Risk factors for radiation pneumonitis in lung cancer patients with subclinical interstitial lung disease after thoracic radiation therapy

Background Previous studies have found that patients with subclinical interstitial lung disease (ILD) are highly susceptible to developing radiation pneumonitis (RP) after thoracic radiation therapy. In the present study we aimed to evaluate the incidence of and risk factors for RP after thoracic intensity-modulated radiation therapy in lung cancer patients with subclinical ILD. Methods We retrospectively analyzed data from lung cancer patients with subclinical ILD who were treated with thoracic intensity-modulated radiation therapy with a prescribed dose of ≥ 50 Gy in our institution between January 2016 and December 2017. Results Eighty-seven consecutive lung cancer patients with subclinical ILD were selected for the study. The median follow-up period was 14.0 months. The cumulative incidence of grades ≥ 2 and ≥ 3 RP at one year was 51.0% and 20.9%, respectively. In the multivariate analysis, a mean lung dose ≥ 12 Gy was a significant risk factor for grade ≥ 2 RP (p = 0.049). Chemotherapy with gemcitabine in the past, V5 ≥ 50%, and subclinical ILD involving ≥ 25% of the lung volume were significantly associated with grade ≥ 3 RP (p = 0.046, p = 0.040, and p = 0.024, respectively). Conclusion Mean lung dose is a significant risk factor for grade ≥ 2 RP. Lung cancer patients who have received chemotherapy with gemcitabine in the past, V5 ≥ 50%, and those with subclinical ILD involving ≥ 25% of lung volume have an increased risk of grade ≥ 3 RP in lung cancer patients with subclinical ILD.