Cardiac Radiation Dose and Subclinical Coronary Artery Disease Progression after Breast Cancer Radiotherapy: 2-year Cardiac CT Results from the EARLY-HEART Study.

Purpose To evaluate the relationship between cardiac radiation dose and progression of subclinical coronary artery disease using cardiac CT at baseline and 24 months after breast cancer radiation therapy. Materials and Methods This secondary analysis of the prospective multicenter EARLY-HEART study (ClinicalTrials.gov identifier: NCT03297346) included asymptomatic participants with breast cancer treated with radiation therapy after lumpectomy who underwent cardiac CT before radiation therapy (T0) and at 24-month follow-up (T24). Cardiac radiation dose to the whole heart, left ventricle, right ventricle, and left anterior descending coronary artery was quantified using mean dose and volume-based metrics. Coronary artery calcium (CAC) progression was assessed as changes in CAC score between T0 and T24 at noncontrast CT, and stenosis progression was assessed at coronary CT angiography using Coronary Artery Disease Reporting and Data System classification. Associations between cardiac radiation dose and imaging-based progression were evaluated using multivariable linear and logistic regression models adjusted for cardiovascular risk factors. Results The final analysis included 224 participants (58.4 years ± 8.0; all female participants). CACS was higher at T24 than at T0 (median, 0 [IQR, 0-25] vs 0 [IQR, 0-17]; P < .001). Among 88 participants with CAC scores greater than 0 at T24, CACS increased more from T0 in the highest quartile of cardiac radiation dose compared with the remaining participants (whole heart mean dose, P < .001). The proportion of participants with CAC progression above the cohort median (16 participants) was also greater in those receiving the highest radiation doses (relative risk: whole heart, 2.0 [95% CI: 1.5, 2.8]; left ventricle, 1.8 [95% CI: 1.2, 2.5]; right ventricle, 1.7 [95% CI: 1.2, 2.5]; left anterior descending coronary artery, 1.5 [95% CI: 1.0, 2.3]). In contrast, progression of coronary stenosis at coronary CT angiography (36 of 224) was not associated with cardiac radiation dose but was strongly associated with higher baseline CACS and greater CAC progression (both P < .001). Conclusion Higher cardiac radiation dose during breast cancer radiation therapy was associated with increased CAC progression at 2-year follow-up, particularly in participants with preexisting calcification, whereas coronary stenosis progression was unrelated to dose. Keywords: Radiotherapy, Cardiac CT, Atherosclerosis, Coronary Artery Plaque Supplemental material is available for this article. ClinicalTrials.gov identifier: NCT03297346 © RSNA, 2026.