Clover RT Safety Radiation Protection – Minimizing Patient Exposure Practice Exam

Entrance dose is the absorbed dose deposited at the skin where the X-ray beam enters. Because these skin doses are typically small, the common unit used is milligray (mGy). One gray equals one joule per kilogram, so expressing the skin dose in milligrays keeps the numbers practical for clinical reporting and dosimeter readings.

Why not the other units? Gy·cm^2 represents dose–area product, which combines dose with beam cross-sectional area to reflect overall patient dose, not the skin entrance dose. mSv is the effective dose used to estimate stochastic risk across tissues, not the immediate skin dose at the entry point. Gy is the gray, but in practice, skin entrance doses are usually in the milligray range, so mGy is the standard unit for ESD.