Purpose:To quantitatively evaluate the strategic innovation and accuracy variation of deformation registration algorithm for parotid glands using the similarity Dice coefficient during the course of radiation therapy(RT)for nasopharyngeal cancer(NPC).Material and methods:Daily MVCT data for 10 patients with pathologically proven nasopharyngeal cancers were analyzed.The data were acquired using tomotherapy(TomoTherapy,Accuray)at the PLA General Hospital.The prescription dose to the primary target was 70Gy in 33 fractions.Two kinds of contours for parotid glands on daily MVCTs were obtained by populating these contours from planning CTs to the daily CTs via rigid-body registration with or without the rotation shifts using the in-house tools and the Adaptive plan software(Adaptive Plan,TomoTherapy),and were edited manually if necessary.The diffeomorphic Demons algorithm developed in the in-house tool was used to propagate the parotid structures from the daily CTs to planning CTs.The differences of the mapped parotid contours in two methods were evaluated using Dice similarity index(DSI).Two-tailed Pearson correlation analysis was carried out to compare the DSI changes during the course of RT.Results:For 10 patient plans,the accuracy of deformation image registration(DIR)with the rotation shift was obviously better than those without the rotation shift.The Dice scores of the left and right parotids for with and without the rotation shifts were found to be correlated with each other [0.90±0.04 vs 0.91±0.03(r=0.94,p<0.001); 0.91±0.03 vs 0.92±0.03(r=0.94,p<0.001)].The Dice scores for the parotids have shown the reduction with the changes of parotid volumes during RT.The DSI values between the first and last fraction were 0.93±0.02 vs 0.90±0.03 in 10 patient plans.Conclusion:DIR was successfully improved using the strategic innovation for ART.And the decrease of DIR accuracy has also been found during the delivery of fractionated radiotherapy.