Study on the safety of simultaneous integrated boost and the importance of cardiac substructural dose assessment of hypofractionated radiotherapy after early left breast cancer breast-conserving surgery

Background and purpose: Adjuvant radiotherapy for breast cancer after early breast-conserving surgery has been recommended by the guidelines. However, the feasibility of hypofractionated radiotherapy with simultaneous integrated boost is not available. In this randomized controlled study, the cardiac dosimetry parameters and cardiac ultrasound indexes of the two radiotherapy plans were compared to evaluate the safety of hypofractionated radiotherapy with simultaneous integrated boost plan in terms of cardiotoxicity. Methods: A total of 40 patients with breast cancer who received breast-conserving surgery were selected in Zhongshan Hospital, Fudan University from March 2017 to March 2018. They were randomly divided into two groups, including 20 patients reveiving hypofractionated radiotherapy with simultaneous integrated boost plan (whole breast 4 005 cGy/15 Fx, tumor bed 4 500 cGy/15 Fx) and 20 patients reveiving conventional fractionation with simultaneous integrated boost plan (whole breast 5 000 cGy/25 Fx, tumor bed 6 000 cGy/25 Fx). The cardiac dosimetric parameters and cardiac ultrasound indexes of the two groups were compared. The dosimetric parameters included the average doses (Dmean) of the whole heart, left ventricle, right ventricle, right ventricular free wall, ventricular septum and left anterior descending (LAD) coronary artery, and the relative volume fraction of each structure irradiated by 5-35 Gy (V5 Gy-V35 Gy). The follow-up indexes of echocardiography included aortic root diameter, left atrial diameter, left ventricular end diastolic diameter, left ventricular end systolic diameter, ventricular septal thickness, left ventricular posterior wall thickness, pulmonary artery systolic pressure, left ventricular ejection fraction, E peak, A peak, E-peak deceleration time (DT), E, A, E/A and S wave peak. In addition, the cosmetic effect on breast after radiotherapy in the two groups was also evaluated. Results: Dmean of the whole heart in the hypofractionated group and the conventional group were (471.86±170.54) and (733.07±79.11) cGy (P