In diagnostic radiology, reasons why radiation doses are not distributed uniformly throughout the body include:

• A. 1 and 2
• B. 1 and 3
• C. 2 and 3
• D. 1, 2, and 3

Answer: (B)

Radiation dose inside the body isn’t the same everywhere because the body isn’t a uniform material and the X-ray beam interacts with it differently across tissues. Different tissues have different densities and thicknesses, so the primary beam is attenuated to varying degrees; dense bone, for example, absorbs more photons than soft tissue, causing deeper or posterior regions to receive different amounts of dose than surrounding areas. In addition, scattered radiation within the body deposits energy in tissues that aren’t directly in the beam path, further distorting any uniform distribution. The combination of tissue-dependent attenuation and scatter is what creates the nonuniform dose pattern seen in diagnostic radiology, while other factors that would imply uniform exposure aren’t accurate contributors.