Biological effects of inhaled 144CeCl3 in beagle dogs.

The biological effects of 144Ce were studied in beagle dogs that were exposed to graded activity levels of 144CeCl3 via a single, brief inhalation exposure and observed for their life span. The long-term retained body burdens ranged from 0.06 to 13 MBq/kg with a median of 1.2 MBq/kg. After a short residence time in the lung, most of the 144Ce was translocated to liver and skeleton, where the 144Ce was retained with a half-time approaching the physical half-life of 144Ce, 284 days. Significant radiation doses were delivered to the lung, 28 Gy (median) and 2.5-370 Gy (range); liver, 68 Gy (median) and 6.1-250 Gy (range); and skeleton, 21 Gy (median) and 1.9-100 Gy (range). Lesions induced by the beta-particle radiation were noted in the lung, liver, skeleton, bone marrow, and oral and nasal mucosae closely associated with bone. Early deaths (within 2.5 years) were generally related to hematological dyscrasia, radiation pneumonitis, or hepatocellular degeneration and atrophy. Neoplasms that occurred relatively early, from 2.2-6.8 years after exposure, were noted in the liver, bone, bone marrow and oral mucosa closely associated with bone. Neoplasms that occurred later, beyond 7 years after exposure, were noted in the liver, lung and nasal mucosa closely associated with bone. Increased numbers of neoplasms were not found in two other organs that had relatively high radiation doses, namely the thyroid and kidney. Only one primary bone tumor was noted, but 11 tumors of bone-associated tissues (oral and nasal mucosae and bone marrow) were found. Radiation doses and effects in tissues adjacent to bone, especially those of epithelial or marrow origin, should be considered when determining risks from internally deposited bone-seeking radionuclides, such as 144Ce. The property of 144Ce in depositing on and remaining associated with bone surfaces for long times may be an important factor in the radiation dose to bone marrow and epithelium adjacent to bone.