The rapid progress of computer technology, especially the increasing power of image processing systems, has opened up new possibilities for future development of computer systems in the medical field. Some research centers like DKFZ in Heidelberg, the Joint Center for Radiation Therapy at Harvard Medical School and the Massachusetts General Hospital in Boston, have for many years been working with software development using the most modern techniques for planning of radiotherapy. A Nordic development program, CART (Computer Aided Radio Therapy), started this year as a joint project between Nordic industry, research centers and radiotherapy/radiation physics departments. The scope is to define general concepts for information transfer in a radiotherapy clinic. The different disciplines (applications) will also be investigated at 4 development centers and after a 2 years study functional prototypes will be presented. This paper will focuse the problem of computers in radiotherapy, keeping in mind the Nordic CART project and especially image handling problems.