[Calculation of rotating field isodose lines without spike artefacts (author's transl)]

When rotating fields are calculated by addition of a series of fixed fields, the resulting isodose lines often show spike artefacts. To avoid these, the fixed fields can be substituted by real rotating field increments. Significant differences between fixed fields and rotating field increments are found only in the penumbral region, where the smearing effect of the rotation makes the slope less steep. A method is introduced for the calculation of dose distributions in rotating field increments using a "smeared penumbral function".