Angular-optimized volumetric modulated arc therapy improves cardiac sparing and efficiency in early left-breast radiotherapy

Abstract

This dosimetric study evaluated angular-optimized volumetric modulated arc therapy (AO-VMAT) with non-opposed tangential beams and dynamic jaw tracking in 15 retrospective left-sided breast cancer patients. AO-VMAT comprised two non-opposed 180° arcs: start angles were set at 300° ± 5° and 130° ± 5° based on cardiac substructure geometry at the beam entrance, and stop angles were placed 180° apart to minimize heart and lung entry doses. For reference, angular-optimized intensity-modulated radiation therapy (AO-IMRT) using five non-opposed fixed beams was also generated, but the main comparison focused on AO-VMAT versus opposed-field VMAT (OF-VMAT). All techniques met clinical target coverage. Compared with OF-VMAT, AO-VMAT significantly reduced left anterior descending artery V 20 (43.08% ± 30.55% vs. 47.33% ± 29.55%, *p* = 0.013), left ventricle V 20 (5.35% ± 2.18% vs. 6.52% ± 2.86%, *p* = 0.020), and left ventricle mean dose (635.76 ± 102.07 cGy vs. 677.27 ± 103.38 cGy, *p* = 0.026). Left lung V 20 also decreased (15.11% ± 1.92% vs. 15.87% ± 1.89%, *p* = 0.020), and contralateral breast mean dose was lowered (378.62 ± 78.67 cGy vs. 408.99 ± 157.82 cGy, *p* = 0.021), albeit with a slight increase in low-dose lung V 5 (52.28% ± 6.94% vs. 49.26% ± 6.92%, *p* = 0.025). Treatment efficiency was comparable between AO-VMAT and OF-VMAT (monitor units: 896.47 ± 82.01 vs. 852.60 ± 58.91, *p* = 0.063; beam-on time: 105.87 ± 7.59 s vs. 110.80 ± 8.31 s, *p* = 0.103), and both were superior to AO-IMRT.Patient-specific QA passing rates were clinically acceptable for all techniques. These findings support AO-VMAT as an efficient cardiac-sparing option alongside OF-VMAT, without compromising deliverability.