Acute Radiation Syndrome

Acute Radiation Syndrome (ARS), also known as radiation sickness, is a severe illness that occurs following exposure to high doses of ionizing radiation over a short period. It is characterized by multisystem involvement and can result in significant morbidity and mortality if not properly managed. ARS is of particular concern in nuclear accidents, radiation therapy overdoses, and nuclear warfare scenarios.

Etiology and Causes

ARS results from high-dose exposure (>1 Gy) to ionizing radiation. The main sources include:

• Nuclear accidents (e.g. Chernobyl, Fukushima)

• Nuclear explosions (e.g. Atomic bomb detonations, e.g. Hiroshima and Nagasaki)

• Radiation therapy mishaps (e.g.  Accidental overexposure in Cancer treatment/ Research)

• Occupational exposure (e.g. Industrial accidents)

Pathophysiology

Ionizing radiation primarily harms biological tissues by creating free radicals and directly damaging DNA. The level of damage is influenced by the radiation dose, dose rate, type of radiation, and the sensitivity of the tissue.

Radiation Dose Classification:

• Mild exposure (1-2 Gy): Minimal symptoms, potential hematopoietic suppression.

• Moderate exposure (2-6 Gy): Hematopoietic syndrome.

• Severe exposure (6-10 Gy): Gastrointestinal (GI) syndrome, Neurovascular syndrome

• Very high exposure (>10 Gy):  Often fatal within hours to days.

Phases of ARS:

1. Prodromal Phase (Minutes to Hours): Nausea, vomiting, anorexia, fatigue, fever.

2. Latent Phase (Hours to Weeks): Temporary symptom resolution, ongoing cellular damage.

3. Manifest Illness Phase: Development of major syndromes:

   • Hematopoietic Syndrome (1-6 Gy): Bone marrow suppression, pancytopenia, hemorrhage, infections.

   • Gastrointestinal Syndrome (6-10 Gy): Mucosal damage, severe diarrhea, dehydration, electrolyte imbalance.

   • Neurovascular Syndrome (>10 Gy): Seizures, ataxia, altered mental status, cardiovascular collapse.

4. Recovery or Death: Recovery in weeks to months for mild cases; severe cases lead to multi-organ failure and death.

Clinical Features and Diagnosis

Diagnosis is based on history, clinical presentation, and laboratory findings:

• History of radiation exposure (dosimetry if available)

• Early symptoms (nausea, vomiting, diarrhea)

• Lymphocyte depletion kinetics (absolute lymphocyte count < 500/μL within 48 hours suggests severe exposure)

• Cytogenetic analysis (chromosomal aberrations in lymphocytes)

• Biomarkers of radiation exposure (e.g., Flt3 ligand)

Management

Management of ARS is largely supportive and depends on the severity of exposure.

General Supportive Care:

• Fluid and electrolyte management (for dehydration and shock)

• Nutritional support (to counteract catabolic state)

• Pain management and symptomatic relief

Specific Therapies:

1. Hematopoietic Support (For Doses 2-6 Gy):

   • Hematopoietic growth factors (G-CSF, GM-CSF) to stimulate bone marrow recovery.

   • Stem cell transplantation in severe bone marrow suppression.

   • Broad-spectrum antibiotics to prevent secondary infections.

2. Gastrointestinal Management (For Doses 6-10 Gy):

   • Anti-emetics and anti-diarrheal (ondansetron, loperamide).

   • Parenteral nutrition if severe GI involvement.

   • Fluid and electrolyte replacement.

3. Neurovascular Syndrome (For Doses >10 Gy):

   • Palliative care (as survival is unlikely).

   • Seizure control and sedation.

4. Radioprotective Agents:

   • Potassium iodide (KI): To block radioactive iodine uptake by the thyroid.

   • Prussian blue: For cesium and thallium exposure.

   • DTPA (Diethylenetriamine pentaacetate): For plutonium, americium, and curium contamination.

   • EDTA

5. Psychological and Long-Term Follow-up:

   • Counseling and mental health support.

   • Regular monitoring for delayed effects like cancers and organ dysfunction.

Prognosis

Prognosis depends on radiation dose, promptness of treatment, and individual susceptibility. Lethal doses (LD50) without medical intervention is approximately 3-4 Gy, while aggressive supportive care can improve survival at higher doses.

Conclusion

ARS is a life-threatening condition that requires rapid assessment and intensive management. Understanding the dose-dependent effects, early recognition of clinical phases, and implementation of appropriate supportive and specific interventions are crucial in improving outcomes. Medical professionals, particularly in emergency and disaster medicine, must be well-equipped to handle radiation emergencies efficiently.