Acute Radiation Syndrome

Aka: Acute Radiation Syndrome, Radiation Syndrome, Radiation Exposure, Radiation Poisoning, Radiation Sickness, Radiation Toxicity, Radiation Injury, Ioninzing Radiation Injury, Radiation Sickness Syndrome, Radiation-Induced Disorder

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II. Epidemiology

  1. Civilian Radiation Exposure is rare
    1. https://en.wikipedia.org/wiki/List_of_civilian_radiation_accidents
  2. Radioation Exposures are typically limited to industrial accidents, terrorist attacks and war zones
    1. https://en.wikipedia.org/wiki/Lists_of_nuclear_disasters_and_radioactive_incidents

III. Definitions

  1. Radiation
    1. Energy transmitted from a source through space or objects
  2. Ionizing Radiation
    1. Electromagnetic waves or subatomic particles with energy levels capable of removing electrons from atoms
    2. Examples include higher energy forms of UV light, gamma rays and xrays
    3. Nuclear materials emit ionizing radiation
  3. Non-ionizing Radiation
    1. Lower energy sources that do not cause ionization of atoms (loss of electrons)
    2. Examples include visible light, laser, infrared light, microwaves, radio waves and low level UV light
  4. Acute Radiation Syndrome
    1. Radiation Exposure resulting in severe, specific organ injury with risk of death within hours to months
  5. Radiation-Induced Multiorgan Failure
    1. Progressive dysfunction of 2 or more organ systems over time as a result of ionizing Radiation Exposure
  6. Radiation Combined Injury
    1. Radiation Injury AND blunt Trauma, Penetrating Trauma, Burn Injury, Blast Injury or infection

IV. Pathophysiology

  1. Body tissues with high cell turnover (high mitotic index) are most susceptible to ionizing radiation
    1. Bone Marrow
    2. Gastrointestinal Tract
    3. Skin
  2. Radiation particle type dictates the cell targets and degree of injury
    1. Alpha Particles (e.g. Radon Gas)
      1. Composed of 2 protons and 2 neutrons, with low penetration (blocked by clothing)
      2. Injury is by inhalation with alveolar injury or ingestion with intestinal mucosa injury
      3. Associated with secondary cancer development
    2. Beta Particles (e.g. nuclear power plants, medical nulcear material)
      1. Composed of electrons, with higher penetration than alpha particles (but will not penetrate clothing)
      2. Risk of Skin Injury, ingestion and Inhalation Injury
    3. Gamma Rays (e.g. nuclear explosion)
      1. Mass-Less, high energy electromagnetic radiation rays with high penetration
  3. Radioactive material exposure types
    1. As of 2025, no U.S. clinician has been harmed caring for patients with radiation contamination or exposure
    2. Direct exposure (e.g. nuclear explosion)
      1. Close proximity to radiation source
      2. Patient's removed from radiation source do not expose others (i.e. emit radiation)
    3. Contamination (e.g. ingestion of contaminated food or water)
      1. Patient contains radioactive material on their skin and clothing (e.g. dust), or inhaled or ingested
      2. Contaminated patients can still emit radiation and expose other before Decontamination
        1. Initiate Decontamination procedures
  4. Sources
    1. External Radiation Exposure (most common)
      1. Source is outside the human body (no continued exposure after removal from external source)
      2. See risk factors below
    2. Internal Radiation Exposure (rare)
      1. Patient is exposed via radiation ingestion, inhalation, injection or absorption
      2. Patient remains contaminated with continued Radiation Exposure to themselves and others
  5. Radiation Exposure levels correlate with effects and mortality
    1. Dose reflects whole body or significant partial body Radiation Exposure
      1. Gray (Gy) is the the preferred, SI measurement unit of absorbed radiation
      2. Rad is the radiation measurement unit used in the United States
        1. One Gray is equivalent to 100 rads
    2. Dose >1 Gy
      1. Threshold for Acute Radiation Syndrome
    3. Dose >2 to 3 Gy
      1. Hematopoietic Syndrome
    4. Dose 3.5 to 4 Gy
      1. Lethal Dose in 50% of patients within 60 days (LD50/60) without supportive care
      2. With general supportive care LD50/60 increases to 4.5 to 7 Gy
      3. With rapid Intensive Care, reverse isolation, Bone Marrow TransplantLD50/60 increases to 7 to 9 Gy
      4. Radiation Exposures >=10 Gy are nearly 100% lethal regardless of treatment
    5. Dose >5 to 12 Gy
      1. Gastrointestinal Syndrome
    6. Dose >10 to 12 Gy
      1. Uniformly lethal dose
    7. Dose >10 to 20 Gy
      1. Cerebrovascular Syndrome

V. Risk Factors

  1. High risk exposures
    1. Nuclear power reactor exposure
    2. Industrial or research facility exposure
    3. Nuclear weapons
  2. Overexposure
    1. Medical exposures were responsible for 60% of all radiation accidents and overexposures, 1980-2013
      1. Coeytaux (2015) PLoS One 10(3): e0118709 [PubMed]
    2. Medical intervention providers
      1. Interventional cardiology
      2. Interventional Radiology
    3. Sealed source radiation (higher radiation activity if accidental release)
      1. Nuclear imaging using technetium-99m
      2. Thyroid uptake with Iodine-123
    4. Unsealed source radiation (lower radiation activity)
      1. Stress Imaging using thalium-201
      2. Radio-Iodine-131 for Thyroid ablation)
  3. Other exposures
    1. Radioactive material transport
    2. Radioactive waste management

VI. HIstory

  1. Location of exposure in relation to radiation source
  2. Injuries related to exposure (including burn injuries)
  3. Dose of exposure
    1. High dose rate (high dose over short period) is associated with increased injury
    2. Dose rate decreases by the square of the distance from the source
    3. Shielding reduces exposure

VII. Findings: Acute Radiation Syndrome

  1. Prodromal Phase (0 to 2 days after exposure)
    1. Symptoms reflect severity of exposure
      1. Lower dose exposures (<1 Gy) may be associated with mild or absent symptoms
      2. Significant, potentially lethal exposures (>2 Gy) are associated wih symptoms in the first 2 hours
      3. Highly lethal doses (>10 to 20 Gy) are associated with symptom onset within minutes of exposure
    2. Anorexia
    3. Nausea
    4. Vomiting
    5. Diarrhea
    6. Fever
    7. Tachycardia
    8. Headache
    9. Apathy
  2. Latent Phase (2 to 20 days after exposure)
    1. Symptoms temporarily abate during latent phase
    2. In high Radiation Exposures, latent phase may only last hours
  3. Manifest Illness (21 to 60 days after exposure)
    1. Severe, often life-threatening effects of organ dysfunction
    2. Findings specific to the associated hematopoietic, GI and CNS syndromes (see below)
  4. Recovery Phase
    1. Radiation Exposure 2 to 6 Gy
      1. Recovery over weeks to months
    2. Radiation Exposure 6 to 8 Gy
      1. Recovery over months to years

VIII. Findings: Associated Syndromes

  1. Cutaneous Syndrome
    1. See Burn Injury
    2. Considered separately from the primary Radiation Syndromes (hematopoietic, GI and CNS)
      1. Cutaneous Radiation Injury (isolated without other syndrome involvement)
      2. Cutaneous Radiation Syndrome (combined with hematopoietic, GI or CNS syndromes)
    3. Prodromal findings (within 1-2 days)
      1. Skin erythema and edema (capillary dilation)
      2. Bullae
    4. Latent Phase
      1. Duration 1 to 5 weeks (shorter in high dose cutaneous exposures)
    5. Manifest Illness
      1. Cutaneous Radiation Injury (<2 Gy)
        1. Full effects may be delayed years
      2. Cutaneous Radiation Syndrome (higher skin exposures >20-40 Gy)
        1. Desquamation (dry or moist)
        2. Skin Ulceration (may affect deep tissue down to Muscle or bone)
        3. Onycholysis
  2. Hematopoietic Syndrome (Dose >0.7 Gy, and esp. >2 to 3 Gy)
    1. Prodromal Findings
      1. Lymphopenia (see labs above)
        1. Earliest affected cell line after Radiation Exposure
        2. See labs below
      2. Neutropenia and Thrombocytopenia nadir at 2 to 4 weeks, but may persist months
      3. Anemia (also compounded by gastrointestinal Hemorrhage)
    2. Latent Phase
      1. Typically asymptomatic, while Bone Marrow cells die
    3. Manifest Findings (over weeks to months)
      1. Bone Marrow aplasia or hypoplasia
      2. Pancytopenia
      3. Immunocompromised
      4. Poor Wound Healing
      5. Increased bleeding risk
  3. Gastrointestinal Syndrome (Dose >5 to 12 Gy)
    1. Onset within 5 days of exposure
    2. Mild GI symptoms (Nausea, Vomiting) are seen at low dose exposures (<1.5 Gy) in prodromal phase
    3. High dose exposures (>5 Gy) are associated with loss of intestinal crypt cells and mucosal barrier
      1. Associated with more severe Abdominal Pain and Diarrhea, with subsequent Gastrointestinal Bleeding
      2. Management includes fluid and Electrolyte replacement, and in some cases Total Parenteral Nutrition
    4. Prodromal Findings
      1. Crampy Abdominal Pain
      2. Diarrhea
      3. Nausea and Vomiting
      4. Gastrointestinal Bleeding
    5. Manifest Findings (typically after day 7)
      1. Vomiting
      2. Severe Diarrhea
      3. Malnutrition
      4. High fever (suggests Bacterial gut translocation)
      5. Sepsis
      6. Bowel wall necrosis, perforation, ileus
  4. Cerebrovascular Syndrome (Dose >10 to 20 Gy)
    1. Associated with capillary injury at blood brain barrier, Cerebral edema and Meningitis
    2. Onset within minutes to hours of exposure, and minimal prodromal and latent phases
    3. Most patients die within 3 days of symptom onset (survival is rare)
    4. Manifest Findings
      1. Severe Nausea and Vomiting
      2. Headache
      3. Altered Mental Status
      4. Seizures
      5. Ataxia
      6. Decreased Deep Tendon Reflexes
      7. Generalized intracranial edema (on CT or MRI)

IX. Labs

  1. See Unknown Ingestion
  2. Mouth and nasal swabs for radiation testing
  3. ABO Type and Screen
    1. Obtain specific HLA testing before transfusion of any blood or Platelets
  4. Complete Blood Count (CBC) with differential
    1. Repeat CBC every 6 to 12 hours for first 3 days
    2. Observe for decreased White Blood Cells (esp. Absolute Lymphocyte Count)
      1. Absolute Lymphocyte Count depletion course best predicts exposure and prognosis
        1. Lymphocyte Count decreases first after Radiation Exposure
      2. Absolute Lymphocyte Count >50% of normal at 48 hours after exposure is reassuring
        1. Associated with >90% survival
        2. Predicts Radiation Exposure <1 Gy
      3. Lymphocyte Count >1000 is associated with a better prognosis
        1. Lymphocyte Count maintained at 50% of normal in first week suggests <1 Gy exposure
      4. Lymphocyte Count <500 is associated with very poor prognosis (highly lethal if <100)
        1. High dose exposure (>5 Gy): 50% Lymphocyte drop in 24 hours, and more severe drop in 48 hours
  5. Other daily labs for first 3 days
    1. Serum Electrolytes
    2. C-Reactive Protein
    3. Serum Amylase
      1. Marker of parotid gland Radiation Exposure

X. Management: Hospital Arrival and Decontamination

  1. General
    1. See Mass Casualty Incident
    2. Consult radiation and nuclear exposure experts
  2. Staff should use appropriate Personal Protective Equipment (PPE)
    1. No special radiation suit exists
    2. Masks (N95 Mask, PAPR or CAPR)
    3. Droplet precautions (gowns or jumpsuits and gloves)
      1. Water-resistant clothing
      2. Caps
      3. Shoe covers
      4. Protective eye wear
    4. Double glove
      1. Inner glove set (closest to skin) is taped to clothing
      2. Outer glove set is changed frequently
    5. Personal Radiation dosimeter (if available)
      1. Worn under protective clothing
  3. Decontamination
    1. Life saving interventions (e.g. ABC Management, acute Hemorrhage Management) take priority over Decontamination
      1. Externally irradiated patients are not an exposure risk to care givers
      2. Decontamination may continue as life threatening presentations stabilize
    2. Create two zones
      1. Clean Zone
        1. Patients cross a well demarcated line or roped area AFTER Decontamination
      2. Dirty Zone (e.g. in Ambulance bay)
        1. Cover the walls and floor with protective tarp
        2. Staff working in dirty area should wear full PPE (see above)
    3. Measures
      1. Remove all clothing (removes 70-90% of contaminants)
        1. Dispose in bags marked as hazardous waste
      2. Full body examination
        1. Examine all skin for shrapnel
        2. Examine skin for residual radioactive material
          1. Remove radiaoactive material with forceps and place in lead container
          2. Consult surgery before removal if material is embedded in vital structures
      3. Wash skin
        1. See Skin Decontamination
        2. Use soap and warm water, mild detergent or 3% Hydrogen Peroxide
        3. Irrigate eyes, ears, nose and pharynx with Isotonic Saline
        4. Avoid heavy scrubbing of skin (risk of skin breakdown and contamination)
      4. Consider chelating agents (e.g. DTPA, Prusssian Blue, Calcium Phosphate, aluminum phosphate)
        1. Decontamination agents are available for specific exposures (e.g. Uranium: 1.4% bicarbonate solution)
        2. Expert Consultation (e.g. poison control) is recommended
      5. Test for residual radiation with Geiger Counter
        1. Geiger counter may be obtained from emergency personnel (e.g. fire department)
        2. Evaluate baseline and after Decontamination
          1. Repeat Decontamination cycle if residual material
          2. Monitor dirty zone environment for radiation levels
          3. Continue Decontamination until radiation <2x baseline radiation levels
          4. Stop after 2 cycles, if radiation does not drop by >=10% between cycles
    4. Staff Safety
      1. Radiation Exposures are typically insignificant to staff performing Decontamination of residual material
      2. Staff Radiation Exposure is similar to normal background environmental Radiation Exposure
  4. Triage and Scoring of patients
    1. European Medical Treatment Protocols for Radiation Accident Victims (METREPOL)
      1. Clinical and laboratory triage system more appropriate for small incidents
    2. Radiation Injury Treatment Network (RITN)
      1. Mass Casualty Incident level scoring (includes computer modeling)
    3. Other Trauma triage scales
      1. Trauma Triage in the Field
      2. Pediatric Trauma Score
      3. JumpSTART Triage
      4. SALT Triage
      5. START Triage
  5. Other evaluation
    1. See Primary Trauma Survey
    2. See Secondary Trauma Survey
    3. ABC Management

XI. Management: Other Measures

  1. Basic Supportive Care
    1. Intravenous Fluids
      1. Avoid over-Resuscitation (fluid needs are less than in severe Burn Injury)
    2. Electrolyte replacement
    3. Anti-emetics (e.g. Ondansetron)
    4. Total Parenteral Nutrition may be needed in severe gastrointestinal syndrome
    5. Analgesics
      1. NSAIDs
      2. Acetaminophen
      3. Opioids for refractory pain
    6. Maintain gastric acidity (avoid Proton Pump Inhibitors and H2 Blockers)
      1. May use Sucralfate for Stress Ulcer prevention
    7. Platelet Transfusion indications
      1. Platelet Count <20,000 (or <75,000 if perioperative)
  2. Treat specific injuries
    1. See Burn Management
    2. See Blast Injury
    3. See Penetrating Trauma
    4. See Smoke Inhalation Injury
    5. See Acute Poisoning
  3. Patient Triage to 4 categories
    1. Response Categories (RC) are based on triage system used (e.g METREPOL)
    2. Recovery is expected with minimal supportive care (<1 Gy exposure, RC1)
      1. No Vomiting in first 3 hours or skin erythema within 24 hours
      2. Employ basic measures as above
      3. Outpatient follow-up with complete system review daily for 6 days
      4. Follow-up at 1 week after exposure
    3. Moderate Radiation Injury (RC2, 1-2 Gy Exposure)
      1. Vomiting at 2-3 hours after exposure or skin erythema within 24 hours
      2. Full system reevaluation every 12 hours until stable
      3. General medical-surgical unit is typically appropriate
    4. Severe Radiation Injury but survival is possible with aggressive supportive care (RC3, >2 Gy Exposure)
      1. Vomitin within first 2 hours after exposure
      2. Triage to Intensive Care
      3. Reevaluate every 6 hours until stable and then every 12 hours for up to 6 days
      4. Consult hematology, burn specialists
      5. Reverse Isolation (>2 to 3 Gy exposure)
    5. Expected to succumb (RC4, >10 Gy exposure, concurrent injuries or inadequate resources)
      1. Triage to Palliative Care
      2. Reevaluate every 6 hours for the first 3 days
  4. Hematopoietic Syndrome with myelosuppression (e.g. Pancytopenia)
    1. Administer Granulocyte Colony Stimulating Factor (or similar) early
    2. Perform any emergent surgeries in first 48 hours (cell counts are expected to drop after this)
  5. Thyroid Cancer Risk
    1. Risk of Radioactive Iodine uptake in children and pregnant women
    2. Give as early as possible (<4 hours is preferred, and ineffective at >12 hours after exposure)
    3. Give prophylactic Potassium Iodide to patients at risk as early as possible
      1. Adult: 130 mg orally daily
      2. Child (over age 3 years old): 65 mg orally daily
      3. Infant (one month to age 3 years): 32 mg
  6. Infection Risk
    1. Perform any urgent or emergent surgery in first 24 to 36 hours
    2. Treat infections early
    3. Irradiate blood components prior to transfusion
    4. Consider prophylactic Antibiotics in Neutropenia
    5. Evaluate for CMV risk
    6. Evaluate for Pneumocystitis carinii risk (CD4 <200/ul)
  7. Cutaneous Radiation Syndrome
    1. Consult burn specialists
    2. May apply Linoleic Acid cream
    3. Consider Betamethasone cream to decrease inflammation
    4. Consider Pentoxifylline to prevent radiation fibrosis (decreases blood viscosity and increases Blood Flow)
  8. Internal Radiation Contamination (e.g. Ingestion, Inhalation)
    1. Consult radiation and hematology specialists
    2. Consider systemic chelating agents

XII. Resources

  1. Radiation Emergency Assistance Center/Training Site (REAC/TS, Oak Ridge Institute)
    1. https://orise.orau.gov/reacts/index.html
    2. REAC/TS offers emergency Consultation regarding the care of radiation exposed patients
    3. On call (24/7) assistance from nurse, physician and physicist
  2. TMT Handbook (Rojas-Palma, 2009)
    1. https://remm.hhs.gov/tmt-handbook-20091.pdf
    2. Triage, monitoring and treatment of people exposed to the malevolent use of inonizing radiation

XIII. References

  1. Vasisht and Falat (2025) Crit Dec Emerg Med 39(11): 4-13
  2. Acosta and Warrington (2022) Radiation Syndrome, Stat Pearls, Treasure Island, accessed 5/11/2022
  3. Studer and Swaminathan (2025) EM:Rap, 2/3/2025
  4. López (2011) Rep Pract Oncol Radiother 16(4):138-46 +PMID: 24376971 [PubMed]

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