A method of providing intensity modulated radiation therapy to a moving target is disclosed. The target moves periodically along a trajectory that is projected onto a multi-leaf collimator (MLC) plane. The MLC plane is divided into thin slices parallel to the movement of the target. The present invention optimizes the leaf sequence such that, within each slice, if a point receives radiation, all other points in that slice that receive the same amount or more fluence are also receiving radiation at the same time.