The influence of pulmonary tissue on dose distribution in fast electron radiotherapy

The influence of pulmonary tissue on dose distribution in the radiotherapy with fast electrons in a water phantom as well as in a heterogeneous phantom was determined. Empirical relations were derived from the measuring results. They allow the consideration of the dependence of the correction factor on the main parameters of irradiation such as radiation energy, field size, depth of the pulmonary tissue, depth of the point to be calculated and source-surface distance. It follows that without consideration of this dependence for a dose calculation in the lung an error of 30% related to the maximum dose may arise. The given method made it possible to decrease this error to 5%. Furthermore, the effect of a changed position of the radiation source is considered in dependence on radiation energy and on the field size which is caused by electron scattering on the forming equipment. (author)