A study on factors influencing setup errors in breast cancer radiotherapy based on age groups and surgical types

Purpose To investigate the impact of age, breast laterality, and surgical type on setup errors in breast cancer radiotherapy. Methods A total of 490 patients with breast cancer who underwent breast-conserving surgery or modified radical mastectomy followed by radiotherapy at our hospital between November 1, 2019, and April 2, 2025, were retrospectively enrolled. Patients were divided into three age groups: younger, middle-aged, and elderly. Setup errors were compared among the groups. A linear mixed model (LMM) was constructed incorporating baseline patient characteristics to identify potential factors influencing setup errors. Results For all age groups, the CDF curves of setup errors in three dimensions were consistent, symmetric about zero, and steep, indicating concentrated errors. In subgroup analysis, the X-direction CDF curve for younger patients in the MRM group and the Y- and Z-direction CDF curves for younger patients in the BCS group showed negative shifts. Linear mixed model analysis showed that BMI (p = 0.019), age (p = 0.017), and clinical stage (p = 0.007) were all significantly associated with setup errors in the Y direction. Conclusion The factors influencing Y-direction setup errors in breast cancer radiotherapy vary by surgical procedure: in the modified radical mastectomy (MRM) group, BMI was the independent factor; in the breast-conserving surgery (BCS) group, age and clinical stage were the independent factors. Advances in knowledge This study employed a linear mixed model, providing clinical insights into setup errors in breast cancer image-guided radiotherapy, and identified the factors influencing Y-direction positioning accuracy.