In the field of radiotherapy, methods for dose or treatment planning for a radiotherapy system including a radiotherapy unit are described. A spatial dose delivered can be changed by adjusting beam shape settings, wherein delivered radiation is determined using an optimization problem that steers the delivered radiation according to objectives reflecting criteria for regions of interest including at least one of: targets to be treated during treatment of the patient, organs at risk and/or healthy tissue. The method includes determining an inner set of voxels and providing a first frame description for the inner set of voxels, where the first frame description reflects criteria for the inner set of voxels. Determining an outer set of voxels encompassing the target volume and the inner set of voxels and a frame description for the outer set of voxels is provided where each reflecting criteria for the outer set of voxels. The frame descriptions are then used in the optimization problem that steers the delivered radiation.
