The Study Of Spinal Cord Margins In Radiotherapy Of Esophageal Cancer

BackgroundThe spinal cord is an organ at risk in radiotherapy of esophageal cancer.If excessive irradiation occurs,serious consequences will be caused.Therefore,the correct evaluation and control of its exposure dose is the key concern of radiotherapy.Based on the characteristics of fractional radiotherapy,clinical target volumes and organs at risk need to be drawn margins to ensure sufficient dose coverage of the tumor and effective protection of organs at risk.For spinal cord margins,the current majority of radiotherapy centers adopt a unified recommended margin for spinal cord,which may not consider the subsegment of the spinal cord and what radiotherapy techniques are used,We try to conduct segmental analysis and calculation according to the latest image-guided technology and the designation of vertebral body.ObjectiveAccording to the diagnostic CT image,the setup error and residual of spinal cordwere segmented analysis to determinewhether the spinal cord needed to be segmental margins.MethodsAccording to the treatment site,a total of 60 patients with esophageal cancer in the cervical group,thoracic group and abdominal group were selected,and all of them underwent image-guided radiotherapy.The neck group were fixed with a thermoplastic mask,and both the chest groupand the abdomen group were fixed vacuum bags.Intensity modulated radiotherapy(IMRT)technology was adopted,and pre-treatment verification images obtained by CTVision accelerator diagnostic spiral CT were used.Images of eachcase were collected for 20 consecutive times,all in the online image guidance mode.Import CT image on MIM software,process and extract positioning parameters;The Dice coefficients,Hausdorff distance maxima and centroid coordinates of the delineated spinal cord were processed and extracted.The compatibility variance test and Friedman M test were used to analyze the data.The formula for calculating marginsof organs at risk was MPRV=1.3 ? total +0.5? total.ResultsThe setup errors ofcervical,thoracic,and abdominal spinal cords were increased in turn before usingimageguidance.The dice coefficient of cervical,thoracic and abdominal spinal cord were increased in turn after using image guidance,the hausdorff distance were decreased in turn,the mass center deviation was the largest in the neck,the smallestin the chest.The setuperror of the spinal cord before image guidance was different in general,and the differences between the neck,chest and abdomen were obvious,but the difference between the chest and abdomen were not statistically significant.After image guidance,the deviations of the centroid of each segment of spinal cord were generally different,and the differences between cervicothorax and thorax were obvious,but the differences among cervicothorax and thorax and abdomen were not statistically significant.After image guidance,the hosidorff distance of each segment of spinal cord was generally different,and the differences between cervicothorax and cervicoabdomen were obvious,but the differences between chest and abdomen were not statistically significant.Multiple comparisons of parameters of any spinal segment before and after image guidance were statistically significant.The positionsof centroid method for using image-guided correction of anterior cervical,thoracic and abdominal spinal cord were X,Y and Z were 3.44,5.09,6.12;3.45,3.42,4.16;3.66,4.51 and 6.84 mm,respectively;By image-guided registration of posterior cervical,thoracic,and abdominal spinal cord centroid methods,X,Y,and Z were reduced to 1.87,1.33,2.24;1.71,1.37,2.24;1.89,1.35,1.29 mm,respectively.The X,Y and Z positions of hausdorff distance method for image-guided correction of anterior cervical,thoracic and abdominal spinal cord were 2.57,5.04,5.90;2.81,3.35,4.27;2.87,4.44,6.65 mm,respectively;The X,Y and Z residual exodulation of the image-guided registration of thecervical,thoracic and abdominal spinal cords were reduced to 1.23,0.93,1.55;1.23,0.93,1.55;1.23,0.93,1.55 mm,respectively.ConclusionAll segments of spinal cord image-guided correction have different anterior setup error and postregistrationresidual,so different values of margins should be given.