Risk Factors Of Radiation Pneumonitis In Lung Cancer Patients With Subclinical Interstitial Pulmonary Disease After Thoracic Radiotherapy: A Prospective Observational Study

Previous studies reported that patients with subclinical interstitial pulmonary disease (ILD) were more susceptible to developing radiation pneumonitis (RP) after thoracic stereotactic body radiotherapy or thoracic radiation therapy (TRT). The present study aimed to evaluate the incidence and risk factors of RP after TRT in lung cancer patients with subclinical ILD. A total of 87 consecutive patients with patients with subclinical ILD between January 2016 and December 2017, who were treated with thoracic intensity-modulated radiation therapy at our institution, were analyzed. The diagnosis of subclinical ILD was reviewed by two experienced thoracic radiologists based on the pretreatment high-resolution computed tomography imaging, such as honeycombing, subpleural reticular opacities, ground-glass opacity, and traction bronchiectasis. Statistical analysis was performed using statistical analysis software Univariate and multivariate analyses were used to assess the correlation of clinical factors, preexisting subclinical ILD, and dose-volume histogram-based dosimetric parameters with RP. A P value < 0.05 was considered statistically significant. The median follow-up time was 14.1 months. RP was observed in 19 (21.8%), 27 (31.0%), 10 (11.5%), 3 (3.4%), and 5 (5.7%) patients with grades 1, 2, 3, 4 and 5 RP, respectively. The location of tumors and mean lung dose were associated with an increased risk of ≥grade 2 RP (P=0.043,P=0.024, respectively). Patients who received gemcitabine in the past and the volume of subclinical ILD ≥25% of the lung field were associated with an increased risk of ≥grade 3 RP (P=0.035,P=0.005,respectively). Patients who received gemcitabine in the past and the volume of subclinical ILD ≥25% of the lung field were significantly associated with ≥grade 3 RP in multivariate analysis (P=0.028). Subclinical ILD is associated with an increased risk of RP. Patients who received gemcitabine in the past and the volume of subclinical ILD ≥25% of the lung field were associated with an increased risk of ≥grade 3 RP.