An analytical expression for electron beam central axis depth doses.

An analytical expression based on four fitting parameters is proposed for a mathematical description of electron beam central axis depth dose distributions. The expression approximates well the measured electron beam data in the field size range from 4 x 4 cm2 to 25 x 25 cm2 and in the energy range from 6 to 20 MeV in all four regions of the electron depth dose curve: build-up, dose maximum, dose fall-off, and bremsstrahlung contamination.