Study of the backscattering of electron beams with energies typical of radiotherapy

Abstract

During radiotherapy, the dose of electrons backscattered into the tissue should be taken into account. According to the available data on the electron backscattering phenomenon, the backscatter rate varies depending on the specific radiotherapy delivery configuration. Using the Monte Carlo code MCNPX, the backscattering distribution and their saturation values for electron beams with energies between 4 MeV and 25 MeV (the energies used in electron therapy) of various materials such as polystyrene, aluminum, copper and lead were obtained. Data obtained with MCNPX show that the probability of electron backscattering is strongly dependent on the effective atomic number and the energy of the electron. For low energy electrons, the backscattering probability depends less on the energy and is mainly a function of the effective atomic number of the backscatter material. The saturation values of the backscattering are distributed as a linear function of the effective atomic number of the scattering material for all investigated energies. Therefore, it is recommended that equipment and accessories used with patients in electron radiotherapy LINAC be materials with low atomic numbers (Z), and that a layer of low Z material be used over a higher Z material for protection.