Setup accuracy and dosimetric analysis of surface-guided radiotherapy in hypofractionated radiotherapy for breast cancer

ZHANG Weiheng; ZHAO Xuehui; ZOU Bing; LI Qing; ZHOU Zhenyu; LAN Qiongyu

doi:10.19300/j.2026.L22196

Abstract：Objective To evaluate the setup accuracy of surface-guided radiotherapy(SGRT)in hypofractionated radiotherapy for breast cancer,to quantify the relationship between setup errors and target dose distribution,and to determine setup error control thresholds according to different planning target volume(PTV)sizes.Methods Sixty female patients with breast cancer who underwent breast-conserving surgery and completed hypofractionated radiotherapy were retrospectively enrolled.According to the treatment guidance method,patients were divided into a conventional setup group(n=30)and an SGRT group(n=30).Setup errors between the two groups were compared using the Mann-Whitney U test.Spearman correlation analysis was performed to assess the association between SGRT-derived setup errors and cone-beam computed tomography(CBCT)registration errors,followed by linear fitting using ordinary least squares regression.Dose variations caused by simulated setup errors were evaluated using the Eclipse treatment planning system.Pearson correlation analysis was applied to investigate the linear relationship between PTV volume and actual delivered dose under different setup error conditions.Results Setup errors along the X,Y,and Z axes in the SGRT group were significantly smaller than those in the conventional group(all P<0.05),and the three-dimensional setup errors of all SGRT cases were<0.4 cm.SGRT-derived setup errors showed a strong positive correlation with CBCT-based registration results(r=0.81-0.91,all P<0.001),demonstrating high consistency between the two methods.Dosimetric simulation revealed that when the overall setup error exceeded 0.4 cm,target dose deviations increased markedly,with the Z-axis showing the highest sensitivity.Significant axial differences were observed in the linear correlation between PTV volume and delivered dose.For the Z-axis,a moderate correlation was identified at setup errors of 0.4 cm and±0.5 cm,and a weak correlation at-0.4 cm.For the X-axis,a weak correlation was observed at-0.4 cm and-0.5 cm,whereas no significant linear correlation was found for the Y-axis at any setup error level.Notably,in patients with PTV<400 cm³,the Z-axis setup error should be controlled within 0.2 cm.Conclusion SGRT provides accurate,safe,and non-invasive guidance for hypofractionated radiotherapy in breast cancer,reducing radiation exposure and patient psychological burden while improving workflow efficiency.Setup error thresholds along the Z-axis should be individualized based on PTV volume to ensure optimal dose delivery.