Experimental stereotactic irradiation of normal rabbit lung: computed tomographic analysis of radiation injury and the histopathological features

The aim of this study was to establish an animal experimental model of pulmonary stereotactic irradiation and clarify the morphological patterns of pulmonary radiation injury with computed tomography and the histopathological features. Tiny spherical regions in the lungs of seven anesthetized rabbits were irradiated stereotactically with a single fractional dose of 21-60 Gy. Subsequently, the irradiated lungs were observed biweekly with computed tomography (CT) for 24 weeks. Radiation injury of the lung was examined histopathologically in one specimen. Localized hypodense changes were observed 7-15 weeks after irradiation in three rabbits irradiated with 60 Gy, and the findings persisted beyond that time. The electron density ratios in the lung fields obtained from the CT images were shown to be decreasing, corresponding to the hypodensity changes. No clear increased density opacity was observed in any rabbit in the 60-Gy irradiated group. Severe localized fibrotic change was observed in the histopathological specimens. Specific localized hypodensity changes were found in only three rabbits irradiated with 60 Gy, the highest dose we employed.