorbed dose of ionizing radiation should be assessed to predict the medical consequences. Physical dosimeters (e.g., film badges) may misrepresent the actual radiation dose and may not be available in a radiological accident or terrorism incident. Multiparameter dose assessments represent the current approach on which to base medical treatment and management decisions. Radiation syndromes are generally characterized into three phases: prodromal, manifest, and latent. The early or prodromal signs and symptoms will be emphasized later in this chapter.
Radiation-induced signs, symptoms, and erythema should be recorded during the course of medical management for radiation casualties to help triage patients and to guide medical management of casualties. Default standard mechanisms and procedures include recording of medical data by the respective medical responders and health care providers.
Additional medical guidance available to first responders and health care providers includes the following:
- International Atomic Energy Agency's (IAEA) Generic Procedures for Medical Response during Nuclear and Radiological Emergency (http://www-pub.iaea.org/MTCD/publications/PDF/EPR-MEDICAL-2005_web.pdf).
- Armed Forces Radiobiology Research Institute's (AFRRI) radiation casualty management software application (i.e., Biodosimetry Assessment Tool or BAT), which was developed for radiation casualty management. It is distributed to authorized users who have access to the AFRRI Web site.
The BAT software application equips health care providers with diagnostic information (e.g., clinical signs and symptoms, physical dosimetry, etc.) relevant to the management of radiation casualties. Designed primarily for prompt use after a radiation incident, the program facilitates the collection, integration, and archiving of data obtained from exposed individuals. Data collected in templates are compared with established radiation dose responses obtained from the literature to provide multiparameter dose assessments. An integrated, interactive human body map permits convenient documentation of the location of a personnel dosimeter (if worn by the individual at the time of exposure), radiation-induced erythema, and radioactivity detected by an appropriate radiation detection device.
Radioactivity Counting and Bioassay
In the case of suspected internal radioactive contamination, the following processes are typically performed concurrently:
- Decontamination to minimize the local radiation dose to the potential wound site.
- Removal and collection of metallic (or other) fragments for isotope identification.
- Biological sample collection for determination of committed dose.
Monitoring/sampling of wounds (i.e., wound swabs or wound cleansing wipes), body orifices (i.e., nasal swabs, oral swabs), and skin surfaces (i.e., wipes) should be performed for confirmation of internal contamination. Although not strictly considered biological samples, metal fragments, bandages/dressings, and clothing should be retained for isotope identification.
Biological specimens should also be collected to determine possible internal radionuclide deposition. Urinalysis and fecal sample analysis are the primary in vitro methods for determining internal dose. Urine is generally a high priority for bioassay, and therefore, "spot" urine as well as 24-hour urine specimens should be collected from accident victims.
In the special case of an improvised nuclear device or any event involving nuclear fission, there is also a need to collect whole blood specimens for biodosimetry. The blood specimens should be labeled, packaged, and shipped to the network of radionuclide bioassay laboratories for neutron activation analysis to estimate individual neutron doses for the casualties.
Prodromal Signs, Symptoms, and Erythema
The pattern of biological responses associated with acute radiation sickness (ARS) can provide initial diagnostic indices and help with triage of potentially exposed individuals. The early clinical responses associated with the radiation prodromal phase include the following:
- Abdominal pain.
- Parotid pain.
For the dose-dependent signs and symptoms associated with the prodromal phase of whole-body exposure to photon-equivalent radiation, go to Table 6.2. An increase in the exposure dose is associated with a parallel increase in both the constellation of prodromal signs and symptoms and the percentage of exposed individuals affected. For example, only 50% of individuals exposed to 2-Gy acute photon radiation will exhibit emesis. Radiation doses above 2 Gy will result in a progressive increase in the percentage of individuals who vomit and also express the broad range of prodromal symptoms.
Radiation exposure produces a predictable pattern of changes in blood-forming tissues. A crude estimate of absorbed dose can be obtained by serial measurement of peripheral lymphocyte blood counts. Therefore, a complete blood count (CBC) with white blood cell (WBC) differential should be obtained immediately after exposure, three times a day for the next 2-3 days, and then twice a day for the next 3-6 days. Lymphocyte cell counts and lymphocyte depletion kinetics can be used to estimate exposures between 1 and 10 Gy photon equivalent dose range. This biodosimeter is useful only for a few days (<10) after exposure because of the transient nature of radiation-induced lymphocyte depletion.
The analysis of chromosomal aberrations, particularly the incidence of chromosomes with two centromeres (dicentrics) in peripheral blood lymphocyte cultures, is widely used to assess dose after exposure to radiation. Human T lymphocytes have a long half-life, and a small proportion survive for decades. The frequency of dicentrics after exposure to radiation remains fairly stable for up to a few weeks. After acute partial-body exposure, the irradiated lymphocytes rapidly mix with unirradiated blood, reaching equilibrium within 24 hours.
Blood for cytogenetic bioassay should generally be collected within 24 hours of the irradiation incident. Peripheral blood (10 mL) from the exposed person is collected in a lithium-heparin collection tube, although an EDTA tube can be substituted if necessary. The blood must be transported immediately to a cytogenetic laboratory that is familiar with biodosimetry according to internationally accepted guidelines. During transport, the sample should be chilled with cold packs sufficient to keep the sample cool (4°C) but not frozen. The blood lymphocytes are then isolated and stimulated to grow in culture. Cell proliferation is arrested in the first metaphase, and metaphase spreads are observed under a microscope. The observed level of dicentrics can then be used to estimate dose by comparison with an established dose-response curve.
High-dose partial-body radiation exposures represent a common clinical scenario after accidents. Differences of 10% in absorbed dose can produce clearly observable variations in biological response. Hematological recovery in heavily irradiated areas of the body will be possible if a sufficient number of stem cells survive in unirradiated or mildly irradiated portions of the hematopoietic system. Knowledge of the heterogeneity of the absorbed dose is particularly important in making appropriate medical treatment decisions for patients exhibiting radiation-induced bone marrow syndrome. Cytokine therapy will stimulate proliferation of spared stem cells, but in cases of whole-body stem-cell sterility, bone-marrow transplant or alternative therapeutic measures may become necessary. In high-dose partial-body exposure scenarios, chromosome damage measured in peripheral blood lymphocytes helps determine the absorbed dose.
Biodosimetry and Radiological Terrorism
Effective medical management of radiation casualties after a terrorist incident requires a coordinated and adequate biodosimetric assessment for individuals suspected of exposure. A Medical Field Card (Figure 6.3) should be kept with the patient and used to record early signs and symptoms. This is consistent with an all-hazard approach for medical first responders and health care providers. Emphasis should be placed on recording the characteristic early signs and symptoms of radiation exposure (Table 6.3). Table 6.2 illustrates several of the quantitative multiparameter biodosimetry indices (stratified by 100 cGy dose windows from 1 to 10 Gy) that could be used for early diagnosis and triage of suspect radiation casualties.
There are two important issues to consider when collecting appropriate specimens for radioactivity counting and bioassay in a mass casualty situation.
- A vigorous screening process should be implemented at an assessment center(s). This helps determine the most likely candidates for bioassay of internal contamination by external counting, using hand-held or portal radiation detectors. Effective screening assures that appropriate victims are assayed, while avoiding the default decision of assaying everyone. The latter could overwhelm the limited resources available for performing the analyses.
- Specimens must be shipped to confirmed qualified laboratories. It is imperative to have established laboratory standards for bioassay procedures for assessment of internal radionuclide deposition, as well as a robust certification process for the laboratory network that will be conducting the analyses. The Department of Energy (DOE) performs bioassay and dosimetry at a number of sites and also has a program (DOE Laboratory Accreditation Program) to certify these laboratories.
The above laboratories will probably be different from those providing blood cell counts and cytogenetic biodosimetry. During the first 3 days of a mass radiological casualty situation, each potentially exposed person should have a minimum of five CBCs with WBC differentials. To adequately address this requirement, additional assistance (i.e., deployable hematology laboratory capacity) will likely be required to supplement local medical resources.
Cytogenetic confirmation (lymphocyte dicentric assay) of clinical triage has been proposed to help deal with mass radiological casualties or when there is an urgent need for rapid results. Confirmation of clinical triage can generally be accomplished using a simplified assay that scores only 20-50 metaphase spreads per subject, as compared with a typical analysis of 500-1,000 spreads. However, additional scoring is recommended after the initial results are communicated to the physician to resolve potential conflicts in dose assessment and to assist physicians considering marrow-stem-cell transfusions to mitigate bone marrow ablation caused by high doses.
Compared with adults, children have a significantly higher risk of developing cancer from radiation exposure. For this reason, pediatricians should be prepared for any special medical needs supporting biodosimetry assessments. There is limited knowledge in the available literature about biological dosimetry in pediatric populations. Current models to determine committed dose based on internal contamination are generally based on adult population parameters. However, the procedures applied to the general population are probably applicable to children in most cases. Special containers are required for collecting radioactivity counting and bioassay samples from infants and children (e.g., pediatric urine collection device).
With today's microtechnology, as little as 1 mL of blood can be collected for blood cell counts and cytogenetic biodosimetry in children, given their smaller blood volume and concerns about blood loss. The kinetic lymphocyte depletion method is preferred over single blood lymphocyte counts of dose assessment, given that normal lymphocyte counts in children decrease with advancing age.
The cytogenetic bioassay (dicentrics in metaphase spreads) can also be used in pediatric populations, although normal values may need to be adjusted. The consensus background frequency of dicentrics is 1 in 1000 metaphase spreads for the healthy adult population. Children generally show a lower frequency of dicentrics, and older adults (older than 60 years) a slightly higher frequency, compared with the normal adult background. There is one report in the literature that children younger than 1 year of age may be relatively more radiosensitive. This study found that dicentric yields after in vitro irradiation of blood from children are higher than in blood from adults exposed to similar radiation levels.
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Medical Diagnosis: Acute Radiation Syndrome
Acute radiation syndrome (ARS) can occur from radiation exposures during peacetime or as a result of war or terrorism. A case of ARS can be caused by an accident with a military or civilian radioactive source or as a complication of medical treatment. A radiation dispersal device (RDD) would probably not result in exposures high enough to cause ARS, although it is possible. This section describes ARS as it has occurred since the 1940s and as it may occur in the future.
Acute radiation syndrome is also termed acute radiation sickness or radiation toxicity. It is an acute illness that presents as a combination of clinical signs and symptoms. These generally occur in stages during the hours to weeks after acute exposure to a high dose of penetrating radiation (e.g., >0.7 Gy). This syndrome generally occurs after irradiation of the whole body (or most of the body), although the signs and symptoms evolve as injury to various tissues and organs is expressed. ARS follows a predictable course after a high or potentially fatal dose of penetrating radiation (e.g., gamma, neutron, or high energy x-rays). ARS is usually associated with prompt exposure or exposure within minutes at a high dose rate, although fractionated doses can also induce ARS.
High doses of ionizing radiation cause depletion of stem cell lines and microvascular injury, which lead to the clinical features of ARS. The most radiosensitive cells are primitive/progenitor cells and other rapidly dividing cells, while slower growing and more mature cells are generally radio-resistant. The most radiosensitive mammalian cells, in decreasing order, include the following:
- Lymphocytes and oocytes.
- Other hematopoietic tissue.
- Small-intestine crypt cells.
- Hair follicles.
All of these cells contain rapidly dividing cell lines. Clinicians are familiar with the effects of radiotherapy and chemotherapy on these tissues, as sterility, bone marrow damage, diarrhea, and hair loss all involve radiosensitive stem cell lines. With survivable radiation doses, some stem cells survive, and their cell lines regenerate. Microvascular injury can result in dramatic systemic symptoms and in permanent and irreversible damage such as local radiation injury.
Clinically detectable effects first appear at doses >0.2 Gy (>20 cGy or 20 rad). These effects include decreased sperm count, chromosome abnormalities, and mild bone marrow depression. Whole-body radiation doses >0.7 Gy can cause clinical illness. The lethal dose 50 (LD50) for penetrating radiation is approximately 3.5 Gy for untreated patients and 5 Gy for those receiving full medical treatment. The LD50 is the dose of radiation that will kill half the exposed population.
All health effects from radiation exposure tend to follow a similar clinical pattern that can be divided into a series of time-dependent stages: prodrome, latent period, and manifest illness. At higher radiation doses, these stages are associated with shorter time of onset, more severe signs and symptoms, and decreased survival. However, there is individual variation, and symptoms may not occur in all patients.
The initial stage of prodromal symptoms (prodrome) begins within the first few hours to 2 days after exposure. Symptoms include nausea and vomiting, with subsequent malaise, fatigue, and weakness. This is a nonspecific clinical response to acute radiation exposure caused by the cell membrane and free-radical effects of radiation energy, as mediator chemicals such as histamine, interleukins, and cytokines are released.
On recovery from the prodrome, there is usually a latent period during which most symptoms subside, although fatigue and weakness may remain.
This is the full disease picture that develops from the clinical signs and symptoms associated with damage to major organ systems (e.g., blood-forming elements, intestine, cardiovascular, central nervous system [CNS]). The molecular cause of disease is DNA damage. Death is usually caused by sepsis.
ARS is not a single syndrome but rather a series of sub-syndromes, each of which evolves over time. The first syndrome involves the hematopoietic system, usually from doses as low as 0.7 Gy. The gastrointestinal (GI) system is affected next, followed by the cardiovascular system and the CNS. These sub-syndromes are progressive and additive with increasing dose, as each organ system is damaged in turn. The cardiovascular and CNS sub-syndromes are usually discussed together because both are rapidly lethal, caused by microvascular injury, and without effective treatment.
The hematopoietic system is affected at doses >0.7 Gy. Although the dose range has been stated as 1-5 Gy, the hematopoietic system actually begins to show damage at doses below 1 Gy, and damage continues at all higher doses. The stem cells of all bone marrow cell lines are affected, so that all production of all blood cells is reduced or stopped. The clinical severity increases with dose, with ancytopenia occurring above about 2 Gy.
The prodrome begins 3-26 hours after doses of 1 to 5 Gy, lasting 48 hours or less. The latent period is mostly asymptomatic, except for possible mild weakness, fatigue, and anorexia that lasts 3-4 weeks. Hair loss (which requires about 3 Gy) and weight loss appear at about day 14. The manifest illness phase sets in at 3-5 weeks, sooner at higher doses. Bone marrow atrophy with pancytopenia (Figure 6.4) can lead to hemorrhage and infection, similar to that which occurs in chemotherapy patients.
Uncomplicated cases can survive with treatment, which includes bone marrow resuscitation and prevention of infections and hemorrhage. Marrow irradiated to 3 Gy shows depletion of cells, which are replaced with fat. Many remaining cells undergo pyknotic death or look grossly abnormal, containing large, bizarre nuclei.
Typical changes in the peripheral blood profile occurs as early as 24 hours after irradiation. Figure 6.5 shows the pattern of blood counts over time after 3 Gy of exposure. Lymphocyte levels fall immediately on day 1. At about 4 weeks, cell counts are at their lowest. The depleted white cells and platelets predispose to hemorrhage and overwhelming infection. Treatment is aimed at protecting patients from infection and restoring blood-forming elements.
This sub-syndrome is also termed radiation enteropathy and is seen occasionally in the setting of radiation oncology or among victims of a high-dose regional abdominal exposure. Major injury of the GI tract is clinically evident at absorbed, whole-body doses of >5 Gy. The prognosis is grave at doses >6 Gy. Doses >8 Gy are generally lethal.
The prodrome begins abruptly in 1-4 hours (usually 1-2 hours), can last >48 hours, and can be severe. The latent period is 5-7 days, with symptoms of malaise and weakness severe enough to be disabling. The clinical course can be stormy during the manifest illness phase, with complete paralytic ileus as the mucosa breaks down. This is marked by abdominal distention, vomiting, diarrhea, and GI collapse. The damaged mucosa permits bacterial translocation and sepsis, which is the usual cause of death. If patients survive long enough, hematopoietic syndrome will develop concurrently.
Cardiovascular and CNS Sub-syndromes
The radiation dose affecting the cardiovascular system and the CNS begins at >20 Gy, with the full syndrome occurring above 50 Gy. Such extremely high doses have been rare, such as during nuclear fuel handling accidents, in which victims were near a critical mass that suddenly formed ("criticality event"). The key pathological insult is acute microvascular injury with increased endothelial membrane permeability, especially in the brain, leading to cerebral edema and its subsequent clinical effects. The prodrome begins in as little as 5-10 minutes, with rapid onset of uncontrollable nausea, explosive vomiting and diarrhea, and CNS signs that include epileptic seizures and altered mental status. The brief latent period lasts several hours to 2 days. During the latent period, victims have generally been lucid, even euphoric, with a clear sensorium. However, orthostatic hypotension and weakness are often present. The manifest illness phase is marked by rapidly deteriorating CNS status and reduced consciousness, with or without epileptic seizures and a measurable increase in intracranial pressure. Watery diarrhea, respiratory distress, and uncontrollable swings in systemic blood pressure are also common during manifest illness. Coma and death from cerebral edema occur in 2-3 days.
Other radiation-induced clinical sub-syndromes can be observed in special cases or severe exposures. These include radiation pneumonitis, as well as cutaneous and local injuries. Pulmonary effects often play a major role in patients who sustain lethal-dose exposures of >5 Gy, then survive for several weeks with hematopoietic and GI sub-syndromes. With high radiation skin doses, there is acute skin injury, often termed a radiation burn. This is the result of high doses limited to the skin, usually from poorly penetrating radiation (e.g., beta particles) or whole-body irradiation doses >6 Gy. Radiation burns are also a common complication of radiation therapy. Acute local injury can result from external radiation exposures in which parts of the body are shielded. For example, local injury can occur after exposure to a collimated radiation beam or to a highly radioactive material (e.g., radiotherapy or industrial source) placed in close proximity to tissue.
In an ARS patient, life-threatening medical complications should be addressed first (as in any life-threatening emergency). The other aspects of ARS can be treated after the patient has been stabilized. Airway/breathing/circulation (ABCs) of BLS, ACLS, should be addressed, along with other required emergency resuscitation. After the patient has been stabilized, the need for external decontamination can be addressed.
The first diagnostic step is to assess the dose of radiation exposure, which may not be obvious. A dose assessment involves collection and analysis of the medical data discussed in this section, as well as consultation with health physicists and subject matter experts. Clinicians and health physicists calculate or determine an initial estimate of dose, which is revised over time as more clinical and dosimetric data become available (Table 6.4).
The initial diagnosis provides an initial determination of dose that guides early treatment. Diagnostic steps can begin in an emergency department, in any acute-care setting, or even at a field hospital. The best and quickest diagnostic indicators are:
- The time to onset of vomiting (prodrome).
- The speed of lymphocyte depletion (serial lymphocyte counts).
The time to onset of vomiting provides an estimate of the prodrome and suggests a dose range. The clinician should then observe the onset and duration of the subsequent latency. These various times combine to provide an estimate of dose, which suggests a treatment plan (Table 6.5). For example, prodromal symptoms of vomiting that began 1-2 hours after exposure, with duration of approximately 24 hours, suggests radiation exposure in the range of 3-5 Gy (Table 6.6).
The most useful early laboratory test is the CBC, including an absolute WBC count. WBC counts should be performed every 6-8 hours during the first day after exposure and at least daily thereafter for the next week. Lymphocyte counts are the best rapid gauge of dose. The classic Andrews diagram for lymphocyte depletion curves (Figure 6.6) was published in 1965 and is still useful. Lymphocyte counts drop quickly with high radiation doses. A drop of 50% or more in 24 hours indicates a severe radiation injury.
Later Diagnostic Data
Later diagnostic data help to refine both the estimate of dose and the treatment plan. Data that should be gathered over time include physical dosimetry, biodosimetry, and clinical physical findings. These data should be recorded for all patients, regardless of symptoms or estimated level of exposure. Such group data may be crucial to clinical evaluation of individuals within the group. These data can also provide a pattern of illness for the group, which can lead to changes in the estimate of dose or even the diagnosis.
Physical dosimetry. The dose assessment method most familiar to medical personnel is physical dosimetry. This can be used for victims who wore a personal dosimeter (e.g., a film badge), thermoluminescent device (TLD), or pocket ionization chamber. However, it is unlikely that civilians—or even most police, firefighters, and military personnel—will have worn dosimeters. It is also important to remember that dosimeters can be damaged during the radiation event, rendering them unreliable. Therefore, clinicians should request dosimetric data from emergency response agencies or military units with trained technicians. Such specialized personnel may be able to estimate dose using radiation detection, indication and computation (RADIAC) equipment and isotope counters.
Biodosimetry. Biodosimetry can provide a good estimate of dose but requires specialized testing. This is performed at a few national centers, including AFRRI in Bethesda, MD, and the Radiation Emergency Action Center Training Site (REAC-TS) in Oak Ridge, TN.
To assess radiation dose, a researcher counts the radiation-induced chromosomal abnormalities in peripheral blood lymphocytes. The classic method is a standard genetic karyotype, which takes about 3 days but offers a good dose estimate. This approach counts the aberrations on a chromosome smear, especially aberrations involving two or more centromeres (dicentrics). The number of chromosomal abnormalities correlates directly with radiation dose (Appendix E of the AFRRI Handbook, available at http://www.afrri.usuhs.mil).
Radiation-induced skin injury. Skin changes after radiation exposure offer a rough estimate of minimum dose, given that skin changes do not develop below about 3 Gy. Radiation-induced skin injury takes 10-14 days to appear and may resemble a skin burn. "Burns" that appear earlier may not be from radiation but rather from thermal or chemical exposure associated with the event. The severity of the burn increases with increasing dose.
Overall Dose Assessment
All of the above signs, symptoms, and tests can be used to provide an estimate of dose (Table 6.6). Dose assessment is an ongoing process that should include the techniques described above, as well as others recommended by experts. Close attention to dosimetric clues will eventually lead to a reasonably accurate estimate of dose. As the saying goes among health physicists, "Eventually the patient will tell you the dose."
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Medical Diagnosis: External Contamination
External contamination with radionuclides can occur in the same settings and situations that cause internal contamination. Any person who simply passes through a contaminated area without appropriate personal protective equipment (PPE), as well as any person who is injured in a contaminated area, will become externally contaminated. Civilians, emergency responders, and military personnel can encounter radionuclides both in peacetime and while waging the war on terrorism. Accidents in medical, industrial, institutional, military, and nuclear research and nuclear power settings can cause external contamination, as could an RDD (e.g., dirty bomb) or nuclear detonation. The largest amount of fallout is on the surface of the ground, so children and crawling infants are particularly prone to pick up this material on their bare skin.
Contaminated materials present as solid particulate matter or liquids that are on the ground or exposed surfaces. Health physicists have described these contaminants as "radioactive dirt" that can be washed off skin and hair. Radionuclides can be deposited on the skin and into body orifices during the immediate event or afterward through contact with contaminated surfaces or liquids. Liquids that contain radioactive materials can readily penetrate body orifices and non-protective clothing, allowing contamination of other external areas or internal contamination by absorption or ingestion. However, up to 95% of contamination is on the outer clothing and shoes. The body surfaces most likely to be contaminated include the hands, face, lower legs, and oral and nasal cavities.
Most radioactive contaminants will be alpha- and beta-particle emitters. Alpha particles do not penetrate the skin but can be a significant source of internal contamination. Beta emitters can cause full-thickness skin damage and subsequent scarring (so-called "radiation burns") when decontamination is delayed or performed improperly. Any radionuclide that emits a high level of gamma radiation can cause whole-body irradiation and ARS in a contaminated victim.
Protection of Medical and Emergency Personnel
Assessment and care of externally contaminated patients pose little to no risk to emergency or medical personnel. Proper technique and correct PPE allow medical personnel to treat radiation patients without fear of medical consequences to either themselves or the patient. First responders and hospital emergency department personnel may assume that care of such patients is dangerous, but history suggests otherwise. There has never been a major exposure among U.S. medical personnel treating radiation victims, with all measured secondary exposures being 14 mRem (0.14 mSv) or less. This dose of radiation is well within occupational standards. High-energy isotopes that pose an immediate medical threat can be detected at safe distances using radiation survey instruments (e.g., RADIACs).
As with all other patients who present for emergency care, life-threatening complications should be addressed first. External contamination with radioactive agents is unlikely to cause acute injury, so emergency resuscitation and treatment of injuries come first. This is in contrast to external contamination with chemical agents, in which rapid decontamination may be more important. Emergency treatment should not be delayed out of fear of secondary contamination of health care providers because a living patient is unlikely to be a direct threat to health care personnel. The patient has already received a radiation dose several orders of magnitude higher than any caregiver, given that the patient is in direct contact with the contaminants for the longest time.
Decontamination can begin during emergency care but only after the patient is stable. Simply removing contaminated clothing will significantly reduce the subsequent exposure. For a decontamination technique, go to the section on medical treatment later in this chapter.
Recommended steps for patient evaluation are as follows:
- Address life-threatening conditions and significant injuries.
Note: External contamination has no early signs or symptoms.
- Disrobe the patient and provide a clean gown and foot covers.
- Obtain a history; this is crucial.
- What happened during the event?
- Where was the casualty?
- What has been done since the event that would change patient contamination status?
- Conduct an initial survey with RADIACs.
- Collect samples—external swabs/swipes (orifices, wounds, "hot" areas).
- Begin external decontamination.
Diagnosis of external contamination is usually revealed by medical history. A history of some exposure event, together with suspicion of contamination, should lead medical personnel to check the patient with detection instruments. External contamination would probably be asymptomatic at this time, unless the presenting complaint is a skin lesion occurring a considerable time after the incident.
Initial Survey and Samples
External monitoring and sample collection should begin at the accident scene if possible. This use of monitoring equipment to search for radioactivity is termed a radiological survey. This readily detects external contamination and guides decontamination efforts. First responders can be quickly taught basic survey techniques from health physicists, who are experienced users of survey equipment.
The initial survey involves passing a RADIAC slowly over the entire body, using both alpha- and beta-gamma detectors. The RADIAC should be moved slowly from head-to-toe and side to side, at a rate of about 2-3 cm/sec, and the number of counts/minute should be recorded frequently. At any site that has a high count (i.e., "hot"), a smear sample should be collected, or the area should be "swiped" using gauze or filter paper. These samples should be saved individually in suitable specimen containers for later laboratory analysis (go to the section on medical treatment later in this chapter).
Evaluation of Wounds and Orifices
Wounds and orifices should also be surveyed to see if decontamination of these sites is indicated. All wounds should be surveyed with RADIAC, because wounds are more likely to be contaminated than intact skin. A "swipe" sample should be collected from any wound with a high count. Wounds should be uncovered and exudates removed/collected before the survey, because dressings and exudates can block alpha particles and low-energy beta particles. Wounds should be dried by application of absorbent material, rather than by rubbing with gauze, which can force contaminants into the tissue.
Contaminants can be naturally cleared from the mouth and nose within about an hour. Therefore, nasal and oral swabs must be collected in the first hour. These should be collected at the accident scene if possible but certainly before the patient is washed or showered. Both nostrils should be swabbed and activity on the swab measured with the RADIAC. The swabs should be saved. Contamination of only one nostril means that the patient has touched his nose with contaminated hands, or that there is unilateral nasal obstruction. Samples of saliva, sputum, and vomitus should also be collected if available.
After each decontamination, all the above RADIAC surveys should be repeated, taking additional samples if there is residual radioactivity. Each sample should be labeled with the patient's identification, the sample site, and the date and time of sample collection.
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