Clinical Analysis Of Set-up Errors Between Two Fixation Devices For Intensity Modulated Radiation Therapy (IMRT) After Breast Conserving Surgery Of Breast Cancer Based On Cone-beam CT

Objective: The set-up errors is an important factor which effects intensity modulated radiation therapy(IMRT)after breast conserving surgery of breast cancer.Significant Set-up errors reduction can be achieved with the use of Suitable fixation devices.This study investigates the set-up errors between the body film combined with the breast bracket and the body holder before intensity modulated radiation therapy after Breast Conserving Surgery of Breast Cancer based on Cone-beam CT to get a better position immobilization.Methods: The clinical data of 34 patients from November 1st,2017 to February 25 th,2018 received IMRT after breast conserving surgery in the Affiliated Tumor Hospital of XinJiang Medical University were enrolled in the study.Then they were randomly divided into two groups.Group A were applied with breast bracket for positioning and group B with body holder.Based on the onboard CBCT,set-up verification was performed per week for each patient before IMRT treatment.The CBCT image was automatically matched with the CT simulation image.And the set-up variations in three dimension,X(left and right),Y(upper and lower),Z(front and rear)axes,were measured.Results: All 34 cases were given 196 times of CBCT scanning before treatment,the set-up error of X(left and right)axes of group A was(1.64±1.30)mm,Y(upper and lower)axes was(1.29±0.94)mm,Z(front and rear)axes was(2.41±1.53)mm.By the same token,set-up error of X(left and right)axes of group B was(2.10±1.73)mm,Y(upper and lower)axes was(1.76±1.47)mm,Z(front and rear)axes was(3.12±1.74)mm.The t-values in X,Y and Z directions were 2.093,2.659 and3.048,respectively(P=0.038,0.009,0.003),compared the two groups had a significant difference.The set-up errors of group A on X axes were 91.8% in<3mm,7.1% in 3~5mm,1.0% in>5mm,on Y axes were 99.0% in<3mm,1.0% in 3~5mm,0%in>5mm,on Z axes were 81.6% in<3mm,15.3% in 3~5mm,3.1% in>5mm.Similarly,the set-up errors of group B on X axes were 82.7% in<3mm,9.2% in 3~5mm,8.2% in>5mm,on Y axes were 88.8% in<3mm,7.1% in 3~5mm,4.1%in>5mm,on Z axes were 55.1% in<3mm,34.7% in 3~5mm,10.2% in>5mm.Conclusions: Breast bracket is superior to the body holder for IMRT after breast conserving surgery of breast cancer and that is recommended for position immobilization in whole breast radiation.