Which statement best describes the effect of decreasing filtration thickness on beam quality and dose?

• A. Beam quality increases; dose decreases
• B. Beam quality unchanged; dose unchanged
• C. Beam quality decreases; dose decreases
• D. Beam quality decreases; dose increases

Answer: (D)

Filtration acts to remove the low-energy photons from the X-ray beam, which hardens the beam and improves beam quality while also reducing the dose delivered to the patient by stripping out photons that would be absorbed superficially. If you decrease the filtration thickness, more of those low-energy photons slip through, so the beam becomes softer (lower average energy, beam quality decreases). At the same time, the overall photon fluence reaching the patient increases because fewer photons are being filtered out, which raises the absorbed dose, especially at the entrance skin. That combination—a softer beam and a higher dose—matches the statement that beam quality decreases while dose increases.