Comparative pulmonary carcinogenicity of inhaled beta-emitting radionuclides in beagle dogs.

Beta-emitting radionuclides are important constituents of isotope inventories in light water reactors and may pose an inhalation hazard to industrial workers or the general population if they are released. To study the biological effects of such potential exposures, a series of life span studies was initiated in which beagle dogs were exposed to aerosols of relatively insoluble fused clay particles containing 90Y, 91Y, 144Ce or 90Sr. Groups of dogs exposed to each radionuclide received graded initial lung burdens of radioactivity. When combined with the varied physical half-lives of the four radionuclides, this resulted in a wide variety of radiation doses and dose patterns to the lung. Deaths (greater than 640 days after exposure) were generally associated with pulmonary neoplasia in dogs that inhaled 91Y, 144Ce or 90Sr. These dogs had cumulative lung doses to death greater than 20 000 rads. Exposure to 144Ce or 90Sr with dose rates that decreased slowly induced pulmonary haemangiosarcomas. Pulmonary irradiation from 91Y, with a rapidly decreasing dose rate, resulted in pulmonary epithelial tumours. No malignant lung tumours have been seen within 1540 days after exposure to 90Y. The animals in the main studies have been observed for 1342 to 2756 days after exposure.