Optimizing stereotactic ablative body radiotherapy for ultra-central lung lesions: a comparative dosimetric analysis

Stereotactic ablative body radiotherapy (SABR) for ultra-central (UC) lung tumors is still challenging due to potentially severe complications caused by overdoses to critical mediastinal structures. This study aimed to compare the dosimetric advantages between volumetric modulated arc therapy (VMAT)-SABR and Helical Tomotherapy (HT)-SABR in UC lung lesions. From August 14, 2019, to June 4, 2023, patients with ultra-central (UC) lung tumors who received SABR for lung tumors were enrolled in this study. Two different radiotherapy plans were created based on the CT datasets of each case on the Eclipse and Tomotherapy treatment planning systems respectively. All patients received 60 Gy in 8 fractions. The parameters for dose evaluation of the target volumes and organs at risk (OARs) were compared based on the data extracted from dose-volume histograms. All of the statistical analyses were performed with SPSS 17.0 software. Compared with HT-SABR, VMAT-SABR significantly increased the Dmean of the iGTV (p = 0.002) and the Dmean, D10%, and D5% of the PTV (p = 0.000, 0.000, and 0.002, respectively). The values of D2cm, 95% isodose volume, and GI of VMAT-SABR significantly decreased by 15.11%, 7.78%, and 20.65% (p = 0.000; 0.000; 0.000) respectively. The values of Dmax of the spinal cord, spinal cord + 3 mm, esophagus, heart, trachea, proximal bronchial tree (Pbtree), and great vessels, and Dmean of the Non-GTV Lung and ipsilateral Non-GTV Lung with VMAT-SABR were significantly lower than those of HT-SABR. Our study revealed that VMAT-SABR showed a steeper dose falloff and lower dose of the OARs. VMAT-SABR is a potentially optimal modality to improve the therapeutic ratio compared to HT-SABR in patients with UC lung lesions.