[Dose distribution in a linear moving-field irradiation]

The authors discuss the effects of a linear moving field irradiation. It is demonstrated that the depth dose curves and the longitudinal field profiles of this irradiation method are considerably modified with respect to a stationary field of the same superficial field size. Especially the depth dose attenuation becomes less abrupt. The reason therefore is of merely geometrical nature and does not depend on the type of radiation. For example, a cobalt field with a focus-skin distance of 60 cm and a superficial field size of 10 x 10 cm2 has a half-value depth of 10.3 cm in case of a stationary field and of 12.0 cm in case of a linear moving field.