Abstract
Objective:To analyze positioning errors in patients undergoing radiotherapy at pelvic cavity through compared different fixation methods,so as to select more ideal fixation method that can cooperate with six-degree-of-freedom(6DoF)bed that combined with integrated board,and to provide reference for precisely clinical positioning.Methods:We retrospectively selected clinical data of 59 patients with cancer who received radiotherapy at pelvic cavity at the Department of Radiotherapy,Peking University Third Hospital from June 23,2023 to March 25,2024.Among them,5 cases completed surgery for endometrial cancer,and 5 cases completed surgery for cervical cancer,and 17 cases were primarily cervical cancer,and 27 cases were rectal cancer,and 5 cases were pelvic metastasis.These patients included 16 males and 43 females,whose age ranged from 25 to 79 years(median age was 48 years).Patients were randomly divided into two fixation groups at the time of CT positioning:fixation group that adopted thermoplastic body mesh combined with integrated board(Group A,35 cases)and fixation group that integrated board combined with vacuum bag with negative pressure(Group B,24 cases).Both groups adopted images of cone beam computed tomography(CBCT)to verify positioning errors,and the obtained positioning errors at 6 directions were respectively expressed as x(left-right direction),y(head-foot direction),z(abdomen-back direction),Rx(pitch-rotation direction),Ry(roll-rotation direction)and Rz(left-right rotation direction)to record positioning error before treatment,and error results after calibration.The data of two groups were error within batches,and these data were analyzed and compared.Based on the formula of outward margin,the positioning errors within batches were used to calculate the range of outward margin.Results:The differences of positioning errors before and after calibration in 5 directions except Ry direction for 6DoF bed between two groups were significant(t=6.171,5.200,-16.066,7.259,-3.078,P<0.05).Before 6DoF bed was calibrated,the positioning errors in y(0.13±0.40 cm)and Rx(-0.50±1.80°)directions in group A were less than[((0.20±0.47 cm、0.81±1.54°)in group B,and the differences were significant(t=3.205,-6.822,P<0.05),while there were not significant differences in other two directions(P>0.05).After 6DoF bed was calibrated,the differences of positioning errors in Rr,Ry and Rz directions between two groups were significant(t=-6.297,2.019,-3.711,P<0.05).In addition,the positioning errors in Rx and Ry directions in group A were larger than those in group B,and the positioning error in Rz direction in group A was less than that in group B,and there were not significant differences at the positioning errors in other directions between two groups(P>0.05).Before 6DoF bed was adjusted,the outward margin values of planning target volume(PTV)in x,y and z directions of group A were respectively 0.38,0.61 and 1.01 cm.The PTV outward margin values in x,y and z directions of group B were respectively 0.52,0.83 and 1.02 cm at this time.After 6DoF bed was adjusted,the PTV outward margin values in x,y and z directions in group A were respectively 0.06,0.05 and 0.15 cm,and those in group B were respectively 0.10,0.13 and 0.28 cm.Conclusion:In patients undergoing radiotherapy at pelvic cavity,the application of 6DoF bed that combines with integrated board in fixing patients by using thermoplastic body mesh can improve positioning precision,and significantly narrow PTV outward margin,and reduce the exposure dose to surrounding normal tissues and organs when ensure radiation to tumor.关键词
盆腔放疗/摆位误差/六自由度床/负压真空垫Key words
Radiotherapy at pelvic cavity/Positioning error/6-degree-of-freedom(6DoF)bed/Vacuum cushion with negative-pressure分类
医药卫生
