The authors have examined in an experimental study what influence is exerted by the width of the boundary line between two adjacent fields and by the dose inhomogeneity on the suture points lying in the region of the target volume. The results of this study are presented and the influence exerted on the dose distribution by different diaphragm sizes is shown by means of longitudinal and cross sections. The conclusion for the practical application of radiotherapy is that there exists a possibility to obtain homogenous dose distributions also beyond the borders of the field.