The aim of the invention is to provide a planner with the opportunity to effect local improvement of an IMRT treatment plan which is available to him. To this end, a method for customizing a dose distribution setting for a technical appliance in tumor therapy is proposed. A first plan (10) is read from a data memory (100). The first plan (10) for dose distribution in a plan volume (Z) is presented on a presentation device (110), the reason for this being the possibility of setting the technical appliance for tumor therapy to dispense the set dose distribution to a patient. The presentation is made for the purpose of changing the first plan (10) in at least one degree of fineness (10a) specific in terms of volume and for producing or ascertaining a causal follow-up plan for the setting on the technical appliance for tumor therapy. It is possible to prescribe a new dose value for a local/small group of voxels (z) in the or as the degree of fineness (10a) specified in terms of volume at a particular point in the plan view (Z) which does not have this new dose value. The particular point is stipulated by selecting an initial voxel (z1) which is situated in a layer (yi) of the plan volume. The first plan (10) is converted into a first navigation plan (11). This conversion takes account of the first plan (10) and the change of dose in the small/local voxel group. The first plan (10) or the first navigation plan (11) is presented on the same presentation device (110), depending on a setting on a first operating aid (40) with two end positions (41, 42), wherein the first end position corresponds to the first plan and the second end position (42) corresponds to the first navigation plan.