Prediction of radiation pneumonitis following high-dose thoracic radiation therapy by 3 gy/fraction for non-small cell lung cancer: Analysis of clinical and dosimetric factors

Objective: This study was undertaken to identify the factors predictive of radiation pneumonitis (RP) in 69 non-small cell lung cancer patients treated with thoracic radiation therapy only by 3 Gy fractions. Methods: A total of 69 patients who received only RT in daily 3 Gy were included in this study. Grade ≥3 RP was defined as an RP event. The cumulative incidence of RP was estimated and the correlations of the development of RP with the potential predictors were determined. Results: The cumulative incidence of events was 17.1% at 12 months. By univariate analysis, all clinical factors [age, performance status, weight loss, pre-RT forced expiratory volume in 1 s, tumour location, stage, RT dose and clinical target volume] were not associated with the risk of Grade ≥3 RP; however, all dosimetric factors [V5-50 and mean lung dose (MLD)] closely correlated with the development of RP. The receiver-operative characteristics (ROC) analysis revealed that MLD was the best predictors of Grade ≥3 RP (area under curve ROC = 0.937). By multivariate analysis, MLD was the only significant factor to be predictive of RP risk: the probability of Grade ≥3 RP was 3.7% when MLD ≤ 16.1 Gy and 78.4% when MLD > 16.1 Gy. Conclusions: Dosimetric parameters were valuable in predicting the development of RP.