INFLUENCE OF DOSE-RATE ON SURVIVAL-TIME FOR 239PUO2-INDUCED RADIATION PNEUMONITIS OR PULMONARY FIBROSIS IN DOGS

Beagle dogs were exposed once or repeatedly to 0.75-μm-diameter monodisperse aerosols of 239PuO2 by pernasal inhalation. The dogs that were exposed once received alveolar depositions (±standard deviation) of 3.9 ± 1.9 kBq/kg body mass and accumulated doses of 23 ± 8 Gy to the lung before death at 5.4 ± 1.7 years after exposure. Dogs exposed repeatedly received a total alveolar deposition of 5.3 ± 0.9 kBq/kg body mass during 7 to 10 semiannual exposures and accumulated doses of 22 ± 5 Gy to the lung before death at 4.9 ± 0.7 years after first exposure. Clearance of the plutonium from the lung in the dogs exposed repeatedly was slower than in the dogs exposed once. All dogs in the repeated-exposure study and all but one dog in the single-exposure study died from radiation effects. Pulmonary fibrosis accounted for 72% of the radiation-related deaths in the single- exposure study and 87% in the repeated-exposure study. The remaining dogs died with pulmonary cancer. Based on total cumulative radiation dose, the times after exposure to death from radiation pneumonitis and pulmonary fibrosis were not significantly different for single and repeated exposures. Thus dose rate does not appear to be an important factor in predicting death from radiation pneumonitis or pulmonary fibrosis for dogs inhaling 239PuO2.