Influence of Site, Surgery, and BMI Binary Classification on Positioning Errors in Radiotherapy for Breast Cancer Patients: A Retrospective Study.

To explore whether tumor site, surgery type, and the different body mass index (BMI) of patients with breast cancer affect the positioning error. A retrospective study of 213 patients treated for breast cancer was binarily classified into groups based on the tumor site (left or right), surgery type (modified radical mastectomy, MRM and breast-conserving surgery, BCS) and BMI criterion (24 kg/m2). Positioning errors were obtained by using Cone-beam CT (CBCT) and analyzed to calculate the differences in 6 degrees of freedom. An independent sample t-test for positioning error was performed with a statistically significant level of 0.05. For tumor site, significant differences were observed in the X, Y, Rx, Ry, Rz directions. The t-test shows a significant difference in the X , Y and Z directions for translation errors of different surgery types. In terms of rotational errors, the Ry direction shows that the MRM group has significantly lower errors than the BCS group. Considering the influence of BMI, there is a significant difference in positioning errors only in the Z direction. For breast cancer patients, the Rz can serve as a reference for identifying positioning errors in other directions. For patients undergoing BCS, more individualized correction strategies during positioning are necessary. For obese patients, optimization measures should be implemented to address vertical positioning errors, considering body shape and size changes during treatment.