Purpose: Patients with Her2-positive breast cancer treated with trastuzumab have higher rates of cardiotoxicity (CT). Left-breast radiation might increase the risk for CT from cardiac exposure to radiation. The goal of our study is to evaluate the contribution of radiotherapy (RT) in the development of CT in breast cancer patients receiving trastuzumab.
Methods: Two hundred and two patients were treated with RT and trastuzumab from 2000 to 2014. The RT plans for left-side disease were recalled from archives. The heart, each chamber, and left anterior descending artery (LAD) were independently contoured. New dose-volume histograms (DVH) were generated. Their serial left-ventricular ejection fractions (LVEF) were studied. CT for left and right side were compared using Fisher's exact test. The DVH data were correlated with the predefined cardiac events using actuarial Cox regression analysis.
Results: Compared to the right sided, the left-side cases showed statistically significant development of arrhythmia (14.2%) versus (< 1%) (p < 0.001). Cardiac ischemia was found in 10 patients in left and one patient in right side (p = 0.011). The equivalent uniform dose (EUD) to the left ventricle (LV), right ventricle (RV), and LAD was significantly associated with decrease in LVEF by > 10% (p = 0.037, p = 0.023 and p = 0.049, respectively).
Conclusions: Among patients treated for left-sided lesions, there were no significant differences in EF decline. However, there was a higher rate of ischemia and arrhythmia compared to those with right-sided disease. The EUD index of LV, RV, and LAD could be considered as a parameter to describe the risk of radiation-induced CT.
Keywords: Cardiotoxicity; Dose-volume histograms; Radiotherapy; Trastuzumab.