How does the skin dose change with increasing electron energy in a clinical electron beam?

With increasing electron energy in a clinical electron beam, the skin dose tends to increase. This phenomenon is primarily due to the physics of electron interactions with matter. Higher energy electrons are able to penetrate deeper into biological tissues, which leads to a greater energetic transfer in the initial layers of skin.

As the energy rises, the maximum range of the electrons increases, allowing for a larger volume of tissue to be more effectively irradiated. This increase in energy results in a higher dose delivered to the skin because the electron beam can produce a denser distribution of ionization events along the path, especially during the initial interaction.

Additionally, clinically, higher energy electron beams are used for tumor treatments that are situated close to the surface, allowing for therapeutic doses to be administered to the tumor while managing the dose delivered to surrounding healthy tissue. The increase in skin dose with higher energy therefore reflects a strategic choice in treatment planning, designed to optimize the balance between tumor control and sparing nearby healthy tissues.