Modeled risk of ischemic heart disease following left breast irradiation with deep inspiration breath hold

Purpose: Deep inspiration breath hold (DIBH) dramatically reduces radiation dose to the heart during radiation therapy (RT) for left-sided breast cancer, but the subsequent risk of radiation-related ischemic heart disease (IHD) is unknown. Our primary objective was to quantify the risk of IHD following RT with DIBH using modeled risk estimates (MRE). Methods and materials: Patients with stage 0-III left-sided breast cancer who received RT with DIBH were retrospectively studied. Computed tomography simulations were performed with DIBH and during free breathing (FB) for comparison of dosimetry. Patientswere classified as high risk, at risk, or at optimal risk for IHD and baseline risk estimates for IHD were obtained from historic controls. The excess relative risk of IHD because of left breast RT was calculated using patient-specific dosimetry and an existing dose-effect model. MRE were determined from the sum of baseline risk estimates and excess risk. Results: Between 2002 and 2011, 111 patients were treated using DIBH and 104 were available for analysis. MRE for 10-year risk of IHD with DIBH and FB were 3.25% (interquartile range [IQR], 1.20-3.44) and 3.64% (IQR, 1.43-3.81) (P < .0001), respectively. MRE for lifetime risk of IHD with DIBH and FB were 9.71% (IQR, 1.98-16.62) and 10.28% (IQR, 2.05-16.97) (P < .0001), respectively. MRE were significantly reduced by use of DIBH in all risk groups. The largest absolute risk reduction resulting from the DIBH technique was observed in patients at high risk for IHD. The median relative risk reduction in MRE resulting from DIBH was 11.4% (range, 0-32.0) and 6.4% (range, 0-23.4) at 10 years and throughout the patients' lifetime, respectively. After a median follow-up of 7.0 years (range, 1.3-11.2), the estimated 10-year freedom from IHD was 99.0% (95% confidence interval 93.4-99.8). Conclusions: RT with DIBH may provide breast cancer survivors a clinically significant reduction in the risk of IHD. (C) 2015 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.