Development of radiation pneumonitis. Time and dose factors.

Abstract

Histologic evaluation of the lungs was done at autopsy in 215 patients who had received thoracic radiation. The presence or absence of tissue changes noted were: edema, congestion, atelectasis, fibrin exudate in alveoli, epithelial changes, fibrillar thickening of alveolar septa, increased cellularity of alveolar septa, fibrosis of alveolar septa, and proliferative changes in blood vessels. Some or all of the tissue changes listed were found in 165 cases. Two changes were particularly frequent: accumulation of a fibrin-rich exudate within alveoli, often forming a membrane in the lation of fibrillar material, by cellular proliferation, or by increase of fibrous tissue. Such fibrin accumulations were found at radiation doses below 500 r and in excess of 6000 r, and at postirradiation intervals of less than 30 days and over 5 yr. Fibrin accumulations formed within 90 days after less than 1500-r x-ray exposure were similar to those seen almost 9 yr after 5000 r. Three separate types of proliferative changes in the connective tissue of the alveolar septa appeared to be secondary to radiation; 27% showed a fibrillar deposit in the septa which tended to thicken the septa markedly. The time interval appeared to make little difference in the development of thismore » lesion. Increased septal cellularity, due primarily to accumulation of histiocytes and fibroblasts, was seen in 18% of the cases, most commonly at doses between 2000 r and 5000 r. Fibrosis of alveolar septa was the third type of proliferative change and was seen in 42% of the cases. (P.C.H.)« less