Surfactant release as an early measure of radiation pneumonitis.

The immediate release of surfactant into lung alveoli following irradiation has been studied as a potential indicator for the later development of radiation pneumonitis. Utilizing single dose radiation exposure to the whole thorax in male LAF1/J mice, steep dose response curves for lavaged alveolar surfactant were identified at 7 and 28 days after exposure. Seven days after irradiation there was no elevation with doses up to and including 12 Gy; above this dose a detectable increase occurred. At 28 days the surfactant recovered by lavage was elevated compared to the levels seen at day 7 for all doses; doses greater than 12 Gy produced surfactant values significantly greater than those found in mice treated with 12 Gy or less. The radiation pulmonary lethality dose response curve assessed four months later indicated an LD50 value of approximately 13 Gy. The early biochemical effect and the later radiation pneumonitis lethalities therefore closely coincided. The evidence strongly indicates that alveolar surfactant release uncovered hours to days after radiation exposure may be an early biochemical marker that predicts for subsequent pneumonitis radiation injury.