RD3.{1,3} | Radiation Types, Biological Hazards and Dose Awareness — Summary & Reflection

KEY TAKEAWAYS

Radiation Types, Hazards, Units and Monitoring — Key Points

• Ionising radiation in imaging = X-rays (radiography, fluoroscopy, angiography, CT) and gamma rays (nuclear medicine). Non-ionising = ultrasound and MRI (preferred when diagnostically adequate, especially in pregnancy/children).
• Ionising radiation harms tissue in two distinct ways:
• Stochastic — NO threshold, dose raises probability, late onset: carcinogenesis and hereditary effects. Basis of the linear-no-threshold model.
• Deterministic (= non-stochastic / tissue reaction) — HAS a threshold, dose raises severity, early onset: skin erythema, epilation, cataract, sterility, acute radiation syndrome.
• Mechanism: ionisation → DNA damage by direct action and, predominantly for diagnostic X-/gamma rays, indirect action (water radiolysis → free radicals). A few surviving mutated cells → stochastic (late); mass cell death above threshold → deterministic (early).
• Units: absorbed dose = Gray (Gy) (physical energy); equivalent and effective dose = Sievert (Sv) (biologically weighted risk). Effective dose (mSv) compares examination risk. Gray = physics in; Sievert = risk out.
• Dose scale: CXR ~0.02 mSv; CT abdomen–pelvis ~8–10 mSv (~400–500× a CXR); USG/MRI = no ionising dose.
• Monitoring: personal dosimeter — primarily the thermoluminescent dosimeter (TLD) (heated crystal emits light ∝ dose); also film badge, pocket dosimeter, OSL. A high reading in a well worker = a stochastic-risk flag to review practice, not an acute illness.
• Special populations: fetus and children are more radiosensitive → heightened justification and optimisation.

REFLECT

Think back to the last imaging request you saw ordered on a ward round. Ask yourself: (1) Was it an ionising study (X-ray/CT/nuclear) or non-ionising (USG/MRI) — and could a non-ionising option have answered the same question? (2) Roughly what effective dose, in mSv, did it deliver, and how does that compare with a chest X-ray or a year of background radiation? (3) If a radiation worker in that room had an unexpectedly high dosimeter reading, would you now correctly recognise that as a stochastic-risk signal to review technique rather than a sign of acute illness? Carrying these three questions into your clinical work is how dose awareness becomes a habit rather than a fact.