A patient receives an entrance skin dose of 5 mGy during a lumbar spine procedure. How much exposure will the radiographer receive when standing 1 meter from the patient?

• A. 0.025 mGy.
• B. 0.015 mGy.
• C. 0.005 mGy.
• D. 0.01 mGy.

Answer: (C)

Scatter radiation from the patient is what the radiographer receives, and its intensity drops off quickly with distance. In this kind of problem, the exposure at about one meter from the patient is roughly one thousandth of the entrance-skin dose at the patient. So, taking the patient’s entrance skin dose of 5 mGy and multiplying by 0.001 gives 0.005 mGy for the radiographer’s exposure at one meter.

This reflects the inverse-square behavior of radiation and the additional geometry/attenuation factors that reduce scatter reaching the radiographer. If you stood closer, exposure would increase (roughly with the square of the distance change); if you stood farther away, it would decrease accordingly.