Objective To compare the positioning errors and the motion of acromioclavicular joint in breast cancer patients with integrated cervicothoracic thermoplastic membrane and breast bracket fixation,and to provide reference for accurate irradiation of upper and lower clavicular region.Methods Sixty-three pa-tients with breast cancer who were treated in the radiotherapy center of the hospital from November 1,2021 to August 9,2023 were selected as the study objects,and were divided into the integrated cervicothoracic thermo-plastic membrane group(n=32)and breast bracket group(n=31)according to different positioning meth-ods.The translation errors of left and right direction(X),head and foot direction(Y)and ventral and dorsal direction(Z)and the rotation errors of sagittal plane(Rx),cross section(Ry)and coronal plane(Rz)of the two groups were analyzed,and the movement amplitude and three-dimensional displacement of acromioclavic-ular joint were measured respectively.Results Compared with the breast bracket group,X translation errors[(0.18±0.14)cm vs.(0.15±0.12)cm]and Z translation errors[(0.19±0.14)cm vs.(0.16±0.14)cm]of the cervicothoracic thermoplastic memberane group were greater,Z translation error[(0.21±0.17)cm vs.(0.22±0.21)cm]and Rx rotation error of cervical and sternoclavicular joints[(0.93±0.87)° vs.(1.08±0.92)°]were smaller,Rz rotation error[(1.00±0.94)° vs.(0.95±0.86)°]was greater,and the motion ΔX of acromioclavicular joint[(0.18±0.15)cm vs.(0.25±0.21)cm]was smaller,the difference was statistically significant(P＜0.05).Conclusion Integrated cervicothoracic thermoplastic membrane can be used as a solu-tion for prophylactic irradiation of breast cancer in the upper and lower clavicular region and for radiation leak-age in the presence of metastasis.