Determining a treatment plan with the shortest possible period of irradiation of a particle irradiation facility

The invention relates to a method and a device (10) for determining a radiation treatment plan for a particle irradiation unit (20). In this case, depending on a target volume of the treatment plan (6) within an examination object (14; 18) with the particle irradiation unit (20) irradiated with a particle beam (16). The radiation schedule is determined to apply the energy of the particle beam (16) in accordance with a predetermined dose distribution in the target volume (6), wherein the target volume (6) and the predetermined dose distribution are given. A determination of the radiation treatment plan is additionally taken into consideration, an irradiation period, the radiation treatment plan is determined such that the irradiation time is as short as possible.