Bridging Beams and Arcs: Dosimetric and Workflow Evaluation of a Hybrid 3DCRT–VMAT Technique for Whole Breast Radiotherapy
Abstract
Purpose
To evaluate a hybrid radiotherapy planning technique combining conventional 3D conformal tangential fields with limited VMAT arcs (hybrid 3DCRT–VMAT) for whole‑breast irradiation, and compare its dosimetric performance, organ-at-risk sparing, and resource efficiency against standard 3DCRT and partial‑arc VMAT plans.
Methods
Thirty retrospective CT datasets of early-stage left-sided breast cancer patients were analyzed. For each patient, three plans were generated: standard tangential 3DCRT, partial-arc VMAT, and a hybrid 3DCRT–VMAT plan delivering 70% of the prescription dose via 3DCRT tangents and 30% via two partial VMAT arcs. All plans were normalized to the same prescription dose and optimized using identical target and OAR constraints. Dosimetric evaluation included PTV coverage (V95%, Dmean, Dmax), homogeneity index (HI), conformity index (CI), and doses to the heart, ipsilateral lung, and contralateral breast. Monitor units (MU), planning time, and estimated delivery time were also assessed. Statistical analysis was performed using paired Wilcoxon signed-rank tests (p < 0.05).
Results
All techniques achieved adequate PTV coverage (V95% ≥ 95%). Hybrid plans demonstrated significantly improved conformity compared to 3DCRT (CI = 1.18 ± 0.09 vs. 2.10 ± 0.45, p < 0.001) and were comparable to VMAT. Dose homogeneity was improved relative to 3DCRT and similar to VMAT. Hybrid 3DCRT–VMAT reduced mean heart dose by approximately 25% compared to VMAT (p < 0.01) and significantly decreased ipsilateral lung V5Gy and V20Gy, while limiting low-dose spread. Compared to 3DCRT, modest improvements in contralateral breast and lung sparing were observed. Hybrid plans required about 20% fewer MUs than VMAT, with only a modest (~10%) increase in planning time and comparable delivery times.
Conclusion
The hybrid 3DCRT–VMAT technique offers a balanced approach, combining improved target conformity and OAR sparing with efficient resource utilization, making it a promising option for whole breast radiotherapy.