Description

• Radiation includes the following:
  • Electromagnetic emissions, such as x-rays, γ-rays: These are medically important due to high tissue penetration and can cause multiorgan damage.
  • Alpha (α) radiation: heavy, positively charged particles containing two protons and two neutrons. These particles have minimal penetration and are mostly hazardous if present as external or internal (ingestional/inhalational) contamination.
  • Beta (β) radiation: These are electrons: small, light, negatively charged particles; low penetrance externally but dangerous if ingested
  • Neutron: heavy and uncharged, released during nuclear detonation. Neutrons are damaging and penetrate well.
• Units of measure
  • Absorbed dose: radiation-absorbed dose (rad) or the SI unit Gray (Gy); 1 Gy = 100 rad = 1 J/kg
  • Dose equivalent: roentgen equivalent man (rem) or the SI unit Sievert (Sv); 1 Sv = 100 rem
  • For β- and γ-radiation
    • 1 Gy = 1 Sv = 100 rad = 100 rem
• When most or all of the body receives >1 Gy, ARS can occur. A chest CT, for comparison, gives 0.007 Sv or mGy (1).
• Four major stages in ARS: prodrome, latent phase, illness, and either recovery or death. The higher the radiation doses, the shorter and more severe each stage:
  • The prodrome appears within minutes to 4 days of postexposure, lasts between a few hours and a few days, and can include nausea and vomiting.
  • Latent phase lasts from hours to several weeks when an individual feels quite well.
  • Illness phase usually starts from 1st day to the 2nd week with an abrupt onset.
  • Recovery phase may take weeks to more than a month.
• Time within and progression through these stages is dependent in part on access to, and availability of, treatment and, in part, on total dose received.

Pediatric Considerations

• Infants and children are at increased risk.
• Radioactive fallout from incidents such as Chernobyl and Fukushima can include iodine-131, which can accumulate in the thyroid and increase risk of thyroid cancer.
• Potassium iodide can reduce thyroid cancer risk; give promptly if contamination with radioactive iodine (iodine-131) is suspected.

Pregnancy Considerations

• Developing fetus is at increased risk for sickness.
• Pregnant staff should not care for externally or internally radioactively contaminated patients.

Epidemiology

• Historically
  • Japan, 1945: 120,000 individuals developed ARS from nuclear explosions.
  • Marshall Islands: 7,266 people exposed to radiation because of errors in judging winds after a nuclear test in the South Pacific
  • Chernobyl accident in Ukraine 1986: Estimated 50,000 individuals received at least 0.5 Sv of exposure. There were 134 cases of confirmed ARS (1).
  • March 2011: An earthquake and tsunami caused meltdown of 3 of 6 reactors at Fukushima Daiichi nuclear power plant in Japan. 1,700 residents, who were evacuated, received an external radiation dose. 98% were <5 mSv/yr, and 10 people were exposed to >10 mSv. No deaths were reported.
• Most acute radiation injury is related to accidents or radiology procedures and radiation therapy.
• Accidents usually involve small numbers of individuals.
• Worldwide exposure (average/person/year) (2)
  • Natural (γ-rays, radon, and others): 2.4 mSv
  • Occupational (nuclear worker): 1 mSv
  • Medical (chest x-ray–CT scan, dose per exam): 0.05 to 10.00 mSv

Incidence
There have been 65 overexposed accidents and 85 overexposed people in 2010 to 2013 as per an international registry (1).

Etiology and Pathophysiology

• Radiation interactions with atoms/molecules can result in ionization and the formation of free radicals that damage tissue by disrupting chemical bonds and molecular structures in the cell. Damage to DNA is most pathophysiologically relevant.
• Radiation damage can lead to cell death; cells that recover may be mutated and at higher risk for subsequent cancer. Cell sensitivity increases as the replication rate increases and the cell differentiation decreases.
• Bone marrow and mucosal surfaces of the GI tract (high mitotic activity) are more sensitive to radiation than slowly dividing tissues, such as muscle or bone.
• Nonionizing radiation, such as microwaves and infrared, can cause heating of tissues: testes, eye.
• Ionizing radiation: damage to DNA affecting rapidly dividing cells (GI mucosa, bone marrow, vascular endothelium, reproductive organs)
• Routes of exposure
  • Irradiation
  • External contamination (clothing, skin)
  • Internal contamination (inhalation, ingestion)
• ARS: results from whole-body exposure
• Cutaneous syndrome (CS)
  • Damage to stem cells
  • Resembles thermal burns but with a prolonged latency
  • Dry or moist desquamation

Risk Factors

• Extremes of age; men more sensitive than women
• Patients who are debilitated are more susceptible than those who are healthy.
• Natural residence in certain geographic regions
• Occupational: medical professionals, nuclear power workers, industrial radiodiagnostic workers

General Prevention

• Avoidance of exposure: exposure reduced by decreasing time, increasing distance, and shielding
• Pretreatment: In certain situations, damage to the thyroid may be reduced by preexposure consumption of radiostable iodine.