Efficacy and Safety of Thoracic Radiotherapy in Locally Advanced Non-Small Cell Lung Cancer Patients With Pre-Existing Interstitial Lung Diseases: A Single Center Experience of 85 Cases.

Purpose/Objective(s) Whether thoracic radiotherapy (TRT) could be applied to interstitial lung diseases and lung cancer (ILD-LC) patients safely remains unclear. This retrospective study aims to evaluate the efficacy and safety of definitive TRT in locally advanced non-small cell lung cancer (LA-NSCLC) patients with pre-existing ILD, and to analyze the associated risk factors for radiation induced lung toxicities (RILTs) in the clinical setting. Materials/Methods Patients with histologically confirmed LA-NSCLC and pre-existing ILD treated definitive TRT between 2010 and 2019 were retrospectively reviewed. Patient, tumor, and treatment characteristics were evaluated to determine the risk factors for RILTs. Pre-radiation CT of all patients were reviewed by two radiologists and one pulmonologist and are scored according to Muller's thin-section CT scoring system for IPF: 0-no discrete honeycombing, with interlobular septal thickening; 1-honeycombing involving 0-5% of the lobe; 2-honeycombing 6-24%; 3-honeycombing 25-49%; 4-honeycombing 50-74%;5-honeycombing > 75%. Univariate and multivariate analyses with logistic regression models and cox proportional hazards approach were performed to identify the risk factor(s) of RILTs and overall survival (OS) respectively. Results Among 1261 LA-NSCLC patients, 85 were found with pre-existing ILD and enrolled in the analysis. 36.5% of them were scored more than 1 point on CT. 20% patients developed G3+ RILTs within 1 year after the last irradiation, with remarkably 11.8% dying from lung toxicities. And the incidence of symptomatic (G3+) RILTs abruptly dropped to 11.1% (6/54), 3.8% (1/26), and 0% (0/19) for patients with CT score ≤1, V20 1 and V20 ≥ 20% were independently associated with higher risk of G3+ RILTs. The median OS and PFS were 14.0 months and 7.4 month respectively. In the univariate analysis for OS, clinical stage and G3+RILT were evaluated as risk factors while patients in low-risk group, defined as honeycombing score Conclusion Honeycombing score > 1 and V20 ≥ 20% were significantly associated with high incidence of severe lung toxicities, leading to poor survival. However, patients at low risk might benefit from TRT with a considerable overall survival.