BIOLOGICAL EFFECTS OF INHALED (CECL3)-CE-144 IN BEAGLE DOGS

The biological effects of Ce-144 were studied in beagle dogs that were exposed to graded activity levels of (CeCl3)-Ce-144, via a single, br ief inhalation exposure and observed for their life span. The long-ter m 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 Ce- 144 was translocated to liver and skeleton, where the Ce-144 was retai ned with a half-time approaching the physical half-life of Ce-144, 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 i nduced by the beta-particle radiation were noted in the lung, liver, s keleton, bone marrow, and oral and nasal mucosae closely associated wi th bone. Early deaths (within 2.5 years) were generally related to hem atological dyscrasia, radiation pneumonitis, or hepatocellular degener ation and atrophy. Neoplasms that occurred relatively early, from 2.2- 6.8 years after exposure, were noted in the liver, bone, bone marrow a nd oral mucosa closely associated with bone. Neoplasms that occurred l ater, beyond 7 years after exposure, were noted in the liver, lung and nasal mucosa closely associated with bone. Increased numbers of neopl asms were not found in two other organs that had relatively high radia tion doses, namely the thyroid and kidney. Only one primary bone tumor was noted, but 11 tumors of bone-associated tissues (oral and nasal m ucosae and bone marrow) were found. Radiation doses and effects in tis sues adjacent to bone, especially those of epithelial or marrow origin , should be considered when determining risks from internally deposite d bone-seeking radionuclides, such as Ce-144. The property of Ce-144 i n depositing on and remaining associated with bone surfaces for long t imes may be an important factor in the radiation dose to bone marrow a nd epithelium adjacent to bone. (C) 1997 by Radiation Research Society