Predictive Factors for Radiation Pneumonitis in Patients Receiving Intensity-modulated Radiation Therapy for Thoracic Malignancy

Abstract

Purpose: It is unknown whether established dose-volume parameters predictive of radiation pneumonitis (RP) are applicable to multiple disease sites. We investigated the factors associated with RP in a heterogeneous population of patients receiving thoracic radiation. Methods and materials: Ninety-nine patients who received thoracic radiation with helical tomotherapy were included in this retrospective chart review. Correlation studies were performed and significant clinical and dosimetric factors predictive for grade ≥ 3 RP were assessed using Cox multivariate analysis (MVA). Results: Fifty-two patients developed RP (grade 1-5), the majority having grade 1 toxicity. Five patients experienced grade ≥ 3 RP. Eleven patients developed ≥ 2 RP. The mean time to RP was 3 months. The sole predictor of RP on MVA was a lung volume receiving a maximum of 20 Gy (VS20) < 1600 cc’s (hazard ratio=14.7, p<0.01). The percentage of lung receiving ≥ 5 Gy or ≥ 20 Gy were not significant predictors for RP. The grade ≥ 3 RP-free survival at 1 year in patients with a VS20 <1600 cc’s versus ≥ 1600 cc’s was 50.0% and 97.1%, respectively (logrank, p<0.01). Results were similar when the RP threshold was lowered to include grade ≥ 2. Conclusions: A VS20 <1600 cc’s is a significant adverse factor associated with RP; this included cases that were RP grade ≥ 3 and ≥ 2. This is a new dosimetric parameter that can be utilized for treatment planning.