Radiation Health Effects

Radiation Basics - Zap & Measure

• Radiation Types (Ionizing - Ejects electrons):
  • Particulate: Alpha (α), Beta (β), Neutron (n).
  • Electromagnetic (EM): X-rays, Gamma (γ) rays.
• Penetration 📌 (Least → Most): α (paper) < β (plastic/Al) < γ/X-rays (lead).
• Sources:
  • Natural: Cosmic, terrestrial (radon, K-40).
  • Man-made: Medical (X-rays, CT), industrial, nuclear.
• Units:
  • Activity: Becquerel (Bq) (1 dps).
  • Exposure (X/γ rays in air): Roentgen (R).
  • Absorbed Dose (energy/mass): Gray (Gy) ($J/kg$)
  • Equivalent Dose (biological effect): Sievert (Sv) ($H = D \times Q$)
  • Effective Dose (overall risk): Sievert (Sv) (sum of tissue-weighted $H$)

⭐ The Sievert (Sv) is the unit of equivalent dose and effective dose, accounting for biological effectiveness of different radiation types.

Cellular Chaos - Dose & Damage

• Mechanisms of Damage:
  • Direct: Radiation directly hits & damages DNA.
  • Indirect: Radiation ionizes water $\rightarrow$ free radicals (e.g., $OH^\bullet$) $\rightarrow$ DNA damage. (Major pathway)
• Cellular Radiosensitivity (Law of Bergonie & Tribondeau): Cells are more sensitive if:
  • High mitotic rate
  • Long mitotic future
  • Undifferentiated (e.g., hematopoietic, GI lining)

⭐ The Law of Bergonie and Tribondeau states that actively dividing, undifferentiated cells with a long mitotic future are most radiosensitive.

• Deterministic Effects:
  • Threshold dose present.
  • Severity ↑ with dose (e.g., skin erythema >2 Gy, cataracts >0.5 Gy, sterility).
• Stochastic Effects:
  • No threshold (Linear No-Threshold - LNT model).
  • Probability ↑ with dose; severity independent (e.g., cancer, genetic effects).

Fallout Ills - Acute & Chronic

Acute Radiation Syndrome (ARS): Sequential phases of illness after significant radiation exposure.

, Syndrome Name, Key Features/Symptoms, Onset, and Prognosis/Survival Time)

• ARS Syndromes by Dose:

  • Hematopoietic (Bone Marrow) Syndrome (2-10 Gy): Pancytopenia (nadir 3-4 wks), infection, hemorrhage. Survival dose-dependent.
  • Gastrointestinal (GI) Syndrome (10-50 Gy): Mucosal damage (crypt cell death); nausea, vomiting, bloody diarrhea, dehydration, sepsis. Death in 3-14 days.
  • Cardiovascular (CV)/Central Nervous System (CNS) Syndrome (>50 Gy): Vasculitis, meningitis, edema; ataxia, seizures, coma. Death in <3 days.

• Chronic Effects:

  • Carcinogenesis: Leukemia (latency 5-7 yrs, excl. CML), thyroid, breast, lung, bone.
  • Heritable/Genetic Effects: Mutations (doubling dose concept).
  • Teratogenic Effects: Esp. organogenesis (8-15 wks gestation); microcephaly, intellectual disability.

⭐ The most common radiation-induced cancer is leukemia (excluding CML), with a latency period of 5-7 years.

Safety Shields - Guarding Glow

• Principles of Radiation Protection:
  • Justification: Ensure benefits outweigh risks.
  • Optimization: 📌 ALARA (As Low As Reasonably Achievable).
  • Dose Limitation: Adhere to prescribed dose limits.
• Practical Measures (📌 TDS Principle):
  • Time: Minimize exposure duration.
  • Distance: Maximize distance from source ($I \times d^2 = \text{constant}$).
  • Shielding: Use appropriate barriers (e.g., lead for X/gamma, concrete).
• Exposure Limits (AERB/ICRP):
  • Occupational: 20 mSv/year (avg. over 5 yrs).
  • Public: 1 mSv/year.
• Personal Protective Equipment (PPE): Lead aprons, thyroid shields, leaded goggles.
• Dosimetry: TLD badges for individual exposure monitoring.
• Radiation Emergencies: Decontamination, supportive care.

⭐ The ALARA (As Low As Reasonably Achievable) principle is a cornerstone of radiation protection, emphasizing optimization of safety measures.

High‑Yield Points - ⚡ Biggest Takeaways

• Deterministic effects (e.g., cataracts) have a threshold dose; severity ↑ with dose.
• Stochastic effects (e.g., cancer) have no threshold dose; probability ↑ with dose.
• Human LD50/60 (acute whole-body) is ~3.5-4.5 Gy.
• Most radiosensitive: lymphoid tissue, bone marrow, gonads.
• Most radioresistant: muscle, nerve, mature bone.
• ALARA principle guides radiation safety: As Low As Reasonably Achievable.
• Units: Gray (Gy) (absorbed dose), Sievert (Sv) (equivalent/effective dose).