Anatomic features of interest in women at risk of cardiac exposure from whole breast radiotherapy.

Abstract

Left-sided breast radiotherapy (RT) can result in cardiac exposure. This study aims to identify predictive anatomic features in women requiring breath-hold (RT(BH)) for cardiac sparing during adjuvant whole breast RT. We retrospectively reviewed free-breathing (FB) CT scans of 80 women previously treated with left-sided breast RT. Unfavourable cardiac anatomy was defined as the number of consecutive axial CT slices (2 mm) in which the anterior chest wall contacted the heart (Contact(Heart)) or left ventricle (Contact(LV)). The sternal angle and Haller Index (HI) were used to measure chest concavity. Position and volume of post-operative cavity was also quantified. Heart mean dose (D(mean)) was strongly correlated with Contact(LV) (r=0.625, p<0.001) and Contact(Heart) (r=0.524, p<0.001) but not significantly correlated with tumor size, cavity volume, heart volume, cavity distance to chest wall, sternal angle, or HI. ROC analysis of Contact(Heart) was most predictive of the need for breath-hold (RT(BH)) technique [Area Under Curve=0.815 (SE: 0.048; 95% CI: 0.721-0.91)] and ⩾25 Contact(Heart) CT slices predicted for heart D(mean) ⩾1.7 Gy (68% sensitivity and 82% specificity). Contact(Heart) on FB CT of ⩾25 axial slices (2 mm), ⩾50 mm of para-sagittal heart contact, was predictive of higher heart D(mean) and suggest a potential need for RT(BH).