2162 - Outcomes of Patients with Interstitial Lung Disease and Early-Stage Non-Small Cell Lung Cancer Treated with Stereotactic Body Radiotherapy

S. Vuong¹, M. Liu¹, E. Wallat², M. F. Bassetti², and A. M. Baschnagel²; ¹University of Wisconsin School of Medicine and Public Health, Madison, WI, ²Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, WI

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) provides excellent tumor control with low toxicity in patients with early-stage non-small cell lung cancer (NSCLC). However, data on the safety of SBRT for patients with pre-existing interstitial lung disease (ILD) is limited. The objective of this research is to identify clinical factors that predict for adverse events in patients with ILD and early-stage NSCLC. Materials/

Methods: Patients with Stage I-II NSCLC receiving curative intent SBRT January 2004 to March 2023 were included. Radiation pneumonitis (RP) was scored retrospectively using CTCAE v5. Pretreatment characteristics, lung dosimetrics, and clinical variables were assessed by univariate analysis. Cox regression, adjusted for the competing risk of death, was used to assess factors predicting for overall survival (OS), grade =2 RP, and pulmonary-related admissions within one year.
Results: Of the 436 patients assessed, 31 had ILD prior to SBRT. Median follow-up time was 26.7 months in patients with ILD and 26.6 months in patients without ILD. Median tumor diameters were 1.80 cm for the ILD group and 1.70 cm for those without ILD (P=0.45). At baseline, median predicted forced expiratory volume in one second was 75% (IQR 65%-83%) for the ILD group and 66% (IQR 46%-81%) for those without ILD (P=0.04). Median predicted diffusion capacity of the lung for carbon monoxide (DLCO) was 47% (IQR 29%-54%) for the ILD group and 58% (IQR 44%-73%) for those without ILD (P=0.001). Grade =2 RP occurred in 23 patients (5%), including 5 (16%) with ILD and 18 (4%) without ILD (P=0.005). Grade =3 RP occurred in 2 (6.5%) patients with ILD and 3 (0.7%) without ILD (P=0.004). Pulmonary-related admissions within one year occurred in 73 patients (17%), including 9 (29%) with ILD and 64 (16%) without ILD (P=0.05). Factors predicting for pulmonary admissions within one year were lower baseline DLCO (P=0.01), lower Eastern Cooperative Oncology Group (ECOG) performance status (P=0.03), baseline oxygen use (P<0.001), and COPD (P=0.03). In the first year after SBRT, there were 3 (9.6%) deaths in the ILD group (2 due to respiratory deterioration) and 32 (7.9%) deaths in those without ILD (11 due to respiratory deterioration) (P=0.63). Lower baseline DLCO (P<0.001), lower ECOG performance status (P<0.001), larger tumor size (P=0.006), and baseline oxygen usage (P=0.002) predicted for worse OS. On competing risk analysis, ILD was predictive for pulmonary-related admissions within one year (HR 2.21; 95% CI 1.01-4.442; P=0.02) and grade =2 RP (HR 4.179; 95% CI 1.551-11.262; P=0.005), but not predictive for OS (HR 1.71; 95% CI 0.923-3.17; P=0.08). The volume of lung receiving 10Gy through 50Gy and mean lung dose did not predict for grade =2 RP in patients with ILD.
Conclusion: ILD is associated with increased risk of pulmonary-related admissions and grade =2 RP within one year of treatment with SBRT in patients with NSCLC. Patients with ILD should be carefully selected for SBRT and closely monitored for adverse outcomes following SBRT.