If a patient’s entrance skin dose during a lumbar spine exam is 5 mGy, what approximate radiographer exposure at 1 meter distance?

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

Answer: (C)

The main idea is that the radiographer’s exposure at 1 meter mainly comes from scatter radiation off the patient, not the primary beam. Scatter at a distance of about 1 meter from the patient is typically only a tiny fraction of the patient’s entrance dose—roughly around 0.1% (0.001) in many lumbar spine exams.

So, estimate the radiographer’s exposure by multiplying the patient dose by this scatter factor: 5 mGy × 0.001 ≈ 0.005 mGy. This is a reasonable approximation, recognizing that exact values depend on factors like field size, kVp, shielding, and technique.

The other options would imply larger scatter fractions (around 0.2–0.5%), which are not typical at 1 meter for a lumbar spine study, hence the chosen value best reflects standard scatter exposure at that distance.