[en] The area of the bladder base where late radiation reactions following intracavitary irradiation of a cervix carcinoma most frequently occur is not well indicated by means of the balloon of a Foley catheter which is commonly used as a marker for dosimetry. Therefore, a thin metal chain is inserted and positioned at this part of the bladder base. Dosimetry is performed with the aid of sets of precalculated isodoses on transparencies placed upon the laterally taken radiograph. On the average, the dose predicted with aid of the chain is found at an 11% higher level compared to the dose determined with the balloon. In order to avoid the insertion of a chain, which is less easy than that of a balloon, it has been proposed to replace the marker point of the balloon by another point obtained by shifting over 10 or 15 mm into cranial direction. However, measurements from 50 applications showed that this replacement does not provide reliable results. (Auth.)