Regional Nodal Irradiation for Breast Cancer Using Volumetric Modulated Arc Therapy: Echocardiographic Functional Outcomes

Abstract

<h3>Purpose/Objective(s)</h3> Regional nodal irradiation (RNI) for breast cancer yields improvements in disease outcomes, yet comprehensive target coverage often increases cardiac radiation (RT) dose. Volumetric modulated arc therapy (VMAT) may mitigate high-dose cardiac exposure, although often increases the volume of low-dose exposure. The cardiac implications of this dosimetric configuration (in contrast to historic 3D conformal techniques) remains uncertain. <h3>Materials/Methods</h3> Eligible patients receiving adjuvant RNI using VMAT for locoregional breast cancer were prospectively enrolled on an IRB-approved study. Echocardiograms were performed prior to RT, at the conclusion of RT, and 6-months following RT. Echocardiographic parameters were measured by a single reader (AY) and measures were compared pre- and post-RT via the Wilcoxon signed rank test. Changes in echocardiographic parameters over time were compared to mean and max heart doses via the Spearman correlation test. <h3>Results</h3> Among 19 evaluable patients (median age 38), 89% (n=17) received doxorubicin and 37% (n=7) received trastuzumab/pertuzumab combination therapy. All patients received VMAT-based whole-breast/chest-wall and regional nodal irradiation. Average mean heart dose was 456cGy (range 187–697cGy) and average max heart dose was 3001cGy (1560-4793cGy). Among salient echocardiographic parameters, no significant decrement in cardiac function was observed when comparing pre-RT to 6-months post-RT: mean left ventricular ejection fraction (LVEF) was 61.8 (SD 4.4) pre-RT and 62.7 (SD 3.8) 6-months post-RT (p=0.493); mean global longitudinal strain (GLS) was -19.3 (SD 2.2) pre-RT and -19.6 (SD 1.8) 6-months post-RT (p=0.627). No correlations were observed for changes in LVEF or GLS when compared to mean or maximum heart doses (p>0.1 for all). <h3>Conclusion</h3> VMAT for left-sided RNI yielded no significant early decrement in echocardiographic parameters of cardiac function including LVEF and GLS. VMAT appears safe for patients requiring RNI, including those receiving anthracyclines and HER2-directed therapy. Larger cohorts with longer follow-up will be needed to validate these findings.