Identification Of Two Methods Of Fixation In Radiotherapy Of Upper Cervical Thoracic Esophageal Cancer Analysis Of Setup Error

Objective Through CBCT image guided on-line verification and comparison of the two fixed methods,the positioning error between the head and neck thermal plastic mask and the negative pressure vacuum pad in the upper cervical thoracic esophageal cancer radiotherapy process,through the analysis of pendulum error regularity to explore the feasibility of the design of individualized radiotherapy.Methods From January 2016 to February 2018,40 patients with cervical and upper thoracic esophageal carcinoma were randomly fixed with head and neck mask and 20with vacuum pad.In both groups,the same 16-row helical CT analog locator was used in their respective positions.The CT TLC scan of the neck and chest was carried to the Ivview GT workstation.The target area was mapped by the clinician and then confirmed by the lead physician.The three dimensional coordinates of the patient's treatment pendulum can be expressed by X,Y and Z respectively.After the treatment plan is completed,the patient is transferred to the computer room Warlian linear accelerator and treatment begins.Each patient was verified by CBCT during treatment,5 times before treatment,3 times after radiotherapy,and 13 times per patient.The real-time pendulum image obtained by scanning is matched with the planned image,and the pendulum error of X,Y and Z is obtained.If the error is found,it can be corrected automatically by computer,and the pendulum error in X-axis,Y-axis and Z-axis of the two groups can be analyzed.And compare and analyze the pendulum error of 5 times before treatment and 8 times after treatment.Results The position of the two groups in the direction of the X axis was statistically significant,while the position errors in the direction of Y and Z axis were not statistically significant(P_X=0.033,P_Y=0.518,P_Z=0.284).There was no significant difference between the first 5 times and the last 8 times(head and neck mask group:P_X=0.445,P_Y=0.959,P_Z=0.676).Vacuum cushion group:P_X=0.967,P_Y=0.404,P_Z=0.738).Conclusion For patients with cervical and thoracic esophageal carcinoma,radiotherapy,head,neck and shoulder thermoplastic membrane and negative pressure vacuum pad are two representative fixed devices.This study shows that there is no significant difference between the two sets of fixed devices in the Y-axis and z-axis,while the position error on the X-axis is better than that of the vacuum pad.There was no difference between the two fixations with the time of treatment.Therefore,according to the patient's setup error data of the first 5 times,we can calculate the scope of PTV,redesign the individualized radiotherapy,reduce the scope of PTV,effectively avoid the blind external radiation,and improve the accuracy of radiotherapy.