Objective To analyze the risk factors for positioning errors along different axes in breast cancer radiotherapy and their impact on lung dose.

Methods A total of 103 breast cancer patients undergoing radiotherapy were selected and grouped based on age, surgical approach, tumor location, immobilization method, and body mass index (BMI). The effects of age, surgical approach, tumor location, immobilization method, and BMI on positioning errors in the left-right (X-axis), head-foot (Y-axis), and anterior-posterior (Z-axis) directions were compared. A LASSO regression model was used to analyze the influencing factors of patient positioning errors. A risk scoring model was constructed and validated.

Results Significant differences in positioning errors along the Y and Z axes were observed among different age groups (P ＜ 0.05), while no statistically significant differences were found in other directions (P ＞ 0.05). Among patients of the same age, the positioning error along the Y-axis was greater in the elderly breast-conserving surgery group than in the elderly modified radical mastectomy group (P ＜ 0.05). Among patients of the same age, the positioning error along the Y-axis was greater in the middle-aged left-side group than in the middle-aged right-side group (P = 0.01). Among patients of the same age, the positioning error along the X-axis was greater in the elderly breast support frame combined with thermoplastic mask group than in the vacuum cushion group (P = 0.01). Among patients of the same age, the positioning errors along the Y and Z axes were greater in the elderly obese group than in the normal-weight group (P ＜ 0.05). Age, surgical approach, tumor location, immobilization method, and BMI could explain 10%, 15%, and 15% of the variations in X-axis, Y-axis, and Z-axis errors, respectively (P ＜ 0.05 to P ＜ 0.01). When the setup error in the Y-axis or Z-axis direction exceeded 5 mm, patients were at a higher risk of developing radiation-induced lung injury.

Conclusions Age, surgical approach, tumor location, immobilization method, and BMI are all independent risk factors affecting patient positioning errors in radiotherapy.