Background: Radiotherapy (RT) for breast cancer (BC) can induce coronary artery disease many years after RT. At an earlier stage, during the first two years after RT, we aimed to evaluate the occurrence of increased coronary artery calcium (CAC) and its association with cardiac exposure. Methods: This prospective study included 101 BC patients treated with RT without chemotherapy. Based on CAC CT scans performed before and two years after RT, the event ‘CAC progression’ was defined by an increase in overall CAC score (CAC RT+ two years—CAC before RT > 0). Dosimetry was evaluated for whole heart, left ventricle (LV), and coronary arteries. Multivariable logistic regression models were used to assess association with doses. Results: Two years after RT, 28 patients presented the event ‘CAC progression’, explained in 93% of cases by a higher CAC score in the left anterior descending coronary (LAD). A dose–response relationship was observed with LV exposure (for Dmean LV: OR = 1.15, p = 0.04). LAD exposure marginally explained increased CAC in the LAD (for D2 LV: OR =1.03, p = 0.07). Conclusion: The risk of early CAC progression may be associated with LV exposure. This progression might primarily be a consequence of CAC increase in the LAD and its exposure.

Background—Radiotherapy (RT) for breast cancer (BC) can lead to an increased risk of coronary artery disease several years after RT. The aim of this study was to evaluate the development of overall, non-calcified and calcified atherosclerotic plaques over 2 years after BC for RT and associations with cardiac exposure. Methods—The study included 101 left- or right-sided BC patients treated with RT without chemotherapy. A coronary CT angiography was performed before and 2 years after RT. Plaque development thorough the entire coronary network was defined as an increased number of plaques. Cardiac exposure was quantified with mean doses to the heart, left ventricle, and coronary arteries. Logistic regression models were used to assess association with doses. Results—At inclusion, 37% of patients had plaques, increasing to 42% two years after RT. Overall plaque development was observed in seven patients: five with calcified plaque development and four with non-calcified plaque development. The risk of overall plaque development was significantly associated with doses to the Left Main and Circumflex coronary arteries (OR at 1 Gy = 2.32, p = 0.03 and OR at 1 Gy = 2.27, p = 0.03, respectively). Specific analyses for calcified and non-calcified plaque development showed similar results. Conclusion—Our study suggests an association between coronary arteries exposure and the risk of developing both calcified and non-calcified atherosclerotic plaques over 2 years after BC RT. Trial registration number: NCT02605512.