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

초록

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: D-mean [mean dose] <3 Gy, V-5Gy [percentage of volume receiving =5 Gy] <17%, V-23Gy <5%; LAD: D-mean <10 Gy, D-max [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 wholebreast 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 D-mean, V-5Gy, and V-23Gy, as well as LAD D-mean and D-max (all p < 0.001), meeting all prespecified dose constraints except LV D-mean and LAD D-max (achieved in 70.0% and 63.3%, respectively). Target metrics showed small compromises (e.g., PTV V-95% [percentage of volume receiving >= 95% of the prescription dose] 98.391% vs. 99.431%; p < 0.001). Ipsilateral lung D-mean and V-5Gy decreased, whereas contralateral breast D-mean and lung V-10Gy increased (all p < 0.05). In heart + LV + LAD plans, greater LAD-PTV distance correlated with lower LAD D-max and D-mean and higher PTV D-98%. 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.

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