Radiation Protection and Safety
Radiation protection and safety tests how you apply justification, optimization, and dose limitation in a radiotherapy department. Questions often use dose limits, area classification, shielding, personal monitoring, and practical decisions about time, distance, and shielding.
Principles and limits
Justification requires benefit to outweigh risk; optimization is ALARA, considering economic and social factors; limitation applies to occupational and public exposures, not to a patient's medical exposure. ICRP occupational effective dose is 20 mSv per year averaged over five years, with no more than 50 mSv in any one year. Public effective dose is 1 mSv per year. Occupational lens limit is 20 mSv per year; public lens limit is 15 mSv per year. Skin and extremities are 500 mSv per year. A declared pregnant worker should receive no more than 1 mSv to the fetus during the remainder of pregnancy.
Areas and monitoring
Controlled areas require local rules, a radiation protection supervisor, warning signs, and restricted access. Supervised areas need appropriate demarcation. Personal dosimeters such as TLD or OSL badges estimate effective dose but are not real-time; electronic dosimeters give active alarms. Lead aprons reduce scatter but do not replace distance and time controls. Shielding design uses workload, use factor, occupancy factor, and distance.
Worked example
A controlled-area survey reads 10 µSv/h at 3 m from a source. At 6 m, inverse square gives 10×(3/6)^2=2.5 µSv/h. If a worker must remain there for 0.5 h, the estimated dose is 2.5×0.5=1.25 µSv. This is well below any limit, but ALARA still asks whether the task can be done at greater distance or shorter time. If the reading were at the barrier, the same logic would estimate dose beyond it.
Traps
Dose limits are not targets and do not apply to medically exposed patients. Do not add personal badge dose to a patient's treatment dose. A lead apron's stated lead equivalence is valid only at the specified kV and geometry. Inverse square fails for extended sources and scattered radiation. Public limits include visitors but exclude background and medical exposure. Declared pregnancy is voluntary and confidential.