[Inhomogeneity of electron beam dose distribution]

The radiation therapy employing high energy electron beams took place in superficial or near-superficial target volume treatments. The author describes the dose distribution in the patient whose body is not homogeneous for the presence of bone structures or air cavities that may involve localised perturbations of the dose distributions. Several methods have been developed to obtain the correct dose distribution including the influence of depth, field size and energy. The author describes how the dose distribution changes when the body contour at the beam entrance is bent and oblique. Artificial inhomogeneity like compensators, bolus and adjacent electron beam field may give unexpected small overdose areas.