Chapter 11
IONIZING RADIATION

James P. Seward*

Although most physicians and other healthcare professionals do not often encounter individuals injured by ionizing radiation in their practices, they can anticipate questions about radiation exposure and its potential health effects. In the rare event that a patient does present following radiation exposure or contamination with radioactive materials, the following information will be of assistance in the individual’s case management. Important information on resources for emergency information and expert advice are included at the end of this chapter.

BACKGROUND RADIATION

Although this chapter is generally concerned with unusual high exposures to ionizing radiation, routine low-level exposure to radiation is unavoidable. Background radiation is the primary source of most individuals’ exposure during their lifetimes. Background radiation has both a natural and an artificial (“human-made”) component. In the United States the population average for total natural and human-made background is approximately 6.2 mSv/year (620 mrem). Worldwide the range of natural background radiation varies considerably from 1 to 10 mSv with an average of about 2.4 mSv. Radon accounts for about one half of the dose globally. In the United States natural background is typically somewhat higher at about 3.1 mSv due to higher radon levels. Cosmic radiation, terrestrial sources (e.g., thorium and uranium), and internally deposited radionuclides (e.g., potassium-40 and carbon-14) make up the other principal sources of natural background dose. These background exposures vary with geography and altitude1,2 (http://www.nrc.gov/about-nrc/radiation/around-us/doses-daily-lives.html).

Human-made radiation usually comes principally from medical sources. This component has been growing in many parts of the world, particularly in the United States, where human-made background is about 3.1 mSv (equivalent to natural background). Other artificial sources include consumer products (0.1 mSv/0.01 rem) and a very small component (<0.01 mSv/0.001 rem) due to occupational exposure, nuclear power, or radioactive fallout. Clearly, personal medical factors, choice of residence, and occupation can be significant factors in determining this component of background exposure (see Figure 11.1).

Pie graph illustrating sources of natural and manmade background radiation depicting radon and thoron at 37% (lighter shade) and medical procedures at 36% (darker shade).

FIGURE 11.1 Sources of Natural and Manmade Background Radiation.

Source: NCRP Report No. 160(2009). Full report is available on the NCRP web site at www.NCRPpublications.org.

OCCUPATIONAL EXPOSURES

Exposure to ionizing radiation can occur in a number of different industries and industrial settings. Subsequent sections of this chapter will discuss the potential acute and chronic health effects. For many occupational groups there is a substantial body of epidemiologic literature that is definitive in a few situations where doses are high but is more often inconclusive. Accurate estimation of lifetime occupational dose is often challenging. It is beyond the scope of this chapter to review industry-specific findings in detail. Examples of occupational groups in which radiation-induced carcinogenesis has been demonstrated epidemiologically would include uranium miners (in the United States), nuclear remediation workers (at Chernobyl), and some other nuclear industry workers (e.g., at Mayak in Russia). Reviews of occupational exposures in relation to cancer causation may be found in References 1 and 3.Table 11.1 provides a partial listing of occupations where ionizing radiation exposure may be present.

TABLE 11.1 Examples of potential occupational exposure to ionizing radiation beyond US EPA 1 mSv limit set for general publica.

Airline pilots and crew
Food irradiation facilities
Hazardous waste management
Manufacture of consumer products (e.g., luminous dials, as mantles)
Nuclear power/fuel cycle operators
Nuclear medicine
Research involving ionizing radiation sources/radionuclides
Uranium mining and milling
Use of X-ray equipment
  Dentists and dental technicians
  Industrial radiographers
  Radiologists and X-ray technicians

a Listing does not necessarily imply documented health effects for these groups (see text).

DIAGNOSTIC MEDICAL EXPOSURES

Patient exposure has been growing with increased reliance medical procedures that utilize ionizing radiation, including both diagnostic and therapeutic uses of radiation sources. Between 1982 and 2006 the average per capita dose from medical exposure in the United States increased by 600% from 0.54 to about 3.0 mSv. The increase was largely due to CT scanning.4 Tables 11.2 and 11.3 illustrate examples of selected diagnostic radiology procedures and provide an estimate of the typical associated radiation dose. Epidemiologic studies of groups that have received high doses in the past (e.g., radiotherapy, ankylosing spondylitis cohorts) have shown the potential for medical therapy using ionizing radiation to induce cancers. There is concern that patients receiving multiple diagnostic procedures with X-ray may be at increased risk for cancer. In the absence of definitive studies, this concern is based primarily on the assumption of linear no-threshold dose–response for cancer (see Pathophysiology and Health Effects, p. 181). As a protective response, many professional medical organizations are placing increased emphasis on “Choosing Wisely” to weigh the benefit and potential harm of diagnostic procedures before ordering them. Helpful information for patients and providers related to many imaging studies can be found at http://www.choosingwisely.org. Improvements in technology and procedural technique have been lowering the doses received in many specific diagnostic procedures in recent years.

TABLE 11.2 Estimates of Effective Dose from Common Single X-rays.

Source: Reproduced with permission of Health Physics Society Outreach, http://hps.org/physicians/documents/Doses_from_Medical_X-Ray_Procedures.pdf

Estimates of the dose an individual might receive from one x ray.
Single Radiograph Effective Dose, mrem (mSv)
Skull (PA or AP)1 3 (0.03)
Skull (lateral)1 1 (0.01)
Chest (PA)1 2 (0.02)
Chest (lateral)1 4 (0.04)
Chest (PA and lateral)2 6 (0.06)
Thoracic spine (AP)1 40 (0.4)
Thoracic spine (lateral)1 30 (0.3)
Lumbar spine (AP)1 70 (0.7)
Lumbar spine (lateral)1 30 (0.3)
Abdomen (AP)1 70 (0.7)
Abdomen3 53 (0.53)
Pelvis (AP)1 70 (0.7)
Pelvis or hips3 83 (0.83)
Bitewing dental film3 0.4 (0.004)
Limbs and joints3 6 (0.06)

1 Wall BF, Hart D. Revised radiation doses for typical x-ray examinations. The British Journal of Radiology 70:437–439; 1997(5,000 patient dose measurements from 375 hospitals).

2 National Council on Radiation Protection and Measurements. Sources and magnitude of occupational and public exposures from nuclear medicine procedures. Bethesda, MD: National Council on Radiation Protection and Measurements; NCRP Report 124; 1996.

3 United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation, Vol. 1: Sources. New York, NY: United Nations Publishing; 2000.

TABLE 11.3 Estimates of Effective Dose from Complete X-ray Procedures.

Source: Provided Courtesy of the Health Physics Society, http://hps.org/physicians/documents/Doses_from_Medical_X-Ray_Procedures.pdf

Estimates of the dose an individual might receive if undergoing an entire procedure (e.g., a lumbar spine series typically consists of five films).
Complete Exams Effective Dose, mrem (mSv)
Intravenous pyelogram (kidneys, 6 films)1 250 (2.5)
Barium swallow (24 images, 106 sec fluoroscopy)1 150 (1.5)
Barium meal (11 images, 121 sec fluoroscopy)1 300 (3.0)
Barium follow-up (4 images, 78 sec fluoroscopy)1 300 (3.0)
Barium enema (10 images, 137 sec fluoroscopy)1 700 (7.0)
CT head1 200 (2.0)
CT chest1 800 (8.0)
CT abdomen1 1,000 (10)
CT pelvis1 1,000 (10)
CT (head or chest)2 1,110 (11.1)
PTCA (heart study)3 750–5,700 (7.5–57)
Coronary angiogram3 460–1,580 (4.6–15.8)
Mammogram3 13 (0.13)
Lumbar spine series3 180 (1.8)
Thoracic spine series3 140 (1.4)
Cervical spine series3 27 (0.27)

1 Wall BF, Hart D. Revised radiation doses for typical x-ray examinations. The British Journal of Radiology 70:437–439; 1997(5,000 patient dose measurements from 375 hospitals).

2 National Council on Radiation Protection and Measurements. Sources and magnitude of occupational and public exposures from nuclear medicine procedures. Bethesda, MD: National Council on Radiation Protection and Measurements; NCRP Report 124; 1996.

3 United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation, Vol. 1: Sources. New York, NY: United Nations Publishing; 2000.

MEASUREMENT ISSUES AND THE PHYSICS OF IONIZING RADIATION

Exposure to ionizing radiation can be delivered either by electromagnetic radiation (X-rays and gamma rays) or by moving particles (alpha and beta particles, neutrons, and protons). The physical characteristics of these types of radiation are reviewed in Table 11.4.

TABLE 11.4 Types of ionizing radiation important to radiologic health.

Source Symbol Character Massa Charge Example
X-ray X Electromagnetic energy 0 0 X-ray tube
Gamma γ Electromagnetic energy 0 0 60 Co 192 Ir
Alpha α Particulate (helium nucleus) 4 ++ 239 Pu 212 Po
Beta β Particulate (electron) 1/2000 90 Sr 3 H
Neutron n Nucleus particle 1 0 235 U fission
Proton p Nucleus particle 1 + Proton beam

a The atomic mass unit (AMU) is chosen so that a neutral carbon-12 atom has a relative mass exactly equal to 12. This is equal to ~1 AMU for both a proton and a neutron.

The basic unit of radiation exposure is the gray (Gy) given in international system (SI) units or the rad (given in traditional units). Since some types of ionizing radiation are more effective at causing ionization than others, a second measure called the dose equivalent is used to adjust for the tissue damage caused by the exposure. The unit is the sievert (Sv) in SI units or rem in traditional units. The dose equivalent is obtained by multiplying the radiation dose by a quality factor (also called weighting factor). For X-rays, gamma rays, and electrons, the quality factor equals 1, and 1 rad equals 1 rem. For alpha particles, the quality factor is 20; so, 1 Gy of alpha dose equals 20 Sv. Table 11.5 shows the units of radiation and radioactivity. There is an ongoing effort on the part of the scientific community to regularly use SI units of becquerel, gray, and sievert.5 Scientific publications commonly require that units be given in SI units. As with conversion of measurements to metric terms, use of the older terminology persists. Both units will be used here to facilitate familiarity with them.

TABLE 11.5 Units of radiation and radioactivity.

Unit description Unit name Symbol Definition
Activity Curie Ci 3.7 × 1010 disintegrations/s
Becquerel Bq 1 disintegration/s
Exposure Roentgen R 2.58 × 10−4 C/kg
Absorbed dose Rada rad 100 ergs/g of absorbing material
Gray Gy 100 rad
Dose equivalent Remb rem rad × Q (quality factor)
Sievert Sv 100 rem

Measurement terminology: 1000 millicuries in 1 curie; 1 000 000 microcuries in 1 curie
1 000 000 000 nanocuries in 1 curie; 1 000 000 000 000 picocuries in 1 curie
1 000 000 000 000 000 femtocuries in 1 curie
1 curie = approximate disintegration rate of 1 g of 226 Ra or 3.7 × 1010 disintegrations per second

a Radiation absorbed dose.

b Roentgen equivalent man.

The penetration of radioactive dose in the body depends on the energy and, in the case of particles, the mass; the more massive the particle, the less distance it travels in the body. Since the relatively massive, positively charged alpha particles do not penetrate the skin or clothing, they are primarily a concern if deposited internally.

Beta particles (electrons) can penetrate the skin to the germinal layer of the epidermis, and beta-emitting contaminants that are allowed to reside on the skin for significant periods can cause dermal injury. Beta radiation can travel several feet in air. Gamma radiation and X radiation are highly penetrating to human tissue and require dense shielding materials. Uncharged neutron particles can be relatively penetrating and damaging and, therefore, have a quality factor up to 20 depending on their energy. It is important to recognize that radioactive sources often emit more than one type of ionizing radiation.

Ionizing radiation can be detected by a number of devices, but personal dosimeters are the instrument of choice to record individual exposures. Film badges have been almost completely replaced by thermoluminescent dosimeters (TLDs) (Figure 11.2). TLDs use materials (most commonly lithium fluoride) that glow on heating after exposure to ionizing radiation. TLDs are useful to detect beta and gamma radiation. Polycarbonate “foils” are often incorporated into TLDs to detect neutrons. Neutrons disrupt the structure of the polycarbonate, and these trails can be visually counted under a microscope after “etch” development.

Photo displaying the interior of a thermoluminescent dosimeter (TLD) with areas for beta, gamma, and neutron detection.

FIGURE 11.2 Interior of a thermoluminescent dosimeter (TLD), showing areas for beta, gamma, and neutron detection.

Alpha particles cannot be counted directly with a dosimeter, but they can be identified by their associated low-energy gamma emissions. Special thin-window Geiger–Müller counters can directly measure surface alpha contamination. Whole-body counters are very sensitive gamma cameras that identify the low-energy gamma coemissions from internally deposited alpha emitters.

EXPOSURE GUIDELINES

Dose limits for ionizing radiation have been established for occupationally exposed individuals and for the general public. These limits are based on recommendations of the National Council on Radiation Protection and Measurements (NCRP).6 The dose limits that have been established by the Nuclear Regulatory Commission (NRC) and the US Department of Energy (DOE) reflect the findings and recommendations of this advisory group. The resultant dose limit guidelines are outlined in Table 11.6. Whole-body exposure limits have been established to reduce the risk of cancer. The annual risk of a fatal radiation-induced cancer in a population from exposure at the annual allowable limit of 50 mSv (5 rem) is approximately 1 in 10 000.

TABLE 11.6 Ionizing radiation exposure guidelines for the United States.

Category Dose limit guidance (NRC, DOE, NCRP)
mSv rem
Occupational exposure (annual) 50 5
Lens of the eye 150 15
Skin, other organs/tissues 500 50
Unborn child of worker 5 0.5
Members of the public (annual) from a licensed nuclear operation 1 0.1

DOE, Department of Energy (see 10 CFR 835); NCRP, National Council on Radiation Protection (see Report 116); NRC, Nuclear Regulatory Commission (see 10 CFR 20).

The NCRP also recommends a cumulative dose limit of 10 mSv (1 rem) × age. Workers exposed at this average limit would have a cumulative lifetime risk of a fatal radiation-induced cancer between 1 per 1000 and 1 per 10 000. The International Commission on Radiological Protection (ICRP) has recommended lowering the current recommended standards on the basis of the reevaluation of the atomic bomb survivor cohorts from Japan.7 Their recommendation calls for a maximum of 100 mSv (10 rem) exposure over 5 years, with a yearly average exposure of 20 mSv (2 rem). These recommendations have not yet been incorporated into US NRC or DOE exposure standards.

To reduce the potential for in utero developmental effects on the fetus, both NRC and DOE standards require that occupational exposure of a pregnant worker must not exceed 5 mSv (0.5 rem) during the entire gestation period. There are also separate dose limits for exposure to the skin, extremities, the lens of the eye, and any specific body organ in order to prevent dose-related deterministic effects.

In the United States an Occupational Safety and Health Administration (OSHA) standard for ionizing radiation use in general industry is found in 29 CFR 1910.1096, and the exposure limits are summarized in Table 11.7. OSHA incorporates applicable NRC standards for protection against radiation exposure in its Construction (29 CFR 1926.53) and Shipyard Employment (29 CFR 1915.57) Standards.

TABLE 11.7 US federal OSHA radiation exposure limits under 29 CFR 1910.1096.a

rem per calendar quarter
Whole body: head and trunk; active blood-forming organs; lens of eyes; or gonads 1 1/4b
Hands and forearms; feet and ankles 18 3/4
Skin of whole body

a Activities carried out by Department of Energy facilities or under license by the Nuclear Regulatory Commission have separate regulations.

b An employer may permit an individual in a radiation restricted area to receive doses to the whole body greater than those above so long as:

  • During any calendar quarter the dose to the whole body shall not exceed 3 rem.
  • The dose to the whole body, when added to the accumulated occupational dose to the whole body, shall not exceed 5(N − 18) rem, where “N” equals the individual’s age in years at his last birthday.

Exposure standards for underground miners have been developed to limit exposure to alpha-emitting radon progeny. Exposure is measured in working level months (WLM). A working level (WL) is any combination of short-lived radon progeny (for radon-222: polonium-218, lead-214, bismuth-214, and polonium-214; and for radon-220: polonium-216, lead-212, bismuth-212, and polonium-212) in 1 L of air that will result in the ultimate emission of 1.3 × 105 MeV (megaelectron volts) of potential alpha particle energy. A WLM is 170 hours of exposure at one WL. Under US federal standards enforced by the Mine Safety and Health Administration, the annual exposure limit is 4 WLM for an individual worker.

A general principle for all potential exposure situations is that every effort must be made to limit exposure to ionizing radiation to a level that is as low as reasonably achievable (ALARA). This means that radiation exposures must be kept as low as possible while still allowing workers to get their jobs done.

PATHOPHYSIOLOGY AND HEALTH EFFECTS

Ionizing radiation consists of electromagnetic waves or moving particles that carry sufficient energy to produce ions in matter. Ionization occurs when enough radiation energy transfers to atoms in the material through which it is passing to displace an orbital electron, thus leaving these atoms as electrically charged ions. In tissue, ionization can cause cellular injury, leading to apoptosis, mutagenesis, carcinogenesis, and cytogenetic changes. DNA damage may include single- and double-strand breaks. Mechanisms of injury may also include the generation of reactive oxygen species and the bystander effect in which agents or signals from irradiated cells reduce survival in surrounding cells.

The spectrum of health effects from ionizing radiation can be divided into the stochastic and nonstochastic (also called deterministic) effects. While most deterministic effects occur within days or weeks of exposure, a few, such as increases in cardiovascular disease, are delayed. The nonstochastic effects are those that appear predictably as a function of the dose received and worsen with increasing dose. The stochastic effects, including cancer and the theoretical risk of birth defects, are “probabilistic.” They may or may not occur in an individual as a result of an exposure, but the risk in a population of similarly exposed individuals increases with the dose.

Nonstochastic (deterministic) effects

All organs can undergo nonstochastic, dose-dependent effects from radiation exposure. In addition to acute effects, many organs may be susceptible to delayed effects that develop over months or years. Fibrosis is the most common cause of delayed organ failure. The reader is referred to additional references for detailed discussions of specific organ effects and thresholds as well as acute versus fractionated dose thresholds for organ damage.8,9

THE ACUTE RADIATION SYNDROME (ARS)

Large whole-body doses of ionizing radiation above 1 Gy (100 rad) can cause the acute radiation syndrome that is characterized by a sequence of dose-dependent organ effects. ARS may progress through four phases: prodrome, latent phase, manifest illness, and recovery or death. The time course of these phases and the need for hospitalization vary with the dose (Table 11.8).

TABLE 11.8 Signs and Symptoms of Acute Radiation Syndrome in the Three Phases after Exposure. Adapted from Diagnosis and treatment of radiation injuries. Safety series no. 2. Vienna/International Atomic Energy Agency 1998. Reprinted with Permission.

PRODROMAL PHASE OF ACUTE RADIATION SYNDROME (ARS) (WBE = WHOLE BODY EXPOSURE)
Degree of ARS and approximate dose of acute WBE (Gy)
Symptoms and medical response Mild (1–2 Gy) Moderate (2–4 Gy) Severe (4–6 Gy) Very severe (6–8 Gy) Lethala (>8 Gy)
Vomiting
Onset 2 hrs after exposure or later 1–2 hrs after exposure Earlier than 1 hr after exposure Earlier than 30 min after exposure Earlier than 10 min after exposure
% of incidence 10–50 70–90 100 100 100
Diarrhea None None Mild Heavy Heavy
Onset 3–8 hrs 1–3 hrs Within minutes or 1 hr
% of incidence <10 >10 Almost 100
Headache Slight Mild Moderate Severe Severe
Onset 4–24 hrs 3–4 hrs 1–2 hrs
% of incidence 50 80 80–90
Consciousness Unaffected Unaffected Unaffected May be altered Unconsciousness (may last seconds/minutes)
Onset Seconds/minutes
% of incidence 100 (at >50 Gy)
Body temperature Normal Increased Fever High fever High fever
Onset 1–3 hrs 1–2 hrs <1 hr <1 hr
% of incidence 10–80 80–100 100 100
Medical response Outpatient observation Observation in general hospital, treatment in specialized hospital if needed Treatment in specialized hospital Treatment in specialized hospital Palliative treatment (symptomatic only)
LATENT PHASE OF ACUTE RADIATION SYNDROME
Degree of ARS and approximate dose of acute WBE (Gy)
Mild (1–2 Gy) Moderate (2–4 Gy) Severe (4–6 Gy) Very severe (6–8 Gy) Lethal (>8 Gy)
Lymphocytes (G/L) (days 3–6) 0.8–1.5 0.5–0.8 0.3–0.5 0.1–0.3 0.0–0.1
Granulocytes (G/L) >2.0 1.5–2.0 1.0–1.5 ≤0.5 ≤0.1
Diarrhea None None Rare Appears on days 6–9 Appears on days 4–5
Epilation None Moderate, beginning on day 15 or later Moderate or complete on days 11–21 Complete earlier than day 11 Complete earlier than day 10
Latency period (days) 21–35 18–28 8–18 7 or less None
Medical response Hospitalization not necessary Hospitalization recommended Hospitalization necessary Hospitalization urgently necessary Symptomatic treatment only
CRITICAL PHASE OF ACUTE RADIATION SYNDROME
Degree of ARS and approximate dose of acute WBE (Gy)
Mild (1–2 Gy) Moderate (2–4 Gy) Severe (4–6 Gy) Very severe (6–8 Gy) Lethal (>8 Gy)
Onset of symptoms >30 days 18–28 days 8–18 days <7 days <3 days
Lymphocytes (G/L) 0.8–1.5 0.5–0.8 0.3–0.5 0.1–0.3 0–0.1
Platelets (G/L) 60–100 30–60 25–35 15–25 <20
10–25% 25–40% 40–80% 60–80% 80–100%b
Clinical manifestations Fatigue, weakness Fever, infections, bleeding, weakness, epilation High fever, infections bleeding, epilation High fever, diarrhoea, vomiting, dizziness and disorientation, hypotension High fever, diarrhoea, unconsciousness
Lethality (%) 0 0–50 20–70 50–100 100
Onset 6–8 weeks Onset 4–8 weeks Onset 1–2 weeks 1–2 weeks
Medical response Prophylactic Special prophylactic treatment from days 14–20; isolation from days 10–20 Special prophylactic treatment from days 7–10; isolation from the beginning Special treatment from the first day; isolation from the beginning Symptomatic only

a With appropriate supportive therapy, individuals may survive whole body doses as high as 12 Gy.

b In very severe cases, with a dose >50 Gy, death precedes cytopenia.

During the prodromal period the exposed individual may experience dose-dependent nausea, vomiting, diarrhea, headache, loss of consciousness, and fever. Individuals exposed at or below 1 Gy (100 rad) may not manifest any of these symptoms, while individuals with whole-body exposures above 8 Gy (800 rad) are likely to have them all. In the absence of good information on the amount of exposure, the time to onset of vomiting can be used to assess the approximate radiation dose received. Other early clinical indicators that can be used to estimate dose are the drop in the lymphocyte count and the dicentric chromosome assay. Most clinical laboratories can quickly perform the total lymphocyte count, whereas the dicentric chromosome assay is a specialized test that is only available in a few reference laboratories and requires multiple days’ turnaround time (see section “Assessment of External Ionizing Radiation Whole-Body Exposure” and also http://www.remm.nlm.gov/ars_timephases1.htm).

Prodromal symptoms usually resolve within approximately 2 days. The latent phase begins as prodromal symptoms subside and ends when (if) manifest symptoms of ARS develop. The latency period is dose dependent and may last 30 days or more with lesser levels of exposure. Patients with high levels of exposure (> 15 Gy, 1500 rad) may move quickly from prodrome to manifest illness with no latent period. During the latent phase patients may experience dose-dependent skin erythema, epilation, and a gradual reduction in hematopoietic indices.

The illness phase of ARS is often characterized by four subsyndromes affecting the hematopoietic, gastrointestinal, dermatologic, and central nervous systems (CNS) that manifest some of the most predictable health effects. However, many body organs can be affected by radiation exposure, and clinical findings are not limited to these four systems.

Radiation causes death of hematopoietic cells in the bone marrow with doses as low as 1 Gy (100 rad), resulting in a decline in white blood cell and platelet counts and delayed tissue healing. Peripheral lymphocyte counts may drop progressively in the first 24 hours, well in advance of the decline in granulocytes and thrombocytes that typically reach their nadir in 30 days. Red blood cell counts decline more slowly. Consequences of the hematopoietic system effects include increased risk of bleeding, immune dysfunction, infection, and delayed wound healing.

The gastrointestinal epithelium, with its high rate of turnover, is often affected by whole-body radiation beginning at about 6 Gy (600 rad) of exposure. A syndrome of vomiting, diarrhea, hematochezia, and malabsorption may result within hours to several days on a dose-dependent basis. Patients may have an ileus as well as fluid and electrolyte imbalances.

The skin reacts to local and whole-body exposures with a dose-dependent progression of signs including erythema, epilation, edema, dry and moist desquamation, blistering, ulceration, and necrosis; epilation may occur at doses above 3 Gy/300 rad manifesting after about 2 weeks. There may be both an early-phase and a late-phase skin erythema if the dose has been sufficient. The hours to onset of skin erythema in the first 24 hours correlates with the dose received. Dose-dependent secondary skin erythema may occur days later. Local skin exposure is one of the most frequent types of radiation injury and often results from inadvertent exposure to ionizing radiation beams.

Nonspecific central nervous system effects such as nausea and vomiting, fatigue, anorexia, and mild headache can manifest at the lower range of exposure in the ARS. More devastating CNS findings occur at high exposure levels (> 20 Gy/2000 rad) and may include early onset of severe headache and hypotension, cognitive impairment, cerebral edema, ataxia, convulsions, coma, and death within several days.

GONADAL EFFECTS

The testes (spermatogonia) are particularly sensitive to radiation; decreases in sperm counts can occur at low doses around 150 mGy (15 rad). Exposures in the range of 3–4 Gy (300–400 rad) can result in permanent sterility in men. The organ dose to create sterility in women is upward of 2–3 Gy (200–300 rad) with the follicles nearest to ovulation being the most sensitive. Lower doses can temporarily impair fertility.8

IN UTERO DEVELOPMENTAL EFFECTS

Radiation exposure of >  0.5 Gy (50 rad) to the fetus can cause growth retardation and congenital malformations. A dose-dependent relationship has been found between radiation exposure and reduced IQ in children of Japanese atomic bomb survivors who were irradiated between 8 and 15 weeks of gestation and to a lesser extent between 15 and 25 weeks. Children who were irradiated while in utero are also at higher risk from the stochastic effect of leukemia and solid cancers.

CATARACTS

Ionizing radiation can cause cataracts of the lens of the eye from acute exposures or significant smaller exposures over time. The type of lens opacity induced is usually a posterior subcapsular cataract. There is increasing evidence of cataract formation among those who conduct interventional medical radiography studies with insufficient eye protection with a threshold of approximately 0.5 Gy (50 rad) that varies with the type of radiation (neutrons more potent) and dose rate (fractionated slower).

OTHER ORGAN EFFECTS

Ionizing radiation can cause also pneumonitis that may progress into fibrosis and can be a limiting factor in long-term survival. Long-term follow-up of Japanese atomic bomb survivors and patients who received chest or head radiotherapy has demonstrated an association between cardiovascular disease and radiation exposure at doses even below 1 Sv (100 rem). Deterministic radiation effects on the vascular endothelium are a potential explanation for this increased risk. Ionizing radiation may cause acute renal failure and nephrosclerosis as well as liver injury. Both thyroid nodules and hyperparathyroidism are more common in individuals who have received radiation to the neck.

Stochastic effects

The stochastic health effects of ionizing radiation are related to mutagenic and carcinogenic events in the cell. The key demonstrated stochastic effect in humans is malignancy. Radiation-induced cancers have no special features differentiating them from other cancers. The expression of hereditary genetic effects in humans has not been found in human observational studies. However, since they have been seen in mice and other organisms, there is a possibility that human hereditary genetic effects could occur.

Knowledge about the dose–response curve for cancer comes from the study of exposed cohorts. The most intensive ongoing study is the Long-Term Survivor Study (LSS) of the Hiroshima and Nagasaki bombing victims. Examples of additional studies include research on fluoroscoped tuberculosis patients as well as patients receiving radiation therapy for ankylosing spondylitis, cervical cancer, and tinea capitis. There has been much scientific discussion on the shape of the dose–response curve, particularly at low doses (Figure 11.3). There is good evidence that the curve is linear for solid tumors at higher doses (above 100 mSv/10 rem).

Graph of different conceptual models for cancer risk from ionizing radiation dose depicting linear no-threshold (high and low dose rate), linear quadratic model, and linear model with a threshold.

FIGURE 11.3 Different conceptual models for cancer risk from ionizing radiation dose. The National Research Council Biological Effects of Ionizing Radiation VII Phase 2 report adopts the Linear No-Threshold model (noted above for high and low dose rates) as more scientifically plausible than the threshold model. The linear quadratic model was adopted for leukemias.

Source: Brenner, DJ, R. R, Goodhead DT, Hall EJ, Land CE, Little JB, Lubin JH, Preston DL, Preston RJ, Puskin JS, Ron E, Sachs RK, Samet JM, Setlow RB, Zaider M. 2003. Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know. P Natl Acad Sci USA 100:13761–13766. Copyright (2003) National Academy of Sciences, U.S.A. Reprinted with permission.

The Committee on the Biological Effects of Ionizing Radiation VII (BEIR VII) of the US National Research Council has concluded that there is a linear dose–response relationship between exposure to ionizing radiation and the development of radiation-induced solid tumors. BEIR VII assessed the health risks from exposure to low doses below 100 mSv (10 rem) and concluded that it is unlikely that a threshold exists for the induction of cancers, although the occurrence of cancers at low doses will be small.1

Recent epidemiologic evidence from the LSS of cancer incidence in those atomic bomb survivors who received low doses offers additional support for the linear no-threshold model.10,11

With respect to leukemias, the evidence supports a linear quadratic dose–response model (Figure 11.3). Leukemia was the earliest cancer attributed to radiation exposure in the LSS with a similar dose–response curve for various leukemia subtypes that were seen.2 Most sources continue to classify chronic lymphocytic leukemia as nonradiogenic based on the paucity of epidemiologic support. Leukemia can have a relatively short latency period with indications that excess cases may have occurred in atomic bomb survivors in less than 5 years.

The BEIR VII committee discounted the arguments for hormesis, the theory that low doses of radiation are beneficial in humans.

Radiation exposure has been demonstrated to increase the risk of most types of solid tumors, although there is considerable uncertainty in quantifying risk and statistical significance has not been reached for some tumors in the Japanese LSS. Thyroid, breast, bladder, colon, lung, ovary, and skin cancers are examples of solid tumors with significant excess relative risk. Excellent discussions of specific tumor sites can be found in the existing literature.1,3

Carcinogenic effects may occur from internally deposited radionuclides. Examples include lung cancer in uranium miners and osteogenic sarcomas in radium dial painters. Underground miners of uranium and other minerals have an increased incidence of lung cancer as a result of chronic exposure to radiation from inhaled radon progeny. Radon is a decay product of naturally occurring radium and uranium. Its decay in the air results in “radon progeny” or radionuclide products that emit alpha particles, which are inhaled. Because they are solid, they attach themselves to dust particles in the air that can be inhaled. The primary hazardous radiation dose from the radon progeny is due to the alpha particles that are deposited in the lungs. These particles can induce metaplasia and atypical cell growth in the tracheobronchial epithelium that may subsequently develop into bronchial carcinoma. In recognition of the demonstrated lung cancer risk among uranium miners, the Congress passed the Radiation Exposure Compensation Act in 1990 to compensate exposed uranium miners with lung cancer.

Because cigarette smoking has a synergistic effect with this radiation exposure, smokers have an increased risk of cancer, along with a decreased latency period from time of original exposure to the expression of disease.

Monitoring of ionizing radiation exposure from radon progeny in miners is based on the concept of a Working Level Month (as described in “Exposure Guidelines”).

Radon and radon progeny also pose an internal radiation hazard to the general public. Radon exposure is estimated to be the second leading cause of lung cancer in the United States after tobacco smoking. The risk of cancer in the general population is dependent on the amount of cumulative radon progeny exposure, the age distribution of the population, the time since the start of exposure, and the extent of cigarette smoking.

Radon is found in soils and trapped in basements and the lower floors of housing where significant human exposure can occur. While there is substantial geographic variation in the presence of radon, geography alone is not a sufficient predictor (Figure 11.4). State public health agencies have developed programs to encourage the public to test their homes for the presence of radon. A variety of short- and longer-term detection devices are commercially available; longer-term monitoring is preferable due to greater accuracy and seasonal variation. These screening devices are usually placed in the basement or the area of greatest risk. The EPA has developed an exposure guideline of 4 picocuries/liter of air as a threshold for remediation measures. This level is based on technical feasibility for remediation, not “zero risk” to inhabitants.12 Smokers living in homes with elevated levels of radon should be strongly supported in efforts to quit.

EPA map of radon zones depicting zone 1 (darkest shade), zone 2 (darker shade), and zone 3 (lighter shade).

FIGURE 11.4 EPA Map of Radon Zones.

Source: https://www.epa.gov/sites/production/files/2015-07/documents/zonemapcolor.pdf.

DIAGNOSIS AND TREATMENT

External ionizing radiation exposure, radionuclide contamination, and internal deposition

In the initial patient evaluation, it is important to decide whether the individual has been exposed to an energy source (irradiated) or contaminated with radioactive materials that emit ionizing radiation.

Exposure to X-ray and gamma (photon) radiation is called external exposure, because this form of radiation lacks mass and is entirely composed of electromagnetic waves. Although it may produce ionization, it does not make matter or tissue radioactive. Therefore, rescue workers dealing with these victims do not need to be concerned about receiving radiation exposure once the victim has been removed from the field of ionizing radiation exposure. However, appropriate measures must be taken to ensure emergency responder safety if the victim is in an active radiation field or contaminated with radionuclides.

Radionuclides, such as radioactive iodine (131 I) or cesium (137 Cs), have a mass that is radioactive and can become distributed on the body surface (contamination) or internally deposited in the body by way of inhalation or ingestion and through the skin by puncture, laceration, abrasion, or burn. The contaminating or internally deposited material continues to emit radiation types (e.g., alpha, beta) and amounts that are characteristic of the specific radionuclide. The radionuclide may also contaminate the surrounding area and other individuals in that area.

Assessment of external ionizing radiation whole-body exposure

Rescue workers responding to a radiation incident should remove the victim quickly from the radiation field and limit medical care for injuries to lifesaving procedures until both the rescuers and the patient are removed from the radiation exposure.

Extremely high whole-body exposures can result in an acute radiation syndrome, as described in Section The Acute Radiation Syndrome, p. 182, including the development of signs and symptoms that indicate the severity of the exposure. Prodromal acute radiation syndrome findings are summarized in Table 11.8.

It is important to gather information about the amount of exposure, either from a health physicist or from any other person who is knowledgeable about the exposure circumstances. Radiation dosimetry, if available, will also help in the management of the case. If the patient has been irradiated, the clinician should attempt to establish whether the exposure was limited to an extremity or a specific body area or whether it could be described as whole-body exposure. In addition to information gathered from experts on the scene, there are clinical indicators that can provide information about the likely dose. The timing of onset of nausea and vomiting after exposure corresponds with the dose. The amount and timing of a decline in the peripheral lymphocyte count (lymphocyte depletion kinetics) and the neutrophil/lymphocyte (N/L) ratio are also good indicators of exposure. A baseline differential white blood cell count should be performed immediately and then approximately every 4–6 hours. The USDHS Radiation Emergency Medical Management website has calculators that can convert vomiting latency and lymphocyte kinetics into dose estimates (http://www.remm.nlm.gov/ars_wbd.htm), and additional guidance on use of the N/L ratio in early assessment can be found at http://orise.orau.gov/files/reacts/medical-aspects-of-radiation-incidents.pdf.

Bioassay cytogenetic studies are another way to assess the dose received, particularly when the level of exposure is uncertain. In acute exposure situations the preferred test is the dicentric chromosome assay (Figure 11.5). This test can be performed on blood drawn as soon as 1 hour after exposure, but optimally after 24 hours if there is a sufficient pool of surviving lymphocytes. The sample should be sent to an experienced reference laboratory; it may detect exposure levels as low as 0.1–0.2 Gy (10–20 rad) and is both sensitive and specific. This procedure takes 4–5 days, but it provides useful dose information.

Micrograph displaying cytogenetic assay for dicentric chromosome, ring aberration, fragments, and normal chromosomes depicted by arrows.

FIGURE 11.5 Cytogenetic Assay for Dicentric Chromosomes.

Source: https://orise.orau.gov/files/reacts/medical-aspects-of-radiation-incidents.pdf, page 42.

A second technique of chromosome painting called fluorescence in situ hybridization (FISH) is the preferred method for retrospective (> 6 months) assessment of exposure. FISH uses chromosome-specific probes in peripheral blood lymphocytes to evaluate translocations. Since chromosome translocations are relatively stable, their frequency can be used to estimate past radiation exposures. Another technique called premature chromosome condensation (PCC) may be useful for exposures over 3.5 Gy (350 rad).13

Treatment of the acute radiation syndrome

Appropriate treatment of ARS depends on assessing the dose and the stage of the patient’s condition based on the typical sequence of the syndrome. Support of the hematopoietic system and prevention of infection are key goals to promote recovery.

Useful laboratory studies include14:

  • Complete blood count with differential (every 4–6 hours) (see above)
  • Serum amylase (baseline and serially every 24 hours) (amylase increases with dose assuming salivary glands irradiated)
  • Plasma FLT-3 ligands (correlates with radiation bone marrow injury)
  • Blood citrulline (decreases with radiation-induced bowel mucosal atrophy)
  • Interleukin-6 (indicator of high radiation dose)
  • C-reactive protein (increases with radiation dose)
  • Cytogenetic studies (see above)

Clinical interventions are tailored to the indicators of radiation injury. They may include management of nausea and vomiting with antiemetics, hospitalization, and administration of hematopoietic cell line colony-stimulating factors. The effectiveness of granulocyte and granulocyte-macrophage stimulating factors is greatest when given early—within 24–72 hours of injury.

Prevention of infection is a key objective. In addition to maintaining adequate circulating granulocytes, measures such as skin and bowel decontamination, reverse isolation, and environmental controls should be considered according to standard protocols for immune-impaired patients. Support with transfusions and antibiotics may be necessary.

Donor bone marrow transplantation (BMT) was performed on a number of the Chernobyl incident victims; however, most of these individuals died of other radiation complications or of graft-versus-host disease. Two BMT survivors were later determined to have regenerated blood cells from their own marrow, although the donor cells may have helped them to survive for this to occur.

Lung effects may be seen with doses above 8 Gy (800 rad) and include acute effects on the alveoli with cytokine-mediated inflammation. Over time pulmonary fibrosis can result.

In ARS situations with trauma or when surgery or wound closure is required for a patient, consideration should be given to performing the operation early in the course. Over time the patient’s wound healing abilities are likely to decline with the fall in hematologic cell lines.

The survival of ARS patients depends significantly on medical support. The LD50 for patients with medical support is approximately 5–6 Gy (500–600 rad) as opposed to 3.5–4 Gy (350–400 rad) without support.

Treatment of cutaneous irradiation injury

Irradiation to specific body regions often manifests as skin injury, and the effects are typically delayed in nature. Such injuries frequently result from exposure to contained sources or to X-ray or gamma ray or beta-generating devices. The higher the dose, the more quickly the physical changes are seen. For example, a dose of 20 Gy (2000 rad) may produce reddening of the skin in 2–3 hours, whereas a dose of 6–8 Gy (600–800 rad) might result in the development of erythema after 2–3 days. The extent of injury is dependent upon the energy of the radiation type that affects penetration, the dose, and the dose rate. After an accident, it may not be possible to immediately reconstruct the exposure circumstances. Local radiation injury may be observed concurrent with significant whole-body exposure, and the patient should be evaluated for ARS as discussed above. Careful clinical evaluation and observation for progressing signs and symptoms are helpful in managing cutaneous injury. Consultation with a specialist in plastic or reconstructive surgery is often indicated.

Usually, local radiation exposure is not an acute medical emergency. Symptoms and effects are frequently delayed, so there is adequate time for evaluation, supportive treatment, and consultation. Careful observation and documentation, particularly with the use of serial color photographs, also help in evaluating the progress of local injuries. Therapeutic goals include limiting the extent of tissue damage, preventing/treating infection, and managing pain.

As seen in Table 11.9, local injury may proceed through a sequence of stages, depending on the significance of the initial exposure. Stages may include erythema, epilation, moist desquamation, dry desquamation, necrosis, and healing with fibrosis/sclerosis. Skin grafting or amputation may be necessary, and there will be an increased risk of skin cancer in irradiated areas.

TABLE 11.9 Stages of Cutaneous Radiation Injury.

Source: Centers for Disease Control and Prevention http://emergency.cdc.gov/radiation/pdf/criphysicianfactsheet.pdf pp 3-5.

Grades of cutaneous radiation injury
Grade Skin dose* Prodromal stage Latent stage Manifest illness stage Third wave of erythema Recovery Late effects
I >2 Gy (200 rads) 1–2 days postexposure or not seen no injury evident for 2–5 weeks postexposure§
  • 2–5 weeks postexposure, lasting 20–30 days: redness of skin, slight edema, possible increased pigmentation
  • 6–7 weeks postexposure, dry desquamation
not seen complete healing expected 28–40 days after dry desquamation (3–6 months postexposure)
  • possible slight skin astrophy
  • possible skin cancer decades after exposure
II >15 Gy (1500 rads) 6–24 hours postexposure with immediate sensation of heat lasting 1–2 days no injury evident for 1–3 weeks postexposure
  • 1–3 weeks postexposure; redness of skin, sense of heat, edema, skin may turn brown
  • 5–6 weeks postexposure, edema of subcutaneous tissues and blisters with moist desquamation
  • possible epithelialization later
  • 10–16 weeks postexposure, injury of blood vessels, edema, and increasing pain
  • epilation may subside, but new ulcers and necrotic changes are possible
healing depends on size of injury and the possibility of more cycles of erythema
  • possible skin astrophy or ulcer recurrence
  • possible telangiectasia (up to 10 years postexposure)
  • possible skin cancer decades after exposure
III >40 Gy (4000 rads) 4–24 hours postexposure, with immediate pain or tingling lasting 1–2 days none or less than 2 weeks
  • 1–2 weeks postexposure: redness of skin, blisters, sense of heat, slight edema, possible increased pigmentation
  • followed by erosions and ulceration as well as severe pain
  • 10–16 weeks postexposure: injury of blood vessels, edema, new ulcers, and increasing pain
  • possible necrosis
can involve ulcers that are extremely difficult to treat and that can require months to years to heat fully
  • possible skin atrophy, depigmentation, constant ulcer recurrence, or deformity
  • possible occlusion of small vessels with subsequent disturbances in the blood supply, destruction of the lymphatic network, regional lymphostasis, and increasing fibrosis and sclerosis of the connective tissue
  • possible telangiectasia
  • possible skin cancer decades after exposure
IV >550 Gy (55,000 rads) occurs minutes to hours postexposure, with immediate pain or tingling, accompanied by swelling none
  • 1–4 days postexposure accompanied by blisters
  • early ischemia (tissue turns white, then dark blue or black with substantial pain) in most severe cases
  • tissue becomes necrotic within 2 weeks following exposure, accompanied by substantial pain
does not occur due to necrosis of skin in the affected area recovery possible following amputation of severely affected areas and possible skin grafts
  • continued plastic surgery may be required over several years
  • possible skin cancer decades after exposure

* Absorbed dose to at least 10 cm2 of the basal cell layer of the skin.

Especially with beta exposure.

The Gray (Gy) is a unit of absorbed dose and reflects an amount of energy deposited in a mass of tissue (1 Gy = 100 rads).

§ Skin of the face, chest, and neck will a shorter latent phase than the skin of the palms of the hands and the skin of the feet.

Therapeutic modalities that may be employed to manage the extent of the tissue damage and recovery include14:

  • Topical corticosteroids
  • Hyperbaric oxygen
  • Pentoxifylline with vitamin E
  • State-of-the-art wound care, including microvasculature imaging techniques

External and internal contamination with radionuclides

There are two ways in which a person may be exposed to ionizing radiation through direct contact with radionuclides—by external contamination (i.e., contamination of the skin or exposed body parts only) or internal deposition (i.e., by inhalation, ingestion, wounds, or burns). Both types of exposure can occur together.

EXTERNAL CONTAMINATION

Contamination incidents require prompt removal and containment of the radionuclides and measures to limit the dose received. However, life- and limb-threatening conditions take precedence over contamination evaluation and control. Early decontamination facilitates the reduction of exposure from external irradiation and reduces the risk of cross-contaminating other individuals and areas. It may also help to reduce the risk of internal deposition of radionuclides.

Most healthcare facilities have established emergency plans addressing chemical and radiologic hazards as required by the Joint Commission on Accreditation of Healthcare Organizations. Preplanning for management of patients contaminated with radioactive materials addresses the need for prompt decontamination and care of the patient as well as protection of medical personnel and facilities. Detailed guidance for this preplanning effort is available from a number of sources.15–17 None of the required supplies are highly specialized, except for the instruments used for radiation detection. These devices are operated by a radiation safety officer (RSO), who should be formally designated at all healthcare facilities where radiotherapy devices are used or nuclear medicine is practiced. If no RSO has been named based on these activities, one should be designated in the facility’s emergency plan.

The RSO should survey the patient as soon as the patient is medically stabilized to assess the location, type, and intensity of radiation contamination. The RSO or other trained individuals use specific radioactivity-detecting devices for this purpose. In most instances, radiation contamination does not pose an external radiation threat to the healthcare providers. However, they must be protected both from becoming contaminated and from internal deposition; this can usually be achieved with surgical gowns, gloves, caps, and masks. Decontamination of patients can usually be performed readily using soap or detergents and water; in the case of wounds, copious irrigation and debridement are necessary. Collection of irrigation fluids and tissues and control of instruments, drapes, and dressings also help to constrain the spread of contamination.

External radionuclide contamination alone (i.e., with no injury) requires identification of the involved skin surfaces to control and prevent spread of the contamination and to determine which areas to decontaminate. If the skin contamination is identified and removed promptly, the radionuclide is unlikely to cause damage to the skin or deeper structures.

If the skin is broken or burned, there is potential for absorption of the radionuclide through the wound. In some cases particulate matter may be found in an open lesion or be injected subcutaneously. In these cases care should be taken to remove as much of the material as is reasonably possible. On occasion the excision of wound margins, the use of a dermatologic punch, or other surgical intervention may be necessary. In such situations the benefits of removal must be weighed against the risks of the procedure.

INTERNAL CONTAMINATION

Internally deposited radionuclides require treatment based on the chemical properties of the specific radionuclide and its deposition kinetics in the body. The advice of a physician trained in treating this type of medical situation should be sought (see resources at end of chapter). Treatment of the patient with internal radionuclide contamination begins with any needed decontamination. Assessment of the route and estimates of amount of radioactive material involved and its chemical form are necessary to evaluate absorption and distribution in the body. Specialized assessment procedures such as use of nasal swabs, use of a Geiger–Müller counter on skin surfaces, and thyroid and lung and whole-body counting may be required as well as capabilities for measuring radioactive material in excreta. Thresholds for intervention with medication and other therapies depend on the potential long-term dose to the patient from decay of internally deposited nuclides.

A variety of decorporation treatments can be used for internally deposited radionuclides. These include chelation, competitive binding, enhanced urinary excretion, and enhanced intestinal excretion (Table 11.10). For example, diethylenetriaminepentaacetate (DTPA) is used to chelate internally deposited plutonium and enhance its excretion through the kidneys. This is similar to treating lead poisoning with dimercaptosuccinic acid (DMSA, also referred to as succimer). Chelation or other treatments for internal contamination must be administered as soon as possible to reduce internal deposition in the target organs. Because this is a highly specialized activity, prompt consultation with experts in the management of internal contamination cases is critical.

TABLE 11.10 Examples of decorporation therapies for internal contamination.

Radionuclides Therapy Comment
Americium, curium, plutonium, and some other transuranic radionuclides and rare earths CaDTPA or ZnDTPA May be obtained from REAC/TS (see end of chapter)
Cobalt DTPA, DMSA, EDTA, N-acetyl cysteine (all off label) DTPA preferred
Cesium, thallium Prussian blue Prussian blue is given orally and binds radionuclide in the intestine, reducing enterohepatic recirculation
Iodine KI or SSKI Success depends on early administration after exposure. See doses in Table 11.11
Strontium Aluminum hydroxide Barium sulfate and alginates are alternatives to block gastrointestinal uptake
Tritium Forced water diuresis To promote excretion
Uranium Sodium bicarbonate Alkalinize urine to promote excretion and prevent acute tubular necrosis

Administration of iodine tablets or supersaturated potassium iodide (SSKI) solution is an important prophylactic measure that can reduce the absorption of the radioactive iodine into the thyroid gland. This measure, used after fission accidents such as Chernobyl and Fukushima, reduces radioiodine deposition and subsequent risk of thyroid cancer. Because of the high affinity of the thyroid for iodine, it is important to provide the iodine doses as soon as possible after exposure (or ideally before) to saturate the iodine receptors in the thyroid gland.

The approach for radiocesium or thallium is to administer Prussian blue (ferric hexacyanoferrate/Radiogardase) orally so that ion exchange takes place in the gut during enterohepatic circulation of the radionuclide.

For tritium (heavy water) exposure the guidance is to provide fluids and potentially diuretics to hasten the excretion through the kidneys.

A comprehensive discussion of specific isotopes and interventions to minimize internal deposition can be found in NCRP Report No. 161.18 Examples of decorporation interventions may be found in Table 11.10. Doses of potassium iodide for thyroid prophylaxis are given in Table 11.11.19

TABLE 11.11 Thyroid prophylaxis doses in radiation incident involving radioiodine.

Source: US Food and Drug Administration, http://www.fda.gov/Drugs/EmergencyPreparedness/BioterrorismandDrugPreparedness/ucm072248.htm

Threshold Thyroid Radioactive Exposures and Recommended Doses of KI for Different Risk Groups
Predicted Thyroid gland exposure (cGy) KI dose (mg) Number or fraction of 130 mg tablets Number or fraction of 65 mg tablets Milliliters (mL) of oral solution, 65 mg/mL***
Adults over 40 years ≥500 130 1 2 2 mL
Adults over 18 through 40 years ≥10 130 1 2 2 mL
Pregnant or Lactating Women ≥5 130 1 2 2 mL
Adolescents, 12 through 18 years* ≥5 65 ½ 1 1 mL
Children over 3 years through 12 years ≥5 65 ½ 1 1 mL
Children 1 month through 3 years ≥5 32 Use KI oral solution** ½ 0.5 mL
Infants birth through 1 month ≥5 16 Use KI oral solution** Use KI oral solution** 0.25 mL

* Adolescents approaching adult size (≥150 lbs) should receive the full adult dose (130 mg).

** Potassium iodide oral solution is supplied in 1 oz (30 mL) bottles with a dropper marked for 1, 0.5, and 0.25 mL dosing, each mL contains 65 mg potassium iodide.

*** See the home preparation procedure for emergency administration of potassium iodide tablets to infants and small children.

Healthcare providers who manage radionuclide-contaminated victims should be properly trained in radiation protection procedures in order to avoid becoming contaminated or incurring an internal radionuclide deposition.

Psychological aspects of radiation exposure incidents

Psychological considerations are important in all accidents, but they are even more critical for victims of radiation incidents. Public fears of radiation exposure and the difficulty individuals have in assessing their level of exposure may generate anxiety or panic. Individuals at increased risk of psychological issues in a radiation incident include individuals with children, children, first responders, evacuees, and individuals with limited social support, prior trauma, or mental illness.

Healthcare personnel should actively engage patients using attentive listening skills and promoting a sense of calmness, safety, and willingness to help without false reassurances. Information about exposure and potential health consequences needs to be communicated in clear terms that convey the level of risk appropriately. Clinicians should assess the patient’s understanding of the information provided. If the victim is not adequately informed, the adverse psychological stress can be the most serious consequence of the radiation exposure or contamination.

Social stigma is also an issue that some radiation-exposed individuals have encountered. Communication with family members is important so that they do not unnecessarily perceive risk to themselves from contact with the patient. Support from mental health professionals can often be valuable for exposure victims, especially given the long-term uncertainties that may result from exposure. Radiation incidents often generate substantial interest from the media, and it may be worthwhile preparing patients for this possibility.

Nuclear power plant incidents, the public health response, and ongoing environmental exposures

Since the beginning of the nuclear age, there have been numerous situations involving unplanned human exposure to ionizing radiation, but two events that have particularly drawn attention to radiation’s public health impacts include the nuclear power plant meltdowns at Chernobyl, Ukraine, in 1986 and Fukushima, Japan, in 2011. Both events involved the release of fission products containing iodine-131 and other radionuclides. Substantial preventable exposures to I-131 occurred around Chernobyl because of delays in notification, failure to distribute iodine tablets in a timely way, and continued consumption of contaminated foods, such as dairy products. As a result there have been many cases of papillary cancer of the thyroid in the surrounding region in individuals whose exposure to the gland exceeded 0.05 Gy (5 rem). Thyroid cancer predominantly affected children and was essentially limited to people who were under 40 years at the time of exposure. Although leukemias have been seen in remediation workers at the plant, thyroid cancer is the only malignancy that has been definitively attributed to the general public to date as a result of the nuclear meltdown. The World Health Organization estimates that some children in the areas around Fukushima have also received elevated radioiodine doses and may have an increased risk of thyroid cancer. Table 11.11 shows recommended iodine dose by age, usually administered one time as soon as possible after exposure. Iodine is most likely to be effective if given as soon as possible, but there is substantial protection even 3–4 hours after exposure.19 Due to its short half-life of 7 days, I-131 is essentially gone from the environment after 90 days.

Environmental contamination from other radionuclides during a nuclear power plant meltdown can cause additional serious public health issues. In the Chernobyl and Fukushima disasters, the principal contaminants of concern, apart from radio-iodines, are cesium-137 and -134 with respective half-lives of 30.2 and 2.06 years. Strontium-90, with a half-life of 28.8 years is also a concern. Animals, seafood, and plant products take up cesium and strontium systemically. Projected exposures from external and internal radionuclides can result in unacceptable levels of risk to residents and render some districts unsafe for habitation for many years until exposure levels drop. This has occurred around both Chernobyl and Fukushima. In some areas near the Fukushima Nuclear Power Plant, washing down of surfaces, removal or remediation of soil, and other decontamination measures have reduced risk to a level deemed acceptable for rehabilitation by public health authorities. Other areas with higher levels of contaminants will remain uninhabitable for many years. Another aspect of the Fukushima disaster is the need to monitor potentially contaminated food products to keep exposure levels within regulatory limits. Some agricultural lands and fisheries have been taken out of production until safe radiation levels are reached.

PREVENTION

The principles for prevention of exposure to radiation are similar in many ways to the hierarchy of controls in other areas of occupational health including engineering measures, administrative controls, and personal protective equipment. Key protective concepts in radiation protection include use of shielding, reduction of exposure time, and distance from the source. For point sources, intensity of the exposure is inversely related to the square of the distance. Health professionals must understand the nature of the radiation source, its strength, and its capabilities to cause exposure and penetrate human tissue as well as other matter.

Regulatory exposure standards (discussed above) provide guidance to health professionals in establishing safety programs. In the United States commercial and research nuclear reactors are under the jurisdiction of the Nuclear Regulatory Commission. Other facilities using radiation or radioactive materials may be covered by regulations of the Department of Energy, OSHA, or state agencies. It is a good practice—and required under some agencies—for an institution to establish a radiation safety committee and to appoint a radiation safety officer (RSO) who is ideally a health physics professional. The RSO is responsible for the overall radiation protection program including (i) educating users about safety procedures, (ii) monitoring environmental and personal exposure, and (iii) ensuring that all recommended radiation safety policies, procedures, and controls are followed.

The use of engineering methods to protect workers against exposure is the most reliable approach. Engineering controls such as lead shielding, high-density concrete walls, and safety interlocks are used to control external radiation exposure. Glove boxes and ventilated hoods are used to prevent the exposure of individuals who handle radionuclides. Special shields might be used to protect the eyes, arms, or other body parts from exposure.

Administrative controls must be built into standard safe radiation practices. Work practices should be used that effectively manage the unseen hazards of radiation and radioactive materials. Administrative controls may reduce time of exposure in radioactive environments and limit the proximity to sources. Other practices may include the following injunctions: (i) work only in designated areas, (ii) use spill paper under radionuclide operations, (iii) never mouth-pipette; and (iv) handle all materials to prevent secondary contamination of work areas, equipment, and personnel. The institutional RSO and the radiation safety committee enforce operational policies and procedures required for licensing.

Personal protective equipment designed to avoid radionuclide contamination or internal deposition includes special clothing and respirators with appropriate filters for radionuclides that are worn only in the work area and then discarded or collected for cleaning when the worker leaves the area. The clothing to prevent contamination may include a hood, coveralls, gloves, and booties. Plastic tape is usually used to seal the areas between the gloves and the sleeves or other gaps in protective clothing. In heavily contaminated areas, a supplied air respirator or Scott air pack may be used.

Personal protective equipment for external exposures is widely used in industrial radiography and medical radiology. This equipment consists primarily of lead aprons, gloves, thyroid shields, and leaded glasses. Personal protective equipment for medical and research use of radionuclides typically includes gloves, laboratory coats, and eye/face protection.

Employees who work regularly around radiation or have the possibility of significant exposure should be monitored for exposure levels. A standard practice is for dosimeter (e.g., TLD) to be worn in the chest area of each employee who may be at risk. The dosimeters are collected and read at set intervals, that is, weekly for higher-risk exposures and monthly or quarterly for lower-risk exposures. Employees are informed of the results, and an RSO or radiation protection specialist investigates exposures greater than expected. Any worker who has reached a threshold exposure (action level) can be removed from potential exposure.

Environmental monitoring for external hazards is usually performed with fixed equipment. TLDs, continuous air monitors, or other monitoring instruments are placed outside the shielded area to ensure integrity of engineering controls. Equipment that generates X-rays must be kept in calibration. For radionuclide use, swipe samples can be taken at work areas to check for contamination.

For individuals who work with radionuclides, periodic thyroid, chest, or whole-body scanning, as appropriate, for detection of internal deposition of the radioactive material is common practice. For those who work with radionuclides that can be excreted in the urine or feces, collection and radionuclide analysis of these excretions are done on a scheduled basis. The frequency of these examinations is dependent on the type and activity of the materials used; therefore, an expert in surveillance of these materials must be consulted to set up an appropriate schedule.

Ionizing radiation should also be covered under an institutional reproductive health policy and education provided to all workers. All pregnant employees, or employees considering a pregnancy, should be voluntarily evaluated. A reproductive health assessment should be obtained as soon as possible to determine the types and levels of potential exposure. This assessment will direct any job accommodations that might be necessary. In addition, some employers increase exposure monitoring during gestation to assure that exposures are ALARA and within gestational exposure standards. In the absence of anticipated exposures above the NCRP recommended limit of 5 mSv (500 mrem) during pregnancy, it is generally not necessary to restrict workers from their usual job duties.

There is no standard practice regarding medical surveillance of workers who have radiation exposure. The decision regarding preplacement examinations, periodic evaluations, and evaluations at employment termination or transfer depends not only on the anticipated levels of exposure but also on the other tasks and risks inherent in the work. When performed, medical surveillance should be tailored to the exposures as much as possible. Risks of both deterministic and stochastic effects are very low as long as exposures are within permissible exposure limits and ALARA principles are followed. However, in some operations with significant exposure potential, medical surveillance may provide insights as to whether proper protections are being followed and detect unanticipated consequences such as skin or lens changes. Routine screening for cancer in workers with low levels of ionizing radiation exposure is not warranted other than the age- and gender-specific screenings offered to the general public. However, the NRC has adopted guidelines developed by the American National Standards Institute and the American Nuclear Society for the medical evaluation of nuclear power reactor operators to help assure their physical abilities to perform the work.20

EMERGENCY INFORMATION AND EXPERT ADVICE

The Oak Ridge Institute for Science and Education (ORISE) operates the Radiation Emergency Assistance Center/Training Site (REAC/TS). The US Department of Energy funds this facility. Expert advice and information on managing radiation accidents are available on a 24 hours/7-day-per-week basis by calling 865-576-1005. The REAC/TS also has a website at www.orau.gov/reacts/. REAC/TS provides training courses in radiation protection, as well as courses that prepare hospital and emergency personnel to manage medical response in radiation accidents. Information about these courses can be obtained on the website.

State public health departments usually have a radiation protection division that can provide guidance in setting up radiation protection programs. These professionals also help in dealing with ionizing radiation problems in industry, healthcare settings, or research and development projects. In most states, the health department radiation division is involved with licensing, auditing, inspecting, or accrediting hospitals and other facilities that use ionizing radiation equipment and materials and are not covered by the NRC. Some hospitals have a radiation safety expert on staff that may be available to answer questions or provide assistance.

References

  1. 1. National Research Council. Health risks from exposure to low levels of ionizing radiation: BEIR VII Phase 2. Washington, DC: National Academy of Sciences, 2006:189–206.
  2. 2. US Nuclear Regulatory Commission. Sources of Radiation. http://www.nrc.gov/about-nrc/radiation/around-us/doses-daily-lives.html (accessed June 20, 2016).
  3. 3. International Agency for Research on Cancer. Radiation Vol 100D. Geneva: World Health Organization Press, 2012:132–5. http://monographs.iarc.fr/ENG/Monographs/vol100D/mono100D.pdf (accessed June 20, 2016).
  4. 4. Mettler FA. Medical radiation exposure in the US in 2006: preliminary results. Health Phys 2008; 95(5):502–7.
  5. 5. National Council on Radiation Protection and Measurements. SI units in radiation protection and measurements. NCRP Report no. 82. Washington, DC: National Council on Radiation Protection and Measurements, 1985.
  6. 6. National Council on Radiation Protection and Measurements. Recommendations on limits for exposure to ionizing radiation. NCRP Report no. 116. Washington, DC: National Council on Radiation Protection and Measurements, 1993.
  7. 7. International Commission on Radiologic Protection. Recommendations of the International Commission on Radiologic Protection. ICRP Publication no. 103. Ann ICRP 2007; 37(2–4):1–332.
  8. 8. International Commission on Radiation Protection. Nonstochastic effects of ionizing radiation. ICRP Report no. 41. Ann ICRP 1984; 14(3).
  9. 9. Anno GH, Baum SJ, Withers HR, et al. Symptomatology of acute radiation effects in humans after exposure to doses of 0.5–30 Gy. Health Phys 1989; 56(6):821–38.
  10. 10. Preston DL, Ron E, Tokuoka S, et al. Solid cancer incidence in atomic bomb survivors: 1958–1998. Radiat Res 2007; 168:1–64.
  11. 11. Shore RE. Low-dose radiation epidemiology studies: Status and issues. Health Phys 2009; 97(5):481–6.
  12. 12. US Environmental Protection Agency. Radon: A Physician’s Guide. 1993. http://www.epa.gov/radon/pubs/physic.html#SOL6 (accessed May 6, 2016).
  13. 13. International Atomic Energy Agency. Cytogenetic analysis for radiation dose assessment. Technical Report Series no. 405. Vienna: International Atomic Energy Agency, 2001.
  14. 14. Sugarman SL, Goans RE Garrett AS, et al. The Medical Aspects of Radiation Incidents. Radiation Emergency Assistance Center/Training Site ORISE Revised September 25, 2013. http://orise.orau.gov/files/reacts/medical-aspects-of-radiation-incidents.pdf (accessed May 6, 2016).
  15. 15. Ricks RC. Hospital emergency department management of radiation accidents. ORAU no. 224. Washington, DC: Federal Emergency Management Agency, 1984
  16. 16. Radiation Emergency Assistance Center/Training Site (REAC/TS). Guidance for Radiation Accident Management. http://orise.orau.gov/reacts/guide/procedures.htm (accessed May 6, 2016).
  17. 17. Centers for Disease Control and Prevention. Radiation Emergency Training and Education. http://emergency.cdc.gov/radiation/training.asp (accessed May 6, 2016).
  18. 18. National Council on Radiation Protection and Measurements. Management of persons accidentally contaminated with radionuclides. NCRP Report no. 161. Washington, DC: National Council on Radiation Protection and Measurements, 2008.
  19. 19. US Food and Drug Administration, Center for Drug Evaluation and Research (CDER). Guidance: Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies. Rockville, MD: US Department of Health and Human Services, 2001. http://www.psr.org/assets/pdfs/fda-iodine-guidelines.pdf (accessed September 4, 2016).
  20. 20. American National Standards Institute/American Nuclear Society. Medical Certification and Monitoring of Personnel Requiring Operator Licenses for Nuclear Power Plants. ANSI 3.4.-2013 (Adopted by the US Nuclear Regulatory Commission).

Note

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
35.153.134.169