Repair in Mouse Lung after Split Doses of X Rays

A lung function assay in situ has been used to investigate repair of X-ray injury in mice using two equal doses separated by 1, 7, or 28 days. Dose-response curves were obtained at 2-week intervals up to 28 weeks and at monthly intervals up to 48 weeks. The D₂-D₁ values for early damage (radiation pneumonitis), i.e., 28 weeks after the second dose of radiation, were 3.95 (0-1 day), 4.80 (0-7 days), and 5.50 (0-28 days) Gy. These data agree well with repair values obtained from LD50 data from the same mice. The D₂-D₁ between 1 and 28 days was not as large (1.49 to 1.79 Gy) as that reported previously (3.60 Gy) by S. B. Field, S. Hornsey, and Y. Kutsutani (Br. J. Radiol. 49, 700-707 (1976)), although it demonstrated significant slow repair. A clear dissociation of early pneumonitis and late fibrosis was observed in the mice, occurring only after the lowest total split dose given (19 Gy) and becoming more clearly dissociated as the time between the two doses was increased.