Incidence of radiation pneumonitis after thoracic irradiation: Dose-volume correlates

PURPOSE: To define clinical and dosimetric parameters correlated with the risk of clinically relevant radiation pneumonitis (RP) after thoracic radiotherapy. METHODS AND MATERIALS: Records of consecutive patients treated with definitive thoracic radiotherapy were retrospectively reviewed for the incidence of RP of Grade 2 or greater by the Common Toxicity Criteria. Dose-volume histograms using total lung volume (TL) and TL minus gross tumor volume (TL-G) were created with and without heterogeneity corrections. Mean lung dose (MLD), effective lung volume (V(eff)), and percentage of TL or TL-G receiving greater than or equal to 10, 13, 15, 20, and 30 Gy (V10-V30, respectively) were analyzed by logistic regression. Receiver operating characteristic (ROC) curves were generated to estimate RP predictive values. RESULTS: Twelve cases of RP were identified in 92 eligible patients. Mean lung dose, V10, V13, V15, V20, and V(eff) were significantly correlated to RP. Combinations of MLD, V(eff), V20, and V30 lost significance using TL-G and heterogeneity corrections. Receiver operating characteristic analysis determined V10 and V13 as the best predictors of RP risk, with a decrease in predictive value above those volumes. CONCLUSIONS: Intrathoracic radiotherapy should be planned with caution when using radiotherapy techniques delivering doses of 10 to 15 Gy to large lung volumes.