Abstract
Optimal cardiac dose constraints in breast cancer (BC) patients undergoing postoperative intensity-modulated radiation therapy (IMRT) are unclear, although as low as possible is recommended. This trial proposes serial cardiac dose constraint to optimize cardiac safety. Postoperative BC patients eligible for anthracycline/taxanes-based chemotherapy or HER2-targeted therapy were randomized to cardiac safety arm with prespecified mean heart dose (MHD) (≤6 Gy), V30 (≤20%), and V10 (≤50%) constraints, or to a control arm with in-house protocol (mainly MHD ≤8 Gy). The primary endpoint was cumulative incidence of newly onset cardiac events within 1-year post-RT. An exploratory analysis examined the relationship between whole heart dose metrics and those of substructures. Of 199 participants, 93 were in the cardiac safety and 106 in the control arm. The cardiac safety group showed lower MHD, V10, and V30. The 1-year cardiac event incidence was slightly lower in the cardiac safety group (19.4%) compared to controls (24.9%). The LVEF and diastolic dysfunction rates were 0% and 5.4% in the study arm, and 1.9% and 8.8% in the control arm, respectively. The LAD, LV, and RV received the highest doses for left-sided patients. For right-sided patients, RA, RCA, and RV were most irradiated. The MHD, V10, and Dmax of heart significantly correlated with all substructure doses in either laterality. Our study supports the early cardiac safety profile using IMRT in BC patients receiving cardiac-toxic systemic therapy, with serial cardiac dose constraints. Combined constraints on MHD and dose-volume parameters are representative of the cardiac substructure dose.