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Abstract Background Radiation therapy (RT) for breast cancer (BC) can result in subtle cardiac dysfunction that can occur early after treatment. In 2022, the European Society of Cardiology (ESC) published the first guidelines in cardio-oncology with a harmonized definition of cancer therapy-related cardiac dysfunction (CTRCD). The aim of this study was to evaluate CTRCD occurrence over 24 months of follow-up after RT in BC patients and to analyze the association with cardiac radiation exposure. Methods The prospective monocentric BACCARAT study included BC patients treated with RT without chemotherapy, aged 40–75 years, with conventional and 2D Speckle tracking echocardiography performed before RT, 6 and 24 months after RT. Based on ESC cardio-oncology guidelines, CTRCD and corresponding severity were defined with left ventricle ejection fraction and global longitudinal strain decrease, occurring at 6 or 24 months after RT. Dosimetry for whole heart, left ventricle (LV) and left coronary artery (left anterior descending and circumflex arteries (CX)) was considered to evaluate the association with CTRCD, based on logistic regressions (Odds Ratio – OR and 95% confidence interval – 95%CI). Youden index based on receiver operating characteristic curve analysis was used to identify the optimal threshold of dose-volume parameters for predicting CTRCD. Results The study included 72 BC patients with a mean age of 58 ± 8.2 years. A total of 32 (44%) patients developed CTRCD during follow-up: 20 (28%) mild CTRCD, 7 (9%) moderate CTRCD, and 5 (7%) severe CTRCD. Cardiac radiation doses were generally higher among patients with CTRCD rather than non-CTRCD. Dose-response relationships were significant for mean CX dose (OR = 2.48, 95%CI (1.12–5.51), p = 0.02) and marginally significant for V2 of LV (OR = 1.03 95%CI (1.00-1.06), p = 0.05). V2 of LV ≥ 36% and mean CX dose ≥ 1.40 Gy thresholds were determined to be optimal for predicting CTRCD. Conclusion For BC patients treated with RT without chemotherapy, CTRCD can be observed in an important proportion of the population over 24 months after treatment. Left ventricle and circumflex coronary artery exposure were found to be associated with CTRCD and could be used for the prediction of such cardiotoxicity. Further research remains needed to confirm these results. Trial Registration ClinicalTrials.gov Identifier- NCT02605512.

Purpose: To assess sinoatrial node (SAN) and atrioventricular node (AVN) doses for breast cancer (BC) patients treated with 3D-CRT and evaluate whether “large” cardiac structures (whole heart and four cardiac chambers) would be relevant surrogates. Material and methods: This single center study was based on 116 BCE patients (56 left-sided, 60 right-sided) treated with 3D-CRT without respiratory gating strategies and few IMN irradiations from 2009 to 2013. The heart, the left and right ventricles (LV, RV), the left and right atria (LA, RA) were contoured using multi-atlases for auto-segmentation. The SAN and the AVN were manually delineated using a specific atlas. Based on regression analysis, the coefficients of determination (R2) were estimated to evaluate whether “large” cardiac structures were relevant surrogates (R2 > 0.70) of SAN and AVN doses. Results: For left-sided BC, mean doses were: 3.60 ± 2.28 Gy for heart, 0.47 ± 0.24 Gy for SAN and 0.74 ± 0.29 Gy for AVN. For right-sided BC, mean heart dose was 0.60 ± 0.25 Gy, mean SAN dose was 1.57 ± 0.63 Gy (>85 % of patients with SAN doses > 1 Gy) and mean AVN dose was 0.51 ± 0.14 Gy. Among all “large” cardiac structures, RA appeared as the best surrogate for SAN doses (R2 > 0.80). Regarding AVN doses, the RA may also be an interesting surrogate for left-sided BC (R2 = 0.78), but none of “large” cardiac structures appeared as relevant surrogates among right-sided BC (all R2