Safety
Core concepts
Safety questions blend radiation protection with general workplace safety. The organizing principle is ALARA, achieved through time, distance, and shielding. Understand the inverse square law and be able to compute exposure at a new distance. Know the occupational dose limits (effective dose, lens of eye, extremities/skin), the lower limits for the general public and for a declared pregnant worker, and the concept of the dose limit is not a threshold for acceptable exposure. Know area signage, barriers, interlocks, emergency-off buttons, machine and room survey procedures, badge programs (TLD/OSL), and the requirement to survey after any source or patient procedure involving radioactivity.
Non-radiation safety matters too: patient identification with two identifiers, falls precautions, side-rail and bed-height checks, oxygen safety, electrical safety, latex allergy, hazardous-drug handling, and emergency response (fire, code, power failure, source stuck in brachytherapy).
Traps
- Mixing units: 1 mSv = 100 mrem. Dose-limit questions are usually unit-conversion questions.
- Applying public limits to occupationally exposed workers, or forgetting the lens and extremity limits differ from whole-body.
- Forgetting that the patient's own exposure is not subject to a dose limit - only justified and optimized.
- Assuming a door interlock resets itself after a beam interruption.
Worked example / rule of thumb
A source reads 80 mR/hr at 1 m. At 4 m: exposure falls by the square of the distance ratio, 80 × (1/4)² = 5 mR/hr. Doubling distance quarters exposure; tripling it reduces exposure to one-ninth. When in doubt, increase distance first - it is free and immediate.