Development of experimental radiation pneumonitis.

Abstract

Histologic changes were studied in the lungs of rats irradiated with 3000 r to the thorax witn shielding of the remainder of the body. In some animals the same total dose was given as 5 weekly doses of 600 r or in 2 doses spaced 50 daya apart. Development of radiation pneumonitis in rats was characterized by an early inflammatory reaction with progressive organization of fibrin-rich edema fluid in alveolar septa. Later stages showed thickened aiveolar septa containing large numbers of heavy reticulum fibers. Fractionation of radiation, either by multiple weekly doses or 2 large doses at a 7-week interval, did not appreclably alter the development of radiation pneumonitis. This suggests that previous exposure does not make the lung more radiosensitive but that the parenchymal changes are a function primarily of the total radiation dosage. Observations in the lung conformed with results in longevity studies showing that there is relatively rapid recovery from radiosensitivity induced by previous exposure. Rats exposed to massive thoracic radiation developed acute necrotizing esophagitis, resulting in extensive mortality. In contrast to the changes in man foliowing thoracic radiation, the development of a hyaline membrane was not conspicuous in rats. Thus it is doubtful that organization ofmore » a hyaiine membrane plays a significant part in the fibrous thickening of alveolar septa in the animals. (H.H.D.)« less