Systems and methods are provided for registering images. The systems and methods perform operations comprising: receiving, at a first time point during a given radiation session, a first imaging slice comprising an object, the first imaging slice corresponding to a first plane; accessing, at the first time point during the given radiation session, a composite imaging slice corresponding to the first plane, the composite imaging slice being generated using a plurality of imaging slices obtained prior to the first time point; spatially registering the first imaging slice and the composite imaging slice; determining movement of the object using the spatially registered first imaging slice and the composite imaging slice; and generating an updated therapy protocol to control delivery of a therapy beam based on the determined movement.