Cardiac dosimetry of deep inspiration breath-hold technique in whole breast irradiation for left breast cancer after breast-conserving surgery

Objective: To study the effect of deep inspiration breath-hold (DIBH) technique on the heart dose in whole breast irradiation (WBI) for left breast cancer after breast-conserving surgery, and to investigate the anatomical factors for heart dose. Methods: Fifteen patients with left breast cancer who received WBI after breast-conserving surgery and met breathing control requirements were prospectively enrolled as subjects. Simulated CT scans were performed during free breathing (FB) and DIBH. The WBI plans were optimized based on DIBH images. The position, volume, and radiation doses to the heart and lung were compared between the status of FB and DIBH. Correlation of heart dose with various anatomical factors was analyzed in FB status. Between-group comparison of categorical data was made by nonparametric Wilcoxon rank test. A two-variable correlation analysis was made by the Pearson method. Results: There was no significant difference in heart volume between the status of FB and DIBH (P = 0.773). The volume of both lungs was significantly larger in DIBH status than in FB status (P = 0.001). The mean and maximum doses and V₅-V₄₀ for the heart, left anterior descending coronary artery, left ventricle, right ventricle, and left lung were significantly lower in DIBH status than in FB status (all P < 0.05). The greater DIBH increased the lung volume, the greater the mean heart dose decreased. In FB status, the left breast volume, heart-to-lung volume ratio, distance between the inferior margins of breast and heart, and maximum heart margin distance showed a linear correlation with heart dose. Particularly, the heart-to-lung volume ratio and maximum heart margin distance were independently correlated with heart dose. Conclusions: DIBH technique in WBI for left breast cancer after breast-conserving surgery significantly reduces heart and lung doses compared with FB. Changes in lung volume are the basis for improving the relative anatomical location of the heart. The heart-to-lung volume ratio and maximum heart margin distance may provide a reference for DIBH technique. (authors)