Radiation Exposure

Radiation Basics - Tiny Rays, Big Concerns

• Ionizing Radiation: High energy; removes electrons from atoms, causing ionization.
  • Types: Alpha ($\alpha$), Beta ($\beta$), Gamma ($\gamma$), X-rays, Neutrons.
• Sources:
  • Natural: Radon (major contributor), cosmic rays, terrestrial (soil/rocks).
  • Man-made: Medical (X-rays, CT scans, radiotherapy), industrial, nuclear fallout.
• Key Units:
  • Absorbed Dose: Gray (Gy). Energy deposited/mass. (1 Gy = 100 rad).
  • Equivalent Dose: Sievert (Sv). $H = D \times W_R$ (Radiation Weighting Factor). (1 Sv = 100 rem).
  • Effective Dose: Sievert (Sv). $E = \sum_T (W_T \times H_T)$ (Tissue Weighting Factor).

⭐ Radon gas is the largest natural source of radiation exposure for the general public, contributing significantly to background radiation levels globally.

Biological Effects - Growing Bodies, Greater Risks

• Children: ↑ vulnerability due to rapid cell division, longer lifespan for effects to manifest.
• Effects:
  • Deterministic: Dose-dependent, threshold exists (e.g., skin burns, cataracts). Severity ↑ with dose.
  • Stochastic: Probability-dependent, no threshold (e.g., cancer, genetic effects). Probability ↑ with dose.
• Highly Radiosensitive Tissues: Bone marrow, thyroid, gonads, lens, developing brain, breast.
• Influencing Factors: Age (younger ↑risk), dose, dose rate, radiation type.

⭐ Children have a 2-3 times higher lifetime risk of developing radiation-induced solid cancers compared to adults exposed to the same dose.

Clinical Features - Sickness Spectrum

• Acute Radiation Syndrome (ARS): Dose-dependent, progresses through distinct phases.

• ARS Syndromes (Manifest Illness Phase):
  • Hematopoietic (Bone Marrow) Syndrome: 1-6 Gy. Lymphopenia (early indicator), pancytopenia. ↑Infection, hemorrhage.
  • Gastrointestinal (GI) Syndrome: 6-10 Gy. Severe N/V/D, mucosal denudation, dehydration, sepsis. Often fatal.
  • Neurovascular/CNS Syndrome: >10 Gy (often >20 Gy). Rapid onset: ataxia, seizures, coma. Uniformly fatal.
• Chronic Effects:
  • Carcinogenesis (leukemia, thyroid, solid tumors), genetic mutations, cataracts, pediatric growth retardation.

⭐ Lymphocyte count drop within 24-48 hours is a key early biological dosimeter for exposure severity.

Diagnosis & Management - Action Plan Alpha

• Triage & Decontaminate: Secure scene, ABCs. Remove clothes, wash skin. Consider internal decorporation.
• Estimate Dose (Biodosimetry): Lymphocyte kinetics (nadir at ~48h), dicentric chromosomes.
• Supportive Care: Fluids, antiemetics, infection prophylaxis if ANC < 500/µL.
• Management Flowchart:

• Specific Agents: KI (thyroid block), Prussian Blue (Cs, Tl), DTPA (transuranics), G-CSF (neutropenia).
• Follow-up: Monitor for ARS, late effects.

⭐ Absolute lymphocyte count at 48h is a key prognosticator for Acute Radiation Syndrome (ARS).

Prevention & Protection - Kid-Safe Shielding

• 📌 ALARA Principle: As Low As Reasonably Achievable.
• Core Principles:
  • ↓ Time: Minimize exposure duration.
  • ↑ Distance: Maximize distance from source.
  • Shielding: Use lead aprons, thyroid/gonadal shields.
• Pediatric Focus:
  • Always use child-sized shielding.
  • Effective immobilization to prevent repeat exposures.
  • Justify all radiologic procedures.
  • Prefer USG/MRI when possible.
• Nuclear Emergencies:
  • Potassium Iodide (KI) for thyroid gland protection.

⭐ Children have ↑ radiosensitivity (cells rapidly divide) & longer life expectancy for stochastic effects to manifest; 2-10x more sensitive than adults.

High-Yield Points - ⚡ Biggest Takeaways

• Children exhibit ↑ radiosensitivity; ALARA principle (As Low As Reasonably Achievable) is crucial in pediatric imaging.
• Deterministic effects (e.g., skin erythema, epilation) are dose-dependent with a threshold.
• Stochastic effects (e.g., malignancy, genetic changes) are probabilistic, with no threshold.
• Thyroid cancer is a significant concern post-exposure; Potassium Iodide (KI) for thyroid blocking.
• Acute Radiation Syndrome (ARS) phases: prodromal, latent, manifest illness, and recovery/death.
• Fetal radiation: highest risk during organogenesis (2-15 weeks gestation); doses < 50 mGy generally not linked to deterministic effects in utero.