Repeated Inhalation Exposure of Mice to 144 CeO 2 : II. Biologic Effects

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Abstract
Groups of mice (C57Bl/6J strain) were repeatedly exposed by inhalation to aerosols of 144CeO2 at 60 day intervals for 7 consecutive exposures to reestablish lung burdens of 144Ce of 0.2, 1.0 or 4.5 .mu.Ci. Additional groups of mice were exposed only once when 70 days old to achieve desired initial lung burdens of 0.2, 1.0 or 4.5 .mu.Ci. Control mice consisted of mice exposed once or repeatedly to stable CeO2, sham-exposed once or repeatedly and unexposed mice. Protraction of the absorbed radiation dose by repeated inhalation exposures resulted in a sparing from the life-shortening effects of 144Ce pulmonary irradiation. The protraction of dose had no effect on the total number of lung tumors or their time of onset. The total incidence of lung tumors, benign and malignant, was correlated with cumulative dose, not dose rate. [The pattern of pulmonary radiation dose (accumulation of absorbed radiation dose with time) may also be an important factor in pulmonary carcinogenesis with inhaled .beta.-.gamma.-emitting radionuclides.].

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