Size Matters: Predicting Surgical Site Infection After Whole Breast Radiotherapy in the Era of Hypofractionation

<b>Objectives</b>: Few studies have analyzed surgical site infections associated with hypofractionated RT. The purpose of this study was to identify risk factors for surgical site infections with a particular focus on volumetric parameters that reflect the size of the volumes treated, including tumors, surgical cavities, and breasts. <b>Methods</b>: A total of 145 early breast cancer patients who were surgically staged 0-II undergoing hypofractionated RT on the whole breast were retrospectively reviewed. Tumor size (cm) was measured from surgical pathology. Surgical cavity volume (cc) and breast volume (cc) were calculated by segmenting each axial slice of simulation CT. The cavity-to-breast ratio (%) was calculated as surgical cavity volume/breast volume × 100. <b>Results</b>: The incidence of surgical site infection was 4.8% at a median of 6.3 months after the completion of RT. In univariate analysis, tumor size (OR 2.01, <i>p</i> = 0.025), surgical cavity volume (OR 1.03, <i>p</i> = 0.013), cavity-to-breast ratio (OR 1.29, <i>p</i> = 0.005), and BMI (OR 1.23, <i>p</i> = 0.014) were significantly associated with surgical site infection. In multivariate analysis, the cavity-to-breast ratio (OR 1.24, <i>p</i> = 0.039) remained significantly associated with surgical site infection. <b>Conclusions</b>: This study highlights the importance of volumetric parameters, specifically the cavity-to-breast ratio, as significant predictors of surgical site infection in a pure cohort of early breast cancer patients undergoing breast-conserving surgery and hypofractionated RT. Tailored approaches, including the use of prophylactic antibiotics, prophylactic aspiration, and close follow-up, may reduce the morbidity associated with surgical site infection and prevent the potential compromise of tumor outcomes.