Idiopathic pulmonary fibrosis (IPF) is associated with fatal complications after radiotherapy (RT) for lung cancer patients. This study evaluated 264 patients with stage I-II non-small cell lung cancer (NSCLC) treated with definitive RT alone, and analyzed 30 patients (11.4%) who had underlying IPF. Among these, X-ray and proton RT were delivered to 22 and 8 patients. All living patients were followed-up at least 9 months.

Treatment-related death occurred in four patients (18.2%) treated with X-ray but none with proton therapy. The 1-year overall survival (OS) rate in patients treated with X-ray and proton was 46.4 and 66.7%, respectively, and patients treated with proton therapy showed a tendency of better survival compared to X-ray (p = 0.081). This study concluded that RT is associated with serious treatment-related complications in patients with IPF. Proton therapy may be helpful to reduce these acute and fatal complications.