RESUMEN
Objective To compare the clinical target volume (CTV) expanding margins in the mid-and upper-thoracic esophageal carcinoma during radiotherapy measured with and without online image guidance technique by CT on rail.Methods 100 patients with mid-and upper-thoracic esophageal carcinoma undergoing intensity modulated radiotherapy received CT scanning.Image registration was conducted between the scanning results and the planned CT images,thus set-up error data were acquired and got on-line correction.Fifty patients were randomly selected to undergo additional post-treatment CT scanningso as to analyze the revised residuals,displacement during treatment,and infra-fraction GTV shifts.Results Compared to the radiotherapy without CT-based image guidance,the CTV expanding margins obtained with CT-based image guidance was reduced significantly from 9.1,8.8 and 6.1 mm to 4.1,4.5 and 4.3 mm in the left-right,head-feet,and belly-back directions respectively.Conclusions The on-line image-guided technology significantly improves the accuracy of target and reduces the CTV expanding margins.