[en] With HDR (high dose rate) afterloading treatment, a very critical dependence of normal tissue reaction (rate of side effects of organs at risk) on dosage was demonstrated compared with the effect of low dose rate application. Furthermore, a stronger dependence of normal tissue reaction (steeper curves) on application of a single HDR afterloading fraction compared with that on total dose application over several weeks was observed. All these observations require exact dosage of HDR afterloading application to all points of organs at risk concerned in order to compensate the radiobiologically critical dosage of HDR. On the other hand, a threshold of 7 to 7.5 Gy per single fraction at organs at risk should not be exceeded. Therefore, HDR afterloading treatment requires optimization of source arrangement or source movement in order to receive good results. Since 1976, computer optimization of the movement of a highly active Ir-192 source is used, since 1987, an IBM PC AT is used for this calculation. The computer optimization programme, its data output and isodose calculation parts, is briefly discussed. 3 refs.; 5 figs