The toxicity of insoluble cerium-144 inhaled by beagle dogs: non-neoplastic effects

The biological effects of inhaled beta-particle-emitting radionuclides are not well known. The non-neoplastic diseases induced by an inhaled, relatively insoluble form of cerium-144 ((144)Ce) were studied in beagle dogs exposed to graded activity levels of (144)Ce in fused aluminosilicate particles by a single, brief inhalation exposure and observed for their life span. The initial lung burdens (ILBs) achieved ranged from 0.000093-7.6 MBq (144)Ce/kg body weight. The (144)Ce was retained in the lung with an effective half-life of about 190 days. Significant (144)Ce was translocated to the tracheobronchial lymph nodes, and the concentration exceeded that of the lung at about 400 days after inhalation exposure. Significant radiation doses were delivered to the lung and tracheobronchial lymph nodes and to the heart adjacent to the tracheobronchial lymph nodes. Radiation pneumonitis was the predominant non-neoplastic disease. The dose response for radiation pneumonitis indicated that an ILB of 1.4 MBq/kg would cause death from radiation pneumonitis in 50% of the exposed dogs. This ILB resulted in a pulmonary dose to death of about 350 Gy. The tracheobronchial lymph nodes developed lesions in dogs with ILBs lower than those causing radiation pneumonitis. The overall results of this study, however, showed that (144)Ce, inhaled in an insoluble form, did not cause any unique or inexplicable biological effects in dogs or cause effects at unusually low doses that might call current radiation protection guidelines into question.