To determine if a patient’s breast size accurately correlates with the breast volume measured in the computed tomography (CT) scan, and to determine which sizes correspond to a volume >750 cc; in order to predict which patients will benefit from breast irradiation in the prone position.

Breast size was calculated as the difference between the thoracic (band) and breast (bust) circumferences. Breast volume was contoured by a radiation oncologist and measured on the simulation CT scan. Pearson’s coefficient was used to evaluate the correlation between both variables. A receiver operating characteristic (ROC) analysis was performed to determine the optimal cut-off point to predict which differences between band and bust would be associated with a volume ≥750 cc.

Fifty-nine patients were included in this study. Mean breast volume was 851·8 cc and mean size difference was 4·7 inches. Pearson’s correlation coefficient was 0·61 (p<0·001). The ROC analysis determined that a difference of 5 inches between the band and bust circumferences was the optimal cut-off point to determine a breast volume of 750 cc.

A significant correlation between breast size as measured in the clinical practice and breast volume measured in the CT scan was found. Among other characteristics, a 5-inch difference between breast band and bust will be the cut-off point to decide if a patient will be treated prone at our institution.