Radiation Safety

Ionising radiation is:

• Used regularly for diagnosis and intervention
• Harmful
  Significant statutory regulations exist to reduce this harm. Exposure should be:
  • As Low as Reasonably Practicable
  • Justified

Radiobiology

Ionising radiation:

• Consists of charged particles that transfer energy to a medium they pass through
  Known as linear energy transfer, measured in kiloelectrovolts/micrometer.
  • X-rays and gamma radiation is relatively low LET
  • α-particles and neutrons are high LET
• Dosage is quantified using two SI units
  • Gray (Gy)
    Absorption of 1J/1kg of matter.
  • Sievert (Sv)
    Derived unit of dose-equivalent radiation, for x-rays Sv is identical to Gy.
• Mechanism of injury is direct or indirect:
  • Direct
    Predominant mechanism of high LET.
    • Direct ionisation of atoms or molecules, leading to biological damage
  • Indirect
    • Predominant mechanism of low LET
    • Energy displaces electrons from water molecules and generates free radicals
      
    • Free radicals lead to DNA disruption
      
• Damage is classified by two methods:
  • Somatic or genetic
    • Somatic
      Effect on the individual. May be:
      • Acute
        
        • Present usually in hours-days
        • Short duration of high exposure
        • Clinical effect depends on the dose
          • High dose causes cell death
          • Lower doses cause damage that is either repaired or contributes to carcinogenesis
      • Chronic
        • Present usually in months-years
        • Clinical effects include:
          • Chronic inflammation
            Fibrosis, atrophy, ulceration.
          • Cancer
            Most commonly AML, CML, and skin, bone, lung, thyroid, and breast cancers.
    • Genetic
      Effect on offspring, via mutations passed on via gametes.
  • Deterministic or stochastic
    • Deterministic
      Dose-dependent manifestation.
    • Stochastic
      Magnitude of effect is independent of dose, though likelihood ↑ with ↑ dose.
      • e.g. Carcinogenesis

Radiation Safety

Principles:

• Ensure exposure is justified:
  • Objective of exposure
  • Total potential diagnostic and therapeutic benefit
  • Harm of exposure
  • Risk-benefit of technique
• Use appropriate imaging technique
  • Lowest exposure possible
  • Pulsed rather than continuous screening
  • Move source close to object as possible
  • Use laser to accurately position II prior to exposure
  • Use beam collimation
    Reduces size and divergence of beam; improving image quality and reducing exposure area.
• Minimise exposure
  • Restrict presence of staff and other persons
  • Provide PPE
    Ensure proper use, application, and storage.
• Pregnancy and breastfeeding
  • Prevent >1mSv dose to foetus
  • Prevent bodily contamination for breastfeeding employees
  • Pregnant employees notify employer

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References

1. Taylor J, Chandramohan M, Simpson KH. Radiation safety for anaesthetists. Contin Educ Anaesth Crit Care Pain. 2013 Apr 1;13(2):59–62.