Feasibility and trade-offs of incorporating cardiac substructure dose constraints in left-sided breast volumetric modulated arc therapy planning

Purpose: This study aimed to compare left-sided breast volumetric modulated arc therapy plans using heart-only dose constraints with plans that include additional left ventricle (LV) and left anterior descending coronary artery (LAD) dose constraints (heart + LV + LAD). Materials and Methods: Thirty patients treated with whole-breast irradiation with simultaneous integrated boost were replanned using both strategies. The heart + LV + LAD strategy applied dose constraints based on German Society for Radiation Oncology recommendations and Danish Breast Cancer Group HYPO protocol (LV: Dmean [mean dose] <3 Gy, V5Gy [percentage of volume receiving ≥5 Gy] <17%, V23Gy <5%; LAD: Dmean <10 Gy, Dmax [maximum dose] <17 Gy). Target and organ-at-risk (OAR) metrics were compared using Wilcoxon signed-rank tests. For exploratory analyses, LAD-planning target volume (PTV) distance was defined as the minimum distance between LAD and whole-breast PTV, and Spearman's correlations between LAD-PTV distance and LAD or target metrics were evaluated. Results: Compared with heart-only plans, heart + LV + LAD plans reduced LV Dmean, V5Gy, and V23Gy, as well as LAD Dmean and Dmax (all p < 0.001), meeting all prespecified dose constraints except LV Dmean and LAD Dmax (achieved in 70.0% and 63.3%, respectively). Target metrics showed small compromises (e.g., PTV V95% [percentage of volume receiving ≥95% of the prescription dose] 98.391% vs. 99.431%; p < 0.001). Ipsilateral lung Dmean and V5Gy decreased, whereas contralateral breast Dmean and lung V10Gy increased (all p < 0.05). In heart + LV + LAD plans, greater LAD-PTV distance correlated with lower LAD Dmax and Dmean and higher PTV D98%. Conclusion: Applying LV and LAD dose constraints improved cardiac substructure sparing with modest trade-offs in target and contralateral OAR metrics. LAD-PTV distance may influence the feasibility of LAD sparing, but this exploratory association warrants further study.