Impact of Deep Inspiration Breath-Hold (DIBH) on Dose Distribution and Radiobiological Effects in Left-Sided Breast Irradiation: A Comparative Study of IMRT and VMAT Techniques Under DIBH and Free Breathing Conditions

Objective To compare the dosimetric and radiobiological differences between various radiotherapy techniques (VMAT vs. IMRT) under different respiratory modes (DIBH vs. FB) for left breast cancer patients after breast-conserving surgery. Methods This retrospective study analyzed 27 left breast cancer patients treated between May 2023 and October 2024. CT scans were acquired under both FB and DIBH conditions for each patient. Three half-beam radiotherapy plans were designed: D-IMRT (DIBH-IMRT), D-VMAT (DIBH-VMAT), and F-VMAT (FB-VMAT). Dose-volume histogram (DVH) parameters were evaluated for target coverage (Conformity Index [CI], Homogeneity Index [HI]) and organ-at-risk doses (heart, left anterior descending coronary artery [LAD], bilateral lungs). The Lyman-Kutcher-Burman model calculated normal tissue complication probabilities (NTCP) for heart/left lung, while a linear model estimated excess absolute risk (EAR) for contralateral breast irradiation. Results DIBH significantly increased left lung volume by 799.2 cm³ ( p  < 0.001) and heart-chest wall distance by 1.3 cm ( p  < 0.001). All plans achieved comparable target coverage and homogeneity. Compared with D-IMRT, D-VMAT demonstrated superior target conformity (PTV: 0.870 vs. 0.827; PTV_Bed: 0.775 vs. 0.757, p  < 0.05), reduced monitor units by 47.6% (618 vs. 1179, p  < 0.001), and significantly lowered cardiac doses (V5%: 5.82% vs. 11.83%; V20%: 0.16% vs. 0.58%; mean dose: 1.92 Gy vs. 2.57 Gy, p  < 0.05) with corresponding NTCP reduction (1.93E-11 vs. 6.61E-11, p  < 0.003). However, D-VMAT increased contralateral breast exposure (V5%: 5.60% vs. 1.72%; mean dose: 1.45 Gy vs. 0.71 Gy) and EAR (152.82 vs. 55.63, p  < 0.001). Compared with F-VMAT, D-VMAT further reduced cardiac doses (V5%: 5.82% vs. 13.27%; V20%: 0.16% vs. 5.2%; mean dose: 1.92 Gy vs. 3.83 Gy; NTCP: 1.93E-11 vs. 8.77E-11, p  < 0.001) and left lung V20% (11.15% vs. 13.43%, p  < 0.001). Conclusion DIBH-VMAT synergistically reduces cardiac and pulmonary radiation exposure while maintaining target coverage, albeit with increased contralateral breast dose. Clinical implementation requires careful risk-benefit assessment for personalized radiotherapy.