1. An imaging method, implemented by a computing system programmed to perform the following, comprising: acquiring measurement data indicative of a target motion, wherein the measurement data includes a prior x-ray image; determining, using the computing system, a timing of one or more x-ray images based on the target motion; computing a time to completion of a radiation treatment beam; comparing an age of the prior x-ray image to the time to completion; and when the age of the prior x-ray image will exceed an image age threshold before the time to completion, acquiring a new x-ray image before delivering the radiation treatment beam.