AN ULTRASTRUCTURAL STUDY OF THE DEVELOPMENT OF RADIATION INJURY IN THE LUNG
NAVAL RADIOLOGICAL DEFENSE LAB SAN FRANCISCO CA
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Radiation doses of 2000 R were given to the left hemithorax of a group of 25 rats. At intervals of from one hour to one year following irradiation sections of the lung were examined with the electron microscope. The initial site of radiation damage appears to lie chiefly in the endothelium. The endothelium is sloughed and the original endothelial space is replaced by collagen and mast cell infiltrates. Some capillaries are recanalized by new endothelial cells. Eventually these capillaries attain an appearance similar to that of the original capillary but with a slightly thickened endothelium and basement membrane. If the original capillary architecture is not maintained, massive fibrosis results. The mast cell participates extensively in the repair of the radiation damage and is closely associated with collagen and new capillary formation. It is stressed that the degree of damage occurring after a given dose of irradiation varies widely and that these observations were made on only small samples of lungs.