Patient skin dose for CT examinations is usually on the order of which range?

• A. one to several mrems
• B. 10 to 20 rems
• C. one to several Gy/SV
• D. one to several RADS

Answer: (A)

The key idea is that the skin exposure from a properly performed CT exam is kept relatively small thanks to beam collimation, dose modulation, and the way the X-rays are delivered in short bursts over many rotations. Because of those factors, the entrance skin dose for a routine CT study falls into the low milli- to micro-sievert range when expressed in conventional units, which corresponds to about a few millirem per examination. That’s why the option describing one to several mrems fits the typical surface dose you’d expect from a CT scan. The other choices represent magnitudes or units that imply much larger skin exposures or different dose concepts (rems, rads, or Gy/Sv), which aren’t characteristic of standard CT skin dose.