Radiation Protection
Core concepts
Protection content is heavily tested because it is regulatory and quantitative. Know ALARA and the three cardinal principles: time, distance, and shielding. Exposure falls with the inverse square of distance - double the distance, quarter the dose.
Occupational limits as commonly taught from NCRP guidance: effective dose 50 mSv (5 rem) per year; lens 150 mSv (15 rem) per year; extremity and skin 500 mSv (50 rem) per year. Public exposure: 1 mSv (0.1 rem) per year; embryo/fetus: 5 mSv (0.5 rem) over gestation. Limits are annual, not lifetime cumulative caps, and exclude background radiation and the worker's own medical exposure as a patient.
Protective practice: collimate to the part, use the highest kVp consistent with needed contrast while reducing mAs, avoid repeats, follow shielding policy, and stand behind a barrier during mobile exams. Never hold a patient unless it is a genuine emergency, and then wear lead and have the exposure documented.
Personnel monitoring: badges are worn at collar level outside the apron, with a second badge under the apron when dose is expected to be high. Pregnant workers may voluntarily declare pregnancy to receive dose monitoring.
Know the vocabulary: primary versus secondary (scatter and leakage) radiation; ESE, DAP, and effective dose measure different quantities. Pediatric patients carry higher risk per unit dose - reduce mAs and collimate aggressively.
Traps
- Treating the 50 mSv limit as a cumulative lifetime maximum.
- Wearing the primary badge under a lead apron.
- Assuming a lead apron eliminates all dose.
- Choosing low kVp "for safety" - it raises patient dose.
- Ignoring scatter from the patient as an operator dose source.
Rule of thumb
Distance beats shielding: step back before reaching for an apron.
Example: Moving from 1 m to 2 m from a scatter source cuts exposure to roughly 25%.