Heart and Left Anterior Descending Coronary Artery (LAD) Exposure from Hypo-Fractionated Whole Breast Radiotherapy with a Prone Set Up.

To describe left anterior descending coronary artery (LAD) and heart dosimetry in patients with left-side breast cancer undergoing adjuvant hypo-fractionated whole breast irradiation with a concomitant boost with a dedicated prone position cardiac-sparing protocol. In a consecutive series of 524 women, LAD and heart doses were reviewed from their radiation treatment plans retrospectively. For all patients, the setup was in the prone position and the medial edge of the breast tangents was placed at least 2.5 mm from the contoured LAD. A descriptive variables statistical analysis was performed. The Spearman's coefficients and linear regression models were applied to explore correlations between LAD and heart doses with breast and boost volumes. For LAD dosimetry, the mean values for Dmean, Dmax, and D2% were 2.20 Gy, 4.44 Gy, 3.57 Gy, respectively. For heart dosimetry, the mean values for Dmean, Dmax and D2% were 0.69 Gy, 7.92 Gy, 2.35 Gy, respectively. The mean volumes for PTV-breast and PTV-boost were 699.6 cc and 110.8 cc, respectively. No correlations were found among the cardiac dosimetry indices and breast/boost volumes. A linear relationship was found between Heart D2% and LAD Dmean, LAD D2% and LAD Dmax. A constraint of maintaining the Heart D2% dose less than 3 Gy achieved a LAD Dmean, LAD D2% and LAD Dmax less than 2.77, 4.36 and 5.16 Gy, respectively. A dedicated prone position cardiac-sparing protocol for hypo-fractionated breast irradiation minimizes LAD and heart exposure, regardless of individual body conformation and treatment volumes. The approach results in dosimetry superior or equivalent to that of more complex and costly radiotherapy techniques. Keeping the medial edge of the breast tangents at least 2.5 mm from the contoured LAD while limiting Heart D2% dose to <3 Gy will best prevent long term radiation associated cardiotoxicity. [ABSTRACT FROM AUTHOR]