[Optimization of dose distribution in whole body irradiation by means of compensators]

In case of whole-body irradiation prior to bone marrow graft, an undesired irregular dose deposition in the median body plane is caused by the irregular body shape and the tissue inhomogeneities of the patient, which can amount up to 50% of the planned focal dose in case of laterally opposing irradiation. A procedure is proposed allowing to modify the dose distribution in the irradiated body systematically by means of compensators. Such compensators are produced with the aid of an adequate number of serial CT scans, a programme system considering these data and the individual irradiation geometry, and a computer-controlled cutter working in three dimensions. First a casting mould is manufactured which is then filled up with an adequate compensation material. The actual compensation data and the planned irradiation geometry are controlled before and during the treatment. Taking into consideration the individual shapes and the different tissue densities, it is not only possible to prevent the dose inhomogeneities mentioned above but also to introduce by means of a special programme part regions with a higher or lower dose deposition at any point of the irradiation field, at the therapeutist 's discretion.