Application of optical surface-guided positioning in breast-conserving radiotherapy

LIU Jin-di; ZHU Qiu-fang; WANG Ya-juan; HE Zhen-yu; CHEN Xue-mei

doi:10.13820/j.cnki.gdyx.20232705

Abstract：Objective To evaluate the accuracy of surface guided radiation therapy(SGRT)in daily positioning of breast-conserving radiotherapy.Methods Retrospective analysis was performed on 40 breast cancer patients who un-derwent ELEKTA infinity accelerator radiotherapy.Patients were positioned by the optical surface monitoring system(OSMS).The first three fractions and once weekly cone-beam computed tomography(CBCT)images were retrieved for data analysis.The couch parameters of the OSMS positioning,CBCT registration and the skin markers were recorded in lateral(ML),longitudinal(SI)and vertical(AP)directions,respectively.The difference between the surface guidance(SG)of OSMS and CBCT and the skin marker(SM)of CBCT was calculated and compared.The results were compared using nonparametric tests,and the rotation of SG positioning and the proportion of SG and SM were statistically analyzed.The Bland-Altman plot was used to analyze the consistency between SG and CBCT.Planning target volume(PTV)mar-gins(M)were calculated using the formula MPTV=2.5Σ+0.7σ.Results The median errors in the ML,SI,and AP translation directions for SG(0-0.1 cm)were smaller than those for SM(0-0.3 cm),with statistically significant differences(P＜0.05).The proportion of absolute values of errors ≤0.3 cm in the ML,SI,and AP directions for SG was 14.8％,16.3％,and 35.1％higher,respectively,than for SM.The median range of Pitch,Roll,and Yaw rotation errors for SG positioning was(-0.10-0.10)°.In the Bland-Altman scatter plot,the mean differences between SG and CBCT in the ML,SI,and AP directions were 0.03 cm,0.01 cm,and 0.13 cm,respectively.The M values for SG and SM in the ML,SI,and AP directions were(0.36 cm,0.38 cm,0.30 cm)and(0.66 cm,0.82 cm,0.93 cm),respec-tively.Conclusion In breast-conserving radiotherapy for breast cancer,SGRT-guided positioning can effectively re-duce positioning errors,decrease the external expansion boundary of the PTV,and demonstrate good consistency with CBCT.