The Study Of Setup Errors And Dosimetric Impact For Lung And Esophagus Carcinoma Radiotherapy

Objective:Using KV-cone beam CT(CBCT) on IGRT to study the setup error in patients with lung and esophagus carcinoma radiotherapy and to analyze the effect on target coverage and sparing of organs at risk.Methods:This study includes three stages:(1)25patients with carcinoma of lung and esophagus were enrolled into the study of real-time correction of setup errors using KV-CBCT for a total of239times. XV1were acquired before radiation, witch was the cone beam computed tomography(CBCT), and compared to planned CT images with calculate the setup error of X-axis, Y-axis, Z-axis of the translational errors. Then analyze the changes of setup errors.(2) Use the computer simulation to investigate the effect of translational errors on target coverage and sparing of organs at risk. The setup errors value were3mm、5mm and8mm.Results:(1)25patients received a total of239CBCT scans after initial setup. The systemic±andom errors on translational X, Y, Z directions were (-0.4±2.82) mm,(1.3±5.22) mm,(-0.8±2.18) mm with patients of lung carcinoma and (0.2±2.20) mm,(0.9±4.19) mm,(-0.3±1.92) mm with patients of esophagus carcinoma. The times(%) of the setup errors on translational X, Y, Z directions being within3mm were115(85.18%)、68(50.37%)、118(87.41%) with patients of lung carcinoma and94(90.38%)、60(57.69%)、94(90.38%) with patients of esophagus carcinoma.(2) The result of the computer simulation was as follows:①The influence was remarkable for GTV D95and CTV D95when the center point moved from3mm to8mm in the three dimensional direction.②The dose change of spinal cord Dmax had the statistical significance when the center point moved3mm、5mm and8mm.③Except that it had the statistical significance of the heat MHD when the center point moved8mm in the cranial-caudal direction, all the others hadn’t the statistical significance. The value of heart V30、V40、V50was increased after moving the center point on X-axis, and Z-axis, while it’s opposite on Y-axis. The rang was3.39%～7.51%,4.86%～14.77%,7.17%～19.00%for X-axis、5.02%～12.64%、5.39%～16.58%、27.75%～76.60%for Z-axis and2.13%～6.53%、0.99%～6.33%,0.16%～0.20%for Y-axis. The changes on X-axis and Z-axis was remarkable for V30、V40and V50, having the statistical significance(P<0.05). But the change on Y-axis was unremarkable for V30、V40and V50(P>0.05).④The change range of dose for the double lung MLD is0.02%～1.93%, except that it had the statistical significance for X8、Y5、Y8,the others haven’t the statistical significance (P>0.05). The change range of volume for V5was0～1.59%. The change on Y-axis was remarkable. The change range of volume for V10was0～2.05%. The change on Y-axis was remarkable. The change range of V20and V30is4.61～12.48%,3.34%～21.55%. The change of Y3hadn’t the statistical significance for V2o and the others had the statistical significance. The change of X3、Y3and Z3hadn’t the statistical significance for V30and the others had the statistical significance.Conclusion:(1) Setup errors in the left-right direction(X)、cranial-caudal direction(Y) and anterior-posterior direction(Z) are detected.(2) According to the result of us, the estimated margins required for CTV-PTV are4.9mm for left-right direction、9.5mm for cranial-caudal direc-tion、5.2mm for anterior-posterior direction with patients of lung carci-noma and4.0mm for left-right direction、8.1mm for cranial-caudal direction、3.5mm for anterior-posterior direction with patients of esophagus carcinoma.(3) It has more superiority for CBCT than KV2D. And CBCT can guide radiation treatment accurately.(4) The most influent organs with the dose distribution by the setup errors are spinal cord and heart for patients of esophagus carcinoma, followed by double lung V2o,and the influent is unremarkable for target volume。...