The Impact of Tumor Location on Cardiac Toxicity in Patients Receiving Partial Breast Irradiation

Abstract

Accelerated partial breast irradiation (APBI) is an appropriate modality for select women with low-risk breast cancer. While APBI delivers radiation dose to a smaller volume of breast tissue compared to whole breast irradiation, dose to the heart and coronary vessels may be relatively high, depending on the proximity of the tumor bed to these structures. The purpose of this study is to determine if there is a correlation between tumor location and risk of adverse cardiac events in women receiving APBI. This retrospective study included 341 women who received ABPI from 1993 to February 2017 at a single institution. APBI was delivered by catheter-based high-dose-rate (HDR) brachytherapy via single lumen or multi-channel devices (n = 340), or external beam brachytherapy (n = 1). Neither the heart nor cardiac substructures were contoured for patients receiving APBI with HDR brachytherapy. Univariate analysis (UVA) and multivariable analysis (MVA) were conducted to correlate patient age, smoking status, Charlson Comorbidity Index score (CCI), receipt of systemic therapy, and tumor location (right outer, right inner/central, left outer, left inner/central) with subsequent cardiac events. Univariate analyses for patient age, smoking status, CCI, receipt of systemic therapy, and tumor location in correlation to subsequent cardiac events were performed. On UVA, age at diagnosis and CCI score ≥2 were both significant with HR of 1.07 [1.05-1.10] (p<0.001) and HR of 7.02 [3.22-15.3] (p<0.001), respectively. On MVA, age at diagnosis and CCI score ≥2 remained significant with HR of 1.06 [1.03-1.09] (p = <0.001) and HR of 4.56 [2.02-10.40] (p = <0.001), respectively. There was a trend of statistically significant correlation between cardiac events and left inner/central tumor location when compared to right outer tumor location with a HR of 2.06 [1.00,4.24] (p = 0.05). Treatment of tumor beds located in the inner/central portion of the left breast may increase the risk of developing cardiac toxicity in patients receiving APBI. These data support careful contouring and avoidance of cardiac structures during APBI treatment planning, including HDR brachytherapy.