Analytic fits to Monte Carlo calculated depth-dose curves of 1- to 50-MeV electrons in water

An analytic expression is given for depth-dose curves of plane-parallel electron beams normally incident on semi-infinite water absorbers with initial energies from 1 to 50 MeV. The expression consists of two terms representing the main component due to collision energy-loss of primary electrons and the component via radiative process. To study the profile of the bremsstrahlung component, Monte Carlo calculations have been made with the MCEF code. The results show that this component has a maximum around 0.9r0, where r0 is the csda (continuous slowing-down approximation) range of electrons in water. Values of the constants in the main term have been determined so as to minimize the deviations of the expression from the depth-dose data calculated with three Monte Carlo codes (MCEF, EGS4 and ITS). The maximum value of the deviations is from 0.7 to 3.5% of the maximum dose at each energy, and is less than or comparable to the maximum deviations among the different Monte Carlo results. (orig.)