Scatter radiation is radiation deflected from the patient or objects; what is its main source?

• A. Radiation that travels in straight lines without interaction.
• B. Radiation produced only by leakage from the tube.
• C. Radiation absorbed completely by the patient.
• D. Radiation deflected from the patient or objects, mainly produced by Compton interactions in the patient.

Answer: (D)

Scatter radiation comes from photons that have interacted with matter and changed direction. In diagnostic radiography, the dominant source is photons that undergo Compton scattering within the patient (and other objects in the beam). These scattered photons exit the patient at various angles with reduced energy, contributing to image fog and to occupational exposure. Primary radiation, by contrast, travels in straight lines without interaction. Tube leakage exists but is not the main source of scatter. Radiation absorbed by the patient is attenuation, not scatter. So the main source of scatter is radiation deflected from the patient or objects, mainly produced by Compton interactions in the patient.