The method involves pre-determining a target volume to be irradiated and a condition (55) to be fulfilled and carrying out an optimization process (61) by preparing data set (62) and determining parameter set (65,66,67,68). An irradiation planning data set (83) is produced by additional parameter set (75,76,77,78). Independent claims are also included for the following: (1) an irradiation planning device with a computer unit and (2) an irradiation system, particularly particle therapy system with a controlling device.