1. A method for tracking a target, the method comprising: receiving a planning image of a patient including the target, wherein the planning image has a first coordinate system; acquiring a diagnostic image of the patient in a second coordinate system, wherein said diagnostic image includes at least a portion of the target; acquiring a first tomosynthesis image of the patient in the second coordinate system, wherein the first tomosynthesis image is inherently registered with the diagnostic image, and wherein the first tomosynthesis image includes at least a portion of the target; registering the diagnostic image with the planning image to obtain an alignment transformation between the first coordinate system and the second coordinate system; acquiring a second tomosynthesis image of said patient, wherein said second tomosynthesis image includes at least a portion of the target; registering said second tomosynthesis image with said first tomosynthesis image to compute an intrafraction transformation between the first coordinate system and the second coordinate system, wherein said intrafraction transformation determines an approximate intrafraction location of the target in the second coordinate system relative to the first coordinate system; and delivering treatment radiation to the target based at least in part on said intrafraction transformation and said alignment transformation.