We have developed a rat model of single, sub-lethal thoracic irradiation. Our irradiation protocol is considered representative of exposures near the detonation site of a dirty bomb or small nuclear device. The model is being used to investigate techniques for identifying, triaging and treating possible victims. In addition to physiological markers of right ventricular hypertrophy, pulmonary vascular resistance, and arterial distensibility, we present two methods for quantifying microvascular density. We used methods including microfocal X-ray imaging to investigate changes in lung structure/function resulting from radiation exposure. Radiation pneumonitis is a complication in subjects receiving thoracic irradiation. A radiographic hallmark of acute radiation pneumonitis is a diffuse infiltrate corresponding to the radiation treatment field. We describe two methods for quantifying small artery dropout that occurs in the model at the same time-period. Rats were examined 3-days, 2-weeks, 1-month (m), 2-m, 5-m, and 12-m post-irradiation and compared with aged-matched controls. Right ventricular hypertrophy and increases in pulmonary vascular resistance were present during the pneumonitis phase. Vascular injury was dependent on dose and post-irradiation duration. Rats irradiated with 5 Gy had few detectable changes, whereas 10 Gy resulted in a significant decrease in both microvascular density and arterial distensibility around 2- m, the decrease in each lessening, but extending through 12-m. In conclusion, rats irradiated with a 10 Gy dose had changes in vascular structure concurrent with the onset of radiation pneumonitis that were detectable with our imaging techniques and these structural changes persist after resolution of the pneumonitis
