Which factors contribute to nonuniform radiation dose distribution within the body?

• A. Restriction of the primary beam
• B. Restriction of the primary beam and shielding of body parts
• C. Internal scattering of the beam
• D. Shielding of body parts

Answer: (B)

Nonuniform dose distribution happens because the energy delivered to the body is not spread evenly. When the beam is restricted, only a specific region receives direct photons, so tissues within that field get a higher dose while nearby tissues outside the field receive little or no direct exposure. Shielding body parts further reduces dose to those areas, creating a sharp difference between shielded and unshielded tissues. Internal scattering does contribute some energy to surrounding tissues, but the main drivers of pronounced nonuniformity are limiting the beam and shielding parts of the body.