A method for stereotactic radiosurgery planning by information extraction from CT-images is presented. Information extracted from the CT-images is used to calculate the stereotactic approach and the three dimensional dose. distribution for a brain tumour, which is to be treated. by interstitial radiosurgery. Computer programs have been developed which allow a fast interactive treatment planning and the visualisation of the information which is necessary for surgery and radiation dosimetry. The described procedure is a combination of different image processing, reconstructing and display techniques with the aim of precise, stereometrical information extraction.