The Incidence and Risk Factors of Chronic Pulmonary Infection after Radiotherapy in Patients with Lung Cancer

Purpose This study aimed to investigate cumulative incidence and risk factors associated with chronic pulmonary infection (CPI) development after radiotherapy for lung cancer. Materials and Methods We retrospectively analyzed 1,872 patients with lung cancer who received radiotherapy for lung cancer from 2010-2014, had a follow-up period of ≥ 3 months after radiotherapy, and did not have CPI at the time of radiotherapy. CPI was defined as pulmonary tuberculosis, non-tuberculous mycobacterial pulmonary disease, chronic pulmonary aspergillosis, or pulmonary actinomycosis. The cumulative incidence of CPI and overall survival (OS) were estimated using the Kaplan-Meier method, and a multivariable Cox proportional hazards analysis was performed to identify risk factors associated with CPI development. Results The median follow-up period was 2.3 years with OS rates of 55.6% and 37.6% at 2 and 5 years, respectively. CPI developed in 59 patients at a median of 1.8 years after radiotherapy, with cumulative incidence rates of 1.1%, 3.4%, 5.0%, and 6.8% at 1, 3, 5, and 7 years, respectively. A lower body mass index, interstitial lung disease, prior pulmonary tuberculosis, larger clinical target volume, history of lung cancer surgery or radiation pneumonitis, and use of inhaled corticosteroids were independent risk factors for CPI development. Conclusion The long-term survival rate of lung cancer patients receiving radiotherapy was not low, but the cumulative incidence of CPI gradually increased to 6.8% at 7 years after radiotherapy. Therefore, close monitoring of CPI development is required in surviving patients with risk factors.