Early changes in pulmonary function after stereotactic body radiotherapy for lung oligometastases.

[OBJECTIVE] This study aimed to evaluate early pulmonary function changes after stereotactic body radiotherapy (SBRT) in patients with lung oligometastases and to identify predictors of clinically meaningful decline.

[METHODS] This retrospective analysis included 55 patients with 71 lung metastases treated with SBRT between January 2021 and October 2024. Pulmonary function tests (PFTs) were performed before and three months after treatment. Parameters included forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC ratio, vital capacity (VC), and diffusing capacity of the lungs for carbon monoxide (DLCO). A decline of ≥10% from baseline was considered clinically meaningful. Cut-off values were determined by receiver operating characteristic (ROC) analysis. Associations were evaluated using Chi-square tests. Overall survival (OS) was analyzed with the Kaplan-Meier method.

[RESULTS] Mean FEV1 declined from 82.5 ± 22.8% to 78.3 ± 21.2% (P = 0.007), and the FEV1/FVC (% of predicted ratio) decreased from 110.3 ± 14.1% to 106.8 ± 16.2% (P = 0.04). No significant change was observed in FVC, VC, or DLCO. A ≥10% decline in FEV1 was observed in 23.6% of patients (n = 13), and in the FEV1/FVC ratio in 18.1% (n = 10). Clinically meaningful declines were significantly associated with non-small cell lung cancer (NSCLC) histology (P = 0.003), leukocyte count ≥7.18 ×10≥/μL (P = 0.01), metastasis diameter ≥12.5 mm (P = 0.01), and age ≥65 years (P = 0.01). PFT change was not associated with OS.

[CONCLUSION] SBRT in patients with lung oligometastases results in modest early declines in airflow parameters, while lung volumes and gas exchange remain stable. NSCLC histology, systemic inflammation, metastasis size, and age may help identify patients at higher risk.