Radiation therapy is a common treatment option for head-and-neck cancer.During the course of external beam radiotherapy of 6-7 weeks, interfraction anatomic changes (tumor regression, weight loss, etc.) and the resulting dosimetric variations were often observed.In this work, we present a real-time GPU-based deformable image registration framework that 1) automatically registers daily volumetric images with the corresponding planning CT image and subsequently generates deformable contours on daily CTs; 2) computes the actual delivered dose to both tumor and normal structures; and 3) documents the actual dose delivered (compared with the plan) for decision making of adaptive therapy.A landmark tool was developed to evaluate the uncertainty in the dose distribution due to registration error.The computation time is ~45 seconds for registering each daily CT to the planning CT and calculating dose accumulation.Clinical implementation of this technology may enable timely plan adaption and potentially lead to improved outcome.