What describes the influence of electron contamination on PDD in photon therapy?

In photon therapy, the influence of electron contamination on the percentage depth dose (PDD) primarily results in a significant reduction of PDD. When high-energy photons interact with matter, they can generate secondary electrons. These electrons can scatter within the treatment volume, leading to a dose distribution that differs from the intended high-energy photon beam. As these lower-energy electrons are absorbed by the tissue more readily than the deeper-penetrating photons, they lead to a decrease in the effective dose received at greater depths, which ultimately results in a decrease in PDD.

Understanding this concept is crucial in treatment planning and dose calculations, as it emphasizes the importance of accounting for electron contamination to ensure accurate dosing and effective treatment delivery.