Aims The use of CTV margins in lung SBRT is not a standard practice due to historically high local control (LC) rates and concerns about toxicity. However, limited data exist evaluating their necessity. This study aims to assess LC outcomes in lung SBRT and investigates the relationship between LC and dose coverage for a hypothetical CTV (hCTV).Methods A retrospective analysis was performed on 126 patients with 140 pulmonary lesions, including histopathologically confirmed (46 %) and clinically diagnosed (54 %) lung cancers. Patients treated with a prescribed BED < 100 Gy to the PTV were excluded. hCTVs were defined using 6 mm margins for squamous cell carcinoma and 8 mm margins for adenocarcinoma or clinically diagnosed lesions, which were further expanded into hypothetical planning target volumes. A ring structure (rCTV) was created by subtracting the GTV from the hCTV. Dose-volume histogram parameters were analyzed, and multivariable analysis assessed their relationship with LC.Results SBRT was delivered with a median BEDα/β: 10 Gy of 124 Gy prescribed to the PTV (range: 100 Gy-151 Gy). The 3-year LC rates were 83.3 %, 80.5 %, 66.9 %, and 71.0 % for lesions measuring ≤10 mm, 11-20 mm, 21-30 mm, and ≥31 mm, respectively. A significant association was identified between the percentage of rCTV receiving BED ≥100 Gy and LC (HR 0.98; P = 0.044).Conclusions Omitting CTV margins in lung-SBRT may compromise LC when rCTV coverage with BED ≥100 Gy is insufficient, warranting further investigation into the clinical benefit of adding CTV margins.
