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

Radiotherapy for left-sided breast cancer faces challenges in sparing cardiac structures due to anatomical proximity. Deep inspiration breath-hold (DIBH) and advanced techniques like VMAT offer potential solutions, but their synergistic effects on dose distribution and radiobiological outcomes require comprehensive evaluation. 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. 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). Dosimetric evaluation included Conformity Index (CI) and Homogeneity Index (HI) for targets alongside dose-volume parameters for OARs (heart, LAD, bilateral lungs) derived from Dose-volume histogram (DVHs). Radiobiological assessment employed: 1) Niemierko-based Tumor Control Probability (TCP), 2) Lyman-Kutcher-Burman Normal Tissue Complication Probability (NTCP) for cardiac/left lung tissues, and 3) linear model-derived Excess Absolute Risk (EAR) for contralateral breast. DIBH significantly increased left lung volume by 799.2 cm 3 ( 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). 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.