Radiation Injuries and Vesicant Burns

Radiation Injury: Introduction

In the aftermath of 9/11 and more recent acts of unrelenting terrorism, such as the mass killings in Paris, Brussels, and Orlando, the possibility of the use of nuclear weapons or crude nuclear devices in attacks on nuclear facilities and use of chemical agents cannot be ignored. Given the devastating medical consequences that would follow the use of such weapons, the training of medical personnel will be a crucial factor in the effective management of such casualties if the unthinkable ever occurs.

Only 4 months after Roentgen reported the discovery of X-rays, Dr. John Daniel observed that irradiation of his colleague's skull caused hair loss. Since this finding was reported in 1896, many biomedical effects of radiation have been described. Knowledge of nuclear physics was rapidly amassed in the early part of the 20th century, leading eventually to the Manhattan project and the development of the atomic bomb. The use of this weapon over Japanese cities Hiroshima and Nagasaki in 1945 with at least 129,000 direct casualties and an extended amount of long-term sequelae stands as the most gruesome demonstration of the impact and threat that nuclear weapons hold. The past 50 years has also seen widespread deployment of energy-generating nuclear reactors and the expanding use of radioactive isotopes in industry, science, and health care. In 2011, a tsunami following an earthquake near the Fukushima 1 power plant in Japan led to severe equipment failures and three nuclear meltdowns and the release of radioactive material with contaminative consequences. This incidence was preceded by other major industrial accidents of note at Three Mile Island in Pennsylvania, Chernobyl in the Ukraine, and Goiania, Brazil, all of which have resulted in potential or real radiation injuries to hundreds of people. According to the latest National Council on Radiation Protection & Measurements report on radiation exposure to United States citizens, the most significant increase in ionizing radiation exposure, over the past 20 years, has been through medical imaging.

Exposure to ionizing radiation can follow one of three patterns:

• 1.

  Small-scale accidents, or cumulative exposures, as might occur in a laboratory or from an X-ray device in a hospital setting

• 2.

  Large industrial accidents (such as those mentioned above), stretching the need for treatment beyond available resources

• 3.

  Detonation of a nuclear device in a military conflict in which resources are totally overwhelmed or unavailable and associated multiple and combined injuries also exist.

Terminology

Damage to biological tissue by ionizing radiation is mediated by energy transference. This can be the result of exposure to electromagnetic radiation (e.g., X-rays and gamma rays) or particulate radiation (e.g., alpha and beta particles or neutrons). The severity of tissue damage is determined by the energy deposited per unit track length, known as linear energy transfer (LET). Electromagnetic radiation passes through tissue almost unimpeded by the skin and is called low LET because little energy is left behind. In contrast, neutron exposure has high LET, resulting in significant energy absorption within the first few centimeters of the body. Alpha and low-energy beta particles do not penetrate the skin and represent a hazard only when internalized by inhalation, ingestion, or absorption through a wound.

The biological effect of ionizing radiation is measured by the radiation absorbed dose (rad). The newer SI unit of absorbed dose is the gray (1 Gy = 100 rad). Not all radiation is equally effective in causing biological damage, although it may cause the same energy deposition in tissue. For example, 1 Gy of neutron radiation will not have the same effect as 1 Gy of gamma or X-radiation. For this reason, a unit of dose equivalence was derived that allows radiations with different LET values to be compared. One such unit is the rem (acronym of roentgen equivalent man). The dose in rem is equal to the dose in rads multiplied by a quality factor (QF). The QF takes into account the LET and has a different value for different radiations; for X-rays, it is 1.0, and for neutrons, it is 10. The international unit, now more widely in use, is the sievert (Sv). One sievert equals 100 rem; 1 rem equals 10 mSv. This allows radiations with different LET values to be compared because 1 Sv of neutron radiation has the same biological effect as 1 Sv of low LET gamma or X-radiation.

Incidence

The source of the most abundant type of biologically relevant electromagnetic radiation is the sun. Ultraviolet (UV) light with a wavelength of 315–400 nm (UVA), 280 to 315 nm (UVB), and 10–280 nm (UVC) would normally be absorbed by 98% in the atmosphere's so-called ozone layer, which extends at about 20 miles above sea level. However, mostly because of human-made pollution and the resulting increase in local permeability of this protective layer, UV radiation can reach the surface of the skin and unfold its hazardous effects. Although not technically ionizing, UV light can severely irritate dermal structures in terms of first- and second-degree burns. Simultaneously, the formation of pyrimidine dimers in the DNA of dermal cells can be induced, which in the long term can result in malignancies.

A significant radiation accident is one in which an individual exceeds at least one of the following criteria:

• ▪

  Whole-body doses equal to or exceeding 25 rem (0.25 Sv)

• ▪

  Skin doses equal to or exceeding 600 rem (6 Sv)

• ▪

  Absorbed dose equal to or greater than 75 rem (0.75 Sv) to other tissues or organs from an external source

• ▪

  Internal contamination equal to or exceeding one-half the maximum permissible body burden (MPBB) as defined by the International Commission on Radiological Protection (this number is different for each radionuclide)

• ▪

  Medical misadministration provided it results in a dose or burden equal to or greater than the criteria listed above.

Radiation accidents within the United States should be reported to the federally funded Radiation Emergency Assistance Center/Training Site (REAC/TS), where a Radiation Accident Registry System is maintained. It is operated by Oak Ridge Institute for Science and Education (ORISE) at Oak Ridge, Tennessee, and can be contacted by calling 865-576-1005 (website: http://orise.orau.gov/reacts ). An emergency response team of physicians, nurses, health physicists, and support personnel provides consultative assistance on a 24-hour basis and has the capability of providing medical advice or treatment whenever a radiation accident occurs. If an accident involving radiation occurs outside the United States and local resources fall short in providing immediate advice, the REAC/TS hotline can be consulted internationally as well. The International Atomic Energy Agency (IAEA) provides a detailed publication concerning the immediate actions that should be taken in the event of large-scale radiation accidents, which can be found at http://www-ns.iaea.org/tech-areas/emergency/iec/frg/default.asp .

The number of accidents, the number of persons involved, and the number of fatalities, in the United States and worldwide are shown in Table 41.1 . There have been a total of 128 fatalities recorded by the Registry worldwide (Dainiak N, personal communication and unpublished data, 2010). The majority of the radiation deaths occurred as a result of the Chernobyl accident in 1986 (>40). The classification of radiation accident by device for the period 1944 until 2016 is shown in Table 41.2 .

The majority of radiation accidents involve radioactive sources used for industrial radiography. The next most frequent accidents are radioisotope accidents involving unsealed radioactive materials, such as tritium, fission products, radium, and free isotopes used for diagnosis and therapy. Uncommon criticality accidents occur when enough fissionable material, such as enriched uranium, is brought together to produce a neutron flux so high that the material undergoes a nuclear reaction.

The most devastating radiation injuries and fatalities yet seen, however, resulted from detonation of nuclear weapons at Hiroshima and Nagasaki during World War II. Since 1945, nuclear weapon technology has developed enormously, and current strategic thermonuclear warheads dwarf the weapons used in Japan. The majority of radiation exposure occurred within the first minute of the explosion. There were no deaths attributed to the products left behind by the atomic explosions. As detailed by Kucan in 2004, the majority of radioactive fallout from these weapons was dispersed into the atmosphere because both were detonated several thousand feet in the air.

Perhaps a more likely weapon of terrorism will involve the use of a radiological dispersal device (RDD). The term “dirty bomb” generally refers to a conventional explosive packaged with radioactive material that is scattered over a wide area when detonated. It is believed that these devices would probably elicit more harm by public fear and panic than by serious injury.

In clinical practice, there are concerns that relatively low levels of radiation delivered over a long period of time might induce cancer or exert genetic or teratogenetic effects. Although most of the literature that explores this issue refers to case studies, it confirms that exposure at a younger age increases the risk of cancer. Even more important, this risk is not reduced with time. Exposure to radiation through computed tomography imaging is now commonplace, and healthcare personnel should not disregard the cumulative effects of these examinations, which can approximate levels seen in atomic bomb survivors (30 mSv). Because distance and radiation intensity obey the inverse square law, radiation dose can be limited most effectively by increasing the distance from the source of radiation. Although the efficacy of shielding devices will be determined by the type and thickness of the material and the energy and type of radiation, Table 41.3 illustrates the effectiveness of these devices when used at diagnostic X-ray energies.

Cumulative doses of radiation can be recorded on radiation badges containing photographic emulsion. The personnel dosimeter is relatively cheap and accurate but has limitations. The smallest exposure that can be measured is 10 millirem; film badges can be exposed by heat, giving false readings, and they are analyzed only at monthly intervals.

Pathophysiology

The detonation of a nuclear device over a population center will produce an extremely hot, luminous fireball, which emits intense thermal radiation capable of causing burns and starting fires at considerable distance. This is accompanied by a destructive blast wave moving away from the fireball at supersonic speed and the emission of irradiation, mainly gamma rays and neutrons. The result of a combination of thermal and radiation injuries can have a synergistic effect on the outcome. Several animal experiments have demonstrated a significant increase in mortality rate when a standard burn wound model is irradiated, over and above that expected from either injury alone.