Lung density changes observed in vivo in rat lungs after irradiation: variations among and within individual lungs.

Lung density measurements using Computed Tomography have been used before at various intervals after irradiation to monitor radiation-induced changes in the lung. The average lung density, its standard deviation which was used as a measure of the density homogeneity throughout the lung, and the densities of smaller lung regions were measured before and up to 76 weeks after irradiation in rat lungs. Large differences in individual response to irradiation were observed. Both increases and decreases in lung density were measured. Regions of very low density were often found adjacent to dense foci of radiation damage. These compensatory changes made the measurement of changes in average lung density an insensitive index of radiation damage. However, the measurement of regional densities in smaller lung volumes, a method not previously applied to rodents, was a much more sensitive index of radiation damage. Changes from non-irradiated control lung densities were observed at earlier times and for lower radiation doses.