Increased Number of Beam Angles Is Associated With Higher Cardiac Dose in Adjuvant Fixed Gantry Intensity Modulated Radiation Therapy of Left-Sided Breast Cancer

Purpose: To analyze the relationship between angle number and mean heart dose (MHD) in adjuvant fixed gantry intensity modulated radiation therapy (FG-IMRT) treatment of left-sided breast cancer as is currently practiced in the community. Methods and Materials: We performed a retrospective, multi-institutional review of women with left-sided breast cancer receiving adjuvant FG-IMRT between 2012 and 2014, encompassing 85 centers in 15 states. Bivariate and multivariate regression analyses were done to identify factors associated with MHD. Long-term cardiac risk was estimated according to a previously published model. Results: Of the 538 women included, 284 had >2 gantry angle treatment plans (multi-angle), and 254 had 2 gantry angle (standard) plans. Median MHD was higher in patients with multi-angle plans compared with standard (median 475 vs 203 cGy). Number of gantry angles was significantly associated with MHD, with multi-angle plans independently increasing MHD by 229 cGy. Absolute risk of acute coronary events 20 years after treatment was estimated as 7 excess events per 1000 women for standard plans, compared with 12 excess events for multiangle plans. Conclusions: Fixed gantry IMRT breast treatment plans with > 2 gantry angles were associated with increased MHD, which translated to an increased cardiac risk. Clinicians should account for this potential drawback in treatment technique when assessing overall plan quality. (C) 2017 Elsevier Inc. All rights reserved.