Abstract
In stereotactic irradiation using linear accelerator, lateral electron equilibrium must be considered for smallest field. The dosimetry has some problems, for example, the accuracy of measurement depend on detector volume. Therefore comparison between theoretical and experimental techniques is important. It has previously been shown that broad beam dose calculation models for high energy x-rays can be described by transport of secondary electrons introducing the electron disequilibrium factor. In this study, theoretical calculation of the electron disequilibrium factor was performed at four different beam qualities. Experimental measurements of electron disequilibrium factors of longitudinal and lateral components showed that they depend on depth Z and field radius R, respectively, such as E(Z, R)=E_z(Z)・E_R(R). As a result, a model for the E(Z, R)-factor explains well measurements for different beam energies. It suggests that the parameters of the theoretical model depends on the dose averaged linear attenuation coefficient.
