A medical data processing method for determining a target set comprising at least one irradiation target in a patient's body for radiation therapy treatment by means of a treatment device constituted to treat the at least one target by means of one or more sub-beams during a treatment time, the one or more sub-beams constituting at least one treatment beam which is to pass through the at least one target in accordance with a treatment plan during the treatment time, the method comprising the following steps and being constituted to be executed by a computer: a) acquiring (S 1.1) critical area; b) acquiring (S 1.2) target data; c) acquiring (S 1.3) treatment beam constraint data; d) acquiring treatment beam criteria data (S 1.4); and e) determining (S4), based on the critical area data, the target data, the treatment beam constraint data and the treatment beam criteria data, target set data describing spatial information on at least one irradiation region.