Radiation-induced risk of ischemic heart disease following breast cancer radiotherapy in Denmark, 1977-2005

Background and purpose: The increase in the risk of heart disease from incidental exposure of the heart during radiotherapy for breast cancer has been estimated previously from retrospective data in Danish and Swedish women. Here we present an analysis of the Danish material updated with new cases and controls, extended follow-up period, and with refined dose estimates using simulator films or CT data. Material and methods: From the database of the Danish Breast Cancer Cooperative Group, we identified 531 women diagnosed with early-stage breast cancer from 1977 to 2005, who developed subsequent ischemic heart disease (cases) and matched them to 1069 controls without heart disease after radiotherapy. Data were available for precise dose estimation for 196 cases and 413 controls receiving tangential photon techniques. Results: The median of the mean heart doses for the women receiving tangential radiotherapy was 2.41 Gy for left- and 0.68 Gy for right-sided radiotherapy. The mean heart dose was higher for cases than controls (0.84 Gy and 0.71 Gy, respectively; p < 0.001). In this group, the linear increase in the excess odds ratio of major coronary events per gray of mean heart dose (K) was 19 percent (95% Confidence Interval (CI) 1% to 63%, p = 0.02). For patients treated with electron techniques, there was no significant association between mean heart dose and the risk of major coronary events (K = -0.05, 95% CI-12% to 9%, p = 1.00). Conclusion: The increase in the excess odds of major coronary events per gray mean heart dose using individual dose estimates is higher than previously reported. (C) 2020 Elsevier B.V. All rights reserved.