Optimizing Left-Sided Breast Cancer Radiotherapy: Strategy-Dependent Trade-Offs Among VMAT and Hybrid Techniques

Purpose: To compare dosimetric trade-offs among two full-VMAT and two hybrid 3D-CRT/VMAT strategies for left-sided whole-breast irradiation (WBI), and to evaluate the influence of planning strategy, introducing a novel tangential hybrid approach (H-tVMAT). Patients and Methods: Twenty patients with left-sided breast cancer treated with WBI (40.05 Gy in 15 fractions) were retrospectively analyzed. For each patient, four plans were generated within a single treatment planning system under free-breathing conditions: large-angle VMAT, tangential VMAT (tVMAT), Hybrid VMAT (H-VMAT), and the novel tangential Hybrid tVMAT (H-tVMAT). Primary dosimetric endpoints included heart and pulmonary structures and the contralateral breast, with dedicated evaluation of low-dose exposure. Target conformity, homogeneity index (HI), and monitor units (MUs) were also assessed. Results: All strategies achieved clinically acceptable target coverage and homogeneity. Hybrid configurations consistently reduced cardiac, pulmonary, and contralateral low-dose exposure compared with full-VMAT solutions. Among the evaluated strategies, H-tVMAT provided the most favorable balance between heart/LAD sparing, low-dose containment, and target coverage. Appropriately configured tangential VMAT achieved dosimetric results close to hybrid solutions, underscoring the importance of arc geometry. No statistically significant differences in delivery complexity were observed across strategies. Conclusion: Dosimetric performance in left-sided WBI is strongly influenced by planning implementation rather than nominal technique category alone. Hybrid tangential VMAT achieved the most balanced dosimetric profile, while optimized tangential VMAT provided comparable results. These findings support a strategy-specific approach to technique selection, emphasizing the central role of implementation choices in breast radiotherapy planning.