Radiation Protection and Equipment Operation
Core concepts
Protection is governed by ALARA and the principles of time, distance, and shielding. Know the inverse square law: doubling distance reduces dose to one-fourth. Use collimation, pulsed fluoroscopy, low frame rates, and last-image-hold. Personnel shielding includes lead aprons (0.5 mm Pb equivalent), thyroid shields, leaded glasses, and ceiling-suspended shields. Dosimetry badges are worn at collar level outside the apron (or as facility directs).
Traps to watch
Questions test scatter vs. primary beam: the patient is the main source of scatter. Magnification increases dose. Cine uses more dose than pulsed fluoroscopy. Know that inverse square law and dose-area product (DAP) are common calculation topics. Understand equipment operation: ABC adjusts exposure, and collimation reduces scatter and improves contrast. Do not confuse occupational dose limits with patient dose.
Rule of thumb
For dose calculations, remember dose ∝ 1/distance². If distance doubles, dose quarters.
Worked example
A technologist stands 1 m from the patient and receives 4 mGy/h scatter. At 2 m, dose = 4 × (1/2)² = 1 mGy/h. Moving back cuts dose to one-quarter - a key ALARA principle.