Filtration increases beam quality by removing low-energy photons. What is the main patient-dose effect of this filtration?

• A. Reduces patient dose by removing low-energy photons.
• B. Increases skin dose.
• C. Has no effect on dose.
• D. Increases scatter.

Answer: (A)

Hardening the beam by filtration removes the very low-energy photons that would deposit most of their energy in the superficial tissues of the patient. Those photons contribute heavily to entrance skin dose but do not improve image formation. By filtering them out, the energy delivered to the skin is reduced, so the entrance dose decreases. The photons that remain are higher energy and penetrate more, but for a given exposure this filtration lowers the overall patient dose. The other options don’t fit because filtration does not increase skin dose, has a clear dose effect, and does not primarily raise scatter.