Radiation-Induced Acute Cardiac Injury in Patients With Left-Sided Breast Cancer: A Cardiac Magnetic Resonance Study on the Dose-Response Relation.

[PURPOSE] Radiation therapy (RT) for breast cancer (BC) increases long-term cardiovascular risk; however, the early identification of acute cardiac injury remains critically underexplored. This study aimed to prospectively assess radiation-induced acute cardiac injury after postoperative left-sided BC RT using cardiac magnetic resonance (CMR) strain analysis.

[METHODS AND MATERIALS] Patients with left-sided BC undergoing RT were prospectively enrolled. Radiation doses to cardiac structures were calculated. CMR scans were performed within 2 weeks before and after RT.

[RESULTS] Among 64 enrolled patients, 41 received whole-breast RT (40.5 Gy/15 fractions; whole-breast RT [WBRT] group) and 23 received chest wall plus nodal RT (50 Gy/25 fractions; chest wall RT [CWRT] group). The mean cardiac dose in the CWRT group was higher than that in the WBRT group (mean heart dose [MHD]: 8.93 ± 2.67 Gy vs 2.80 [2.25 to 3.61] Gy, P < .001; left ventricle [LV]: 9.50 ± 3.49 Gy vs 2.85 [2.06 to 3.86] Gy, P < .001). The CWRT group demonstrated an increasing gradient of radiation dose from the basal to apical LV layers and a significant reduction in global longitudinal strain (GLS) (-17.50 [-15.73 to -17.85]% vs -15.32% ± 2.58%; P = .020) and global circumferential strain (GCS) (-20.34% ± 1.89% vs -19.22% ± 2.14%; P < .001) after RT, with similar alterations in the apical and middle layers, whereas the WBRT group showed no such changes. Among all patients, cardiac dosimetric parameters were independently associated with decreases in GLS and GCS (P < .05). Moreover, 10 patients (15.6%) developed cancer therapy-related cardiac dysfunction after RT; the combination of cardiac dose and the Systematic Coronary Risk Evaluation 2 risk index accurately predicted cancer therapy-related cardiac dysfunction (area under the curve, [AUC] = 0.931; AUC = 0.925).

[CONCLUSIONS] High-dose radiation exposure increases susceptibility to acute cardiac injury after left-sided BC RT. CMR-derived myocardial strain is a sensitive indicator of radiation-related acute cardiac dysfunction.