Dose to the Left Anterior Descending Artery Correlates With Cardiac Events After Irradiation for Breast Cancer

Although global heart dose has been associated with late cardiac toxic effects in patients who received radiation therapy for breast cancer, data detailing the clinical significance of cardiac substructure dosimetry are limited. We investigated whether dose to the left anterior descending artery (LAD) correlates with adverse cardiac events.

We identified 375 consecutively treated female patients from 2012 to 2018 who received left-sided breast or chest wall irradiation (with or without regional nodal irradiation). Medical records were queried to identify cardiac events after radiation therapy. Mean and maximum LAD and heart doses (LAD D_mean, LAD D_max, heart D_mean, and heart D_max) were calculated and converted to 2-Gy equivalent doses (EQD₂). Univariate and multivariable Cox regression analyses were performed to determine association with cardiac toxic effects. Potential dose thresholds for each of the 4 dose parameters were identified by receiver operating characteristic (ROC) curve analysis, after which Kaplan-Meier analysis was performed to compare cardiac event-free survival based on these constraints.

Median follow-up time was 48 months. Thirty-six patients experienced a cardiac event, and 23 patients experienced a major cardiac event. On univariate and multivariable analyses, increased LAD D_mean, LAD D_max, and heart D_mean were associated with increased risk of any cardiac event and a major cardiac event. ROC curve analysis identified a threshold LAD D_mean EQD₂ of 2.8 Gy (area under the ROC curve, 0.69), above which the risk for any cardiac event was higher (P = .001). Similar results were seen when stratifying by LAD D_max EQD₂ of 6.7 Gy (P = .005) and heart D_mean EQD₂ of 0.8 Gy (P = .01).

Dose to the LAD correlated with adverse cardiac events in this cohort. Contouring and minimizing dose to the LAD should be considered for patients receiving radiation therapy for left-sided breast cancer.