In the field of radiotherapy, methods for dose or treatment planning for a radiation therapy system having a collimator, includes determining shots to be delivered during said treatment, each shot being associated with an isocenter and being modelled by a spatial dose volume distribution of radiation, the shape of said spatial distribution depending on the specific collimator setting and said selected dose level, including selecting isocenter positions within a target in a predetermined angle range； evaluating each isocenter based on predetermined conditions； selecting at least a specific collimator and sector setting for each isocenter based on the evaluation； calculating a dose for the selected isocenters； repeating the steps until at least one stopping criteria has been reached, wherein a final set of isocenters are provided； and using the final set of isocenters in treatment planning.
