Application of scattering foil systems for forming large-sized uniform electron therapy fields

The methods of forming extended fields in electron therapy using foil systems for scattering electron beams from the LUE-25 medical linear accelerator are discussed. Procedures for calculating shadow compensator parameters are presented. The role of the initial electron beam size in the choice of the parameters of scattering and compensating filters is evaluated. Advantages offered by this beam shaping technique for reducing the bremsstrahlung background level are considered. The experimental results show that highly uniform dose fields can be formed, if shadow compensating systems are used. The depth dose distributions of 27-MeV electrons obtained with a defocusing magnet system and with a system of scattering foils and compensators are compared.