Optimizing the methodology for calculating the 4DCT derived internal target volume in stereotactic radiotherapy for Non-Small Cell Lung Cancer (NSCLC

This study aimed to investigate efficient methods for determining the Internal 
Target Volume (ITV) using Four-Dimensional Computed Tomography (4DCT) 
images in Stereotactic Body Radiotherapy (SBRT) for patients with early-stage 
Non-Small Cell Lung Cancer (NSCLC). The study involved 55 patients who 
underwent SBRT for stage I NSCLC, with their 4D CT images analyzed to 
determine the ITVs. The Matching Index (MI) for ITV4Phases and ITV2Phases 
was calculated as the ratio of these volumes to ITV10Phases. Significant 
differences were observed among the various ITVs, with distinct orders for 
ITV10Phases, ITV4Phases, and ITV2Phases. Notably, the MI for ITV4Phases 
was significantly higher than that for ITV2Phases. Additionally, there was an 
inverse relationship between the MI of ITV4Phases and the Total Motion Index 
(TMI) (r=0.0067, p=0.5507). In a subgroup with low TMI, ITV4Phases did not 
show a significant difference from ITV10Phases (p=0.8003), and its MI was 
significantly higher than that of ITV2Phases.Therefore, ITV4Phases emerges 
as a potentially efficient alternative to the optimal ITV10Phases in SBRT for 
early-stage NSCLC, especially in cases with reduced tumor motion.