Pathologic observation of irradiation-induced pulmonary fibrosis in rats with a single dose irradiation to right hemithorax

Objective To observe the pathologic features and regularity of the irradiation-induced rat pulmonary fibrosis. Methods Thirty-five adult male Sprague Dawley rats were divided into 7 groups randomly. In every group 3 rats were irradiated with a single dose of 20 Gy to their right hemithoraxes with an 8 MV linear accelerator and 2 rats were received sham irradiation. On day 1, 3, 7, 14, 28, 84,or 164 after radiation, all animals were sacrificed and the total lungs were harvested for macrography and all middle lobes of the right lungs were resected as the specimens for light and electronic microscope examination. Results Pulmonary parenchyma cells in the irradiated rats showed damaging changes as compared with sham rats on day 1, 3, and 7 after-radiation, and the endothelial injury was ahead of other parenchyma cells. On day 14 and 28 after-irradiation, the major pathological changes of the irradiated lungs consisted of thickening and edema of the alveolar septum as well as the hyperplasia of collagen and fibroblasts. Typical fibrosis focus, renascent endothelium cells and more type Ⅱ pneumocyte, and a large number of phagocytes in alveolar lumen were seen in irradiated lung specimens on day 84 and 168 after-irradiation. Conclusion Endothelial cells may have the most sensitivity to irradiation in all of pulmonary parenchyma cells.