Total body irradiation (TBI) combined with intensive chemotherapy and bone marrow transplantation is used with increasing success for the treatment of hematologic malignancies with severe prognosis. An expert system, developed on the basis of the experience acquired during the last years in our department, has been designed to optimize the different treatment steps. The choice of an expert system is based on its capabilities in reconstructing a rule-based reasoning through the combination of theoretical and empirical knowledge. Particularly, a subsystem dealing with the steps to be taken to optimize treatment in TBI has been designed using medical and physical data. Our system can determine radiation treatment variables together with a sequence of quality control procedures. Moreover, indications are given about short, medium and long term damage probabilities and toxicity estimates, both derived from literature data and our personal series of cases. Treatment quality can be assessed and the different techniques compared using these data. This project is aimed at providing physicians and physicists with useful clinical suggestions for TBI setting for bone marrow transplantation.