[Dose distribution and irradiation technique in the radiotherapy of breast cancer stage I].

A method for homogenous irradiation of the breast by means of opposite standing fields, with the use of wedge filters, is described here. The field is focussed so that the interior thoracic wall under symmetric position of the mamma is still completely situated in the irradiation field, and the lateral area of the ray beam passes 1-2 cm into the pulmonary tissue. On a series of typical breast models, made under consideration of the irradiation position, the isodose distributions were determined by film-dosimetry. The therapeutically most important 80%-isodose corresponds in practically every case with the mamma contour. Peak doses or areas of underdosage were not observed. The thoracic wall is still exposed to about 75% of the maximum dose. In order to reach a more accurate irradiation by the desired maximum dose of, for example, 250 r, the deviation of which does not exceed plus or minus 7%, it is necessary, at the beginning of an irradiation series, to use ionisation chamber measurements with an intensifying hood on the surface of the mamma, 1.5 cm above the border of the field. In the case of lateral irradiation, the measurement need only be made laterally, in medial irradiation it is only necessary on the medial side. The portion of the dose affecting the opposite field on the measuring place can be calculated by the use of depth dose tables. From the values so gained the desired maximum dose within the mamma may be ascertained by multiplication by the factor 1.03.