[Problems of multiple field technique in radiation therapy of cancer of the breast (author's transl)].

A method of adjustment frequently used for postoperative telecobalt irradiation of the mammary carcinoma was verified with the help of film-dosimetric measurements at a phantom. Special interest was taken in the regions with possible overlapping of contiguous fields, where serious complications may occur as a consequence of overlapping. Thus, apposition of several fields requires consideration of the divergence of rays and of the mapping precision of 50%-isodoses in the radiation field, as there lie the principal reasons. For realization of a nearly homogeneous dose distribution, on the one hand, there is necessary parallelism of marginal rays of the neighbouring useful ray beams, the radiation head being tilted laterally by half the angle of aperture; on the other hand, the 50% boundary lines at the light beam localizer have to be shifted parallel by a corresponding distance. In spite of this possibility of optimization, it is distinctly more advantageous, with regard to time and technical aspects, to use a linear accelerator, being additionally applicable for electron pendulum irradiation of the thoracic wall.