What is the approximate therapeutic depth for a clinical electron beam of most probable energy E (MeV)?

The therapeutic depth for a clinical electron beam is generally approximated as a function of its energy. Specifically, the depth at which the dose maximizes is typically around one-fourth of the beam's energy in MeV. This relationship stems from the properties of electron beams, which lose energy as they penetrate tissue and have a specific range that is influenced by their initial energy.

When electrons are used in radiation therapy, their therapeutic depth is crucial for determining how effectively they can treat tumors while minimizing damage to surrounding healthy tissue. The depth at which the dose is delivered is significant for clinical applications, and using one-fourth of the energy provides a practical rule of thumb for estimating this therapeutic depth.

Higher energy beams penetrate deeper, while lower energy beams have a more shallow range. The approximation of one-fourth efficiently balances the characteristic behaviors of electrons, making it a commonly accepted guideline in medical dosimetry for estimating the depth of maximum dose deposition.