The purpose of this study was to evaluate the impact of emphysematous changes in lung on dosimetric parameters in stereotactic body
radiation therapy (SBRT) for lung
tumor. A total of 72 treatment plans were reviewed, and dosimetric factors [including homogeneity index (HI) and conformity index (CI)] were evaluated. Emphysematous changes in lung were observed in 43 patients (60%). Patients were divided into three groups according to the severity of
emphysema: no
emphysema (n = 29), mild
emphysema (n = 22) and moderate to severe
emphysema groups (n = 21). The HI (P < 0.001) and the CI (P = 0.029) were significantly different in accordance with the severity of
emphysema in one-way analysis of variance (ANOVA). The HI value was significantly higher in the moderate to severe
emphysema group compared with in the no
emphysema (Tukey, P < 0.001) and mild
emphysema groups (P = 0.002). The CI value was significantly higher in the moderate to severe
emphysema group compared with in the no
emphysema group (P = 0.044). In multiple linear regression analysis, the severity of
emphysema (P < 0.001) and the mean material density of the lung within the PTV (P < 0.001) were significant factors for HI, and the mean density of the lung within the PTV (P = 0.005) was the only significant factor for CI. The mean density of the lung within the PTV was significantly different in accordance with the severity of
emphysema (one-way ANOVA, P = 0.008) and the severity of
emphysema (P < 0.001) was one of the significant factors for the density of the lung within the PTV in multiple linear regression analysis. Our results suggest that emphysematous changes in the lung significantly impact on several dosimetric parameters in SBRT, and they should be carefully evaluated before treatment planning.