Why are therapy x-ray beams used in kV considered to need medium filtration?

The use of medium filtration in kV therapy x-ray beams is primarily motivated by the need to reduce the skin dose by removing low-energy photons. Low-energy photons do not contribute significantly to the therapeutic effects of radiation therapy; rather, they increase the amount of radiation that is absorbed in the skin, leading to unnecessary skin dose and potential toxicities. By incorporating medium filtration, the beam's energy can be optimized to diminish these low-energy photons while preserving the effectiveness of higher energy photons that are more beneficial for treatment. This approach not only enhances patient safety by minimizing skin exposure but also focuses the therapeutic effects deeper in the tissue where it is most needed.

The other options do not directly relate to the primary purpose of medium filtration in therapeutic x-ray applications.