Adaptive radiation therapy (ART) is a close-cycle radiation therapy using various measurements' feedback to modify the initial plan. It intends to improve radiation therapy by systematically control the variations during the course of treatment and use them to reoptimize the initial plan. In this process, beam field and delivery dose should be routinely customized to each individual patient so that they can achieve a much safer dose escalation. This paper introduces the background and basic concept of ART, and discusses the basic ART method,...