A. Types of Radiation Injury

1. External irradiation
2. External contamination with radioactive materials
3. Internal contamination by inhalation, ingestion, transdermal absorption
4. May occur as combinations of above
5. May be associated with thermal burns, traumatic injuries

B. Major Organs Affected

1. Rapidly dividing cells are most affected
2. Bone marrow derived cells are most sensitive
   1. Lymphopenia occurs before other cells affected
   2. Reduction of lymphocyte counts >50% in first 24 hours characterizes potential lethality
   3. Burns and trauma contribute to lymphopenia
3. Spermatocytes also very sensitive
4. Gastrointestinal (GI) Mucosa
   1. Loss of intestinal crypts and breakdown of mucosal barrier (mucositis)
   2. Abdominal pain, diarrhea, nausea and vomiting
   3. Predisposition to infection
   4. Dehydration and/or malnutrition from malabsorption
   5. Bowel obstruction from ileus
5. Cutaneous Syndrome
   1. Cutaneous injury from thermal or radiation burns
   2. Loss of epidermis, possibly dermis
   3. Damage my penetrate into underlying muscle and even bone
   4. Profound local edema and loss of fluids
   5. Thermal burns occur rapidly; radiation burns require longer
6. Prodromal phase usually within 48 hours, but up to 6 days after exposure

C. Radiation Effects with Dose (Table 1, Ref [1])

1. 0.5-1.0 Gy
   1. Mild with slight decrease in blood cell counts
   2. Survival near 100%
2. 1.0-2.0 Gy
   1. Mild to moderate with early signs of bone marrow damage
   2. >90% survival
3. 2.0-3.5 Gy
   1. Moderate to severe bone marrow damage
   2. Probable survival without therapy
   3. Expect survival with bone marrow support, infection control
4. 3.5-5.5 Gy
   1. Severe bone marrow damage with slight GI damage
   2. 50% mortality <6 weeks without therapy
5. 5.5-7.5 Gy
   1. Pancytopenia and moderate GI damage
   2. Death probable within 3 weeks without therapy
6. 7.5-10 Gy
   1. Marked GI and bone marrow damage, hypotension
   2. Death probable within 2.5 weeks without therapy
7. 10-20 Gy
   1. Severe GI damage, pneumonitis, altered mental status, cognitive dysfunction
   2. Death certain within 5-12 days (>12 Gy death certain even with treatment)
8. 20-30 Gy
   1. Severe cerebrovascular collapse, fever, shock
   2. Death certain within 2-5 days

D. Overview of Treatment Modalities

1. Hematopoietic Syndrome
   1. Short-term therapy with cytokines for exposure <3 Gy
   2. Prolonged cytokine, transfusion, possibly transplantation for >7 Gy exposure
   3. Main cytokines are GM_CSF, G-CSF, and pegylated G-CSF
2. Infection Prophylaxis
   1. Primarily with absolute neutrophil counts (ANC) <500/µL
   2. Broad spectrum antimicrobial such as anti-streptococcal fluoroquinolone
   3. Antiviral drugs such as valacyclovir, acyclovir, famciclovir
   4. Antifungal agent such as fluconazole
3. Gastrointestinal Symptoms
   1. Supportive care for exposure to <12 Gy
   2. Fluid replacement
   3. Prophylaxis against initial episode of vomiting not recommended (prognostic value)
   4. Vomiting usually abates within 72 hours at low exposures
   5. May treat vomiting after initial episode
   6. Prophylaxis against ulceration in the GI tract
   7. Anti-diarrheal agents reduce loss of fluids from GI tract
   8. Avoid instrumentation of GI tract since mucosa is highly friable after radiation exposure
4. Pain Control
   1. Narcotics generally required
   2. Non-steroidal antiinflammatory drugs (NSAIDs) avoided due to GI and renal toxicities

References

1. Waselenko JK, MacVittie TJ, Blakely WF, et al. 2004. Ann Intern Med. 140(12):1037