Cross-sectional study of cardiac risk after heart-sparing radiotherapy for breast cancer

Radiotherapy for breast cancer exposes the heart to incidental radiation, and historical data have shown a dose-dependent increase in associated cardiac events. Although whole-heart dose metrics are commonly used for risk assessment, emerging evidence suggests that dose to the left anterior descending coronary artery (LAD) may better capture risk. A cross-sectional study of breast cancer patients at a tertiary care in Calgary (Alberta, Canada) compared the ability of whole-heart and LAD radiation dose metrics to predict cardiac risk after breast 3-D conformal or intensity modulated radiotherapy. The analysis included 4908 patients with breast cancer of whom 2223 had left-sided breast cancer. During a median follow-up of 10.8 years (IQR 8.4-13.1), cumulative incidence of cardiac events including coronary artery disease was 5.0 (95% CI 4.1-6.0) at 10 years. Among patients with left-sided breast cancer, maximum LAD dose (C index 0.58; 95% CI -0.52-0.64) discriminated better than mean heart dose (0.53; 0.47-0.60). In multivariable analysis, higher maximum LAD dose had a statistically significant independent association with increased risk of cardiac events, whereas whole-heart dose did not. The authors conclude that these findings suggest that LAD-specific dosimetry may better identify cardiac risk than whole-heart metrics in modern breast radiotherapy.