Which primary patient dose measurement is influenced by filtration?

• A. Effective dose
• B. Gonadal dose
• C. Mean organ dose
• D. Entrance skin dose

Answer: (D)

Filtration works by removing the lowest-energy photons from the X-ray beam, hardening the spectrum. Those soft photons deposit most of their energy in superficial tissues, so reducing them lowers the energy delivered to the skin. Entrance skin dose is the dose measured at the surface where the beam enters, and it is the metric most directly affected by the beam’s spectral quality. While filtration also influences doses to deeper organs, the change is less pronounced for them, and effective dose is a broader, population-based measure that depends on multiple organs. So filtration mainly reduces the dose right at the skin entrance, making entrance skin dose the best answer.