Reduced lung dose during radiotherapy for thoracic esophageal carcinoma: VMAT combined with active breathing control for moderate DIBH

Background: Lung radiation injury is a critical complication of radiotherapy (RT) for thoracic esophageal carcinoma (EC). Therefore, the goal of this study was to investigate the feasibility and dosimetric effects of reducing the lung tissue irradiation dose during RT for thoracic EC by applying volumetric modulated arc radiotherapy (VMAT) combined with active breathing control (ABC) for moderate deep inspiration breath-hold (mDIBH). Methods: Fifteen patients with thoracic EC were randomly selected to undergo two series of computed tomography (CT) simulation scans with ABC used to achieve mDIBH (representing 80% of peak DIBH value) versus free breathing (FB). Gross tumor volumes were contoured on different CT images, and planning target volumes (PTVs) were obtained using different margins. For PTV-FB, intensity-modulated radiotherapy (IMRT) was designed with seven fields, and VMAT included two whole arcs. For PTV-DIBH, VMAT with three 135 degrees arcs was applied, and the corresponding plans were named: IMRT-FB, VMAT(-FB), and VMAT(-DIBH), respectively. Dosimetric differences between the different plans were compared. Results: The heart volumes decreased by 19.85%, while total lung volume increased by 52.54% in mDIBH, compared to FB (p < 0.05). The mean conformality index values and homogeneity index values for VMAT(-DIBH) (0.86, 1.07) were slightly worse than those for IMRT-FB (0.90, 1.05) and VMAT(-FB) (0.90, 1.06) (p > 0.05). Furthermore, compared to IMRT-FB and VMAT(-FB), VMAT(-DIBH) reduced the mean total lung dose by 18.64% and 17.84%, respectively (p < 0.05); moreover, the V-5, V-10, V-20, and V-30 values for IMRT-FB and VMAT(-FB) were reduced by 10.84% and 10.65% (p > 0.05), 12.5% and 20% (p < 0.05), 30.77% and 33.33% (p < 0.05), and 50.33% and 49.15% (p < 0.05), respectively. However, the heart dose-volume indices were similar between VMAT(-DIBH) and VMAT(-FB) which were lower than IMRT-FB without being statistically significant (p > 0.05). The monitor units and treatment time of VMAT(-DIBH) were also the lowest (p < 0.05). Conclusions: VMAT combined with ABC to achieve mDIBH is a feasible approach for RT of thoracic EC. Furthermore, this method has the potential to effectively reduce lung dose in a shorter treatment time and with better targeting accuracy.