2754 - Cardiac Dose and Injury after Radiotherapy in Patients with Postoperative Left-Sided Breast Cancer: A Cardiac Magnetic Resonance Study

L. Zheng¹, C. Luo¹, X. Lv¹, M. Yang², Y. Li¹, K. Xu¹, K. Yuan¹, J. Xu³, J. Li³, J. Zhang³, H. Wang³, P. Zhou², J. Lang¹, and J. Yin¹; ¹Department of Radiation Oncology, Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, University of Electronic Science and Technology of China, chengdu, China, ²Department of Radiology, Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, University of Electronic Science and Technology of China, chengdu, China, ³Breast Surgery Center, Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, University of Electronic Science and Technology of China, chengdu, China

Purpose/Objective(s): Due to the increased survival of breast cancer, radiation-induced cardiac injury has received a growing focus. Early identification of acute cardiac injury helps improve the long-term prognosis of patients. Non-invasive cardiac magnetic resonance (CMR) is the imaging gold standard for cardiac function assessment and myocardial pathological changes. In particular, CMR strain analysis allows the sensitive assessment of subclinical cardiac motor dysfunction. Therefore, this study aims to evaluate the radiation-related acute subclinical cardiac injury for postoperative left-sided breast cancer using CMR prospectively. Materials/

Methods: Patients treated with postoperative adjuvant radiotherapy (RT) for left-sided breast cancer were prospectively enrolled. The whole heart was contoured, and the mean heart dose (MHD) was calculated. CMR scans were performed within two weeks before and after RT. CMR scan consists of cardiac cine and T2-weighted imaging to evaluate left ventricular ejection fraction (LVEF), global radial strain (GRS), global circumferential strain (GCS), global longitudinal strain (GLS), and myocardial edema, respectively. Cardiac injury was defined as the decrease of LVEF or global strain, or the occurrence of myocardial edema. Continuous variables were expressed as mean ± SD or median (interquartile range), as appropriate. The cardiac parameters between pre- and post-RT were compared using t-test or rank sum test, as appropriate. Linear regression models were used for multivariate analysis.
Results: 42 women patients aged 47 ± 10 years were enrolled. 24 patients received whole breast RT (40.5 Gy/15 Fx, whole breast group), and 18 patients received chest wall + nodal RT (50 Gy/25 Fx, chest-wall group). The MHD of the whole group was 4.65 (2.87, 8.84) Gy; and the MHD of the chest-wall group was higher compared with that of the whole breast group (8.79 ± 2.59 Gy vs. 3.29 ± 1.14 Gy, P<0.001). After RT, LVEF showed no significant changes, but myocardial edema was observed in nine patients in the whole group. Compared with baseline scan, a decrease of GLS [-17.01 ± 1.98% vs. -15.84 (-15.12, -17.50) %, P = 0.012] and GRS [34.73 (28.61, 38.90) % vs. 32.75 ± 6.23 %, P=0.010] was observed in the whole group after RT; in the whole breast group, GLS [-16.76 ± 2.38 % vs. -15.57 (-14.87, -16.63) %, P = 0.024] decreased, but there was no difference in GRS; in the chest-wall group, GRS decreased (35.13 ± 7.94 % vs. 31.65 ± 6.18 %, P=0.034), while no difference of GLS was shown. Multivariate analysis showed that chemotherapy is related to the changes in GLS, and high heart radiation dose is related to the changes in GRS.
Conclusion: Left-sided breast cancer RT could cause acute subclinical cardiac injury, manifested by a decrease in the left ventricular global strain. CMR strain allows the sensitive detection of acute cardiac injury soon after RT. A larger sample size with longer follow-up is needed in the future to further verify the prognostic value of cardiac strain decrease after RT.