Cardiac MRI–based Subclinical Cardiac Dysfunction during 2 Years after Breast Cancer Irradiation: The MEDIRAD EARLY-HEART Study

Purpose To evaluate the relationship between cardiac radiation doses and subclinical changes in cardiac function using cardiac MRI during 2 years of follow-up in patients with breast cancer treated with radiation therapy without chemotherapy after lumpectomy. Materials and Methods This prospective multicenter study (NCT03297346) enrolled female individuals with breast cancer treated with radiation therapy between December 2017 and September 2019. Participants underwent cardiac MRI at baseline, 6 months, and 24 months. Cardiac radiation doses were assessed for the whole heart (WH) and right and left ventricles (LV). A persistent decrease in LV global longitudinal strain (GLS) from baseline to the other two measurement points over the 2-year follow-up was considered an adverse subclinical change in cardiac function. Statistical analysis included Wilcoxon tests for continuous variables and odds ratios for risk assessment. Results The study included 138 female participants (mean age, 58.4 years ± 8.0 [SD]). Mean WH and LV doses were 1.42 Gy (IQR, 1.03-2.01) and 1.46 Gy (IQR, 0.64-2.34). At the 2-year follow-up, all participants had reduced LV end-diastolic volume (EDV) (-4.0% ± 13.2; <i>P</i> < .001) and stroke volume (-3.4% ± 15.2; <i>P</i> < .001), preserved LV ejection fraction, and increased LV remodeling (LV mass/EDV ratio) (4.2% ± 18.1; <i>P</i> < .04) without associated symptoms. Twenty-three (16.6%) participants showed a persistent decrease in LV GLS and received higher mean WH and LV doses compared with participants without persistent decrease in LV GLS (WH: 2.09 Gy [IQR, 1.50-2.45] vs 1.36 Gy [IQR, 1.01-1.87], <i>P</i> < .001; LV: 2.40 Gy [IQR, 1.09-2.88] vs 1.34 Gy [IQR, 0.63-2.02], <i>P</i> = .002). The relative changes in LV EDV and LV mass/EDV were -12.7% ± 9.0 versus -2.2% ± 13.3 (<i>P</i> < .001) and 14.2% ± 15.5 versus 2.2% ± 18.1 (<i>P</i> = .002), respectively, in participants with and without a persistent decrease in LV GLS. A higher WH cardiac radiation dose was associated with a higher risk of a persistent decrease in LV GLS (odds ratio, 1.09 [95% CI: 1.02, 1.16]). Conclusion In participants with recent breast cancer radiation therapy, a modest but persistent reduction in LV GLS over a 2-year follow-up period was associated with the cardiac radiation dose. <b>Keywords:</b> Radiotherapy, Magnetic Resonance Imaging, Cardiotoxicity, Strain Clinical trial registration no. NCT03297346 <i>Supplemental material is available for this article.</i> © RSNA, 2025.