Which filtration thickness will most decrease the patient's skin dose?

• A. 1 mm
• B. 0.5 mm
• C. 2.5 mm
• D. 2 mm

Answer: (C)

Thicker filtration removes more low-energy photons, which are the ones that contribute most to the skin dose because they are readily absorbed by superficial tissues. By filtering them out, the beam becomes harder (higher average energy), so fewer photons deposit energy in the skin while still delivering enough higher-energy photons for image formation. Among the options, the 2.5 mm filtration is the thickest, so it removes the most of these low-energy photons and yields the greatest decrease in entrance skin dose. Keep in mind that while this reduces skin dose, it can affect image quality and may require adjustments to technique to maintain receptor exposure.