Comparison of Lung Carcinoma Incidence in Beagle Dogs Exposed to 239PuO2 as Young Adults or as Immature Dogs

Abstract

Beagle dogs were exposed by inhalation either as immature ("3 months of age) or as young adult (" 13 months of age) dogs to monodisperse particles of 239PuO2. These particles are relatively insoluble in vivo and thus the majority of the radiation dose is delivered to the lung and associated tissues. As have been reported previously there were no apparent differences in lung retention associated with age at exposure. Time-dependent radiation doses to the lung, averaged over the total lung mass, were calculated to take into account the growing lung of the immature dog. There were 108 immature dogs exposed to a monodisperse 1.5 µm AMAD particles (74 survivors are 7-10 years after exposure) and 252 young adults dogs exposed to 0.75, 1.5 or 3.0 µm AMAD particles (52 survivors are 11-13 years after exposure). To date, 24 immature dogs have died with lung carcinomas at doses of 2.5 to 83 Gy and 104 young adult dogs have died with lung carcinomas at doses of 3.2 to 89 Gy. The lung carcinoma incidence rates for the two study groups were compared using a Cox proportional hazards model with a time-dependent dose. A common baseline incidence rate was used so that risks would be estimated relative to the same baseline. No statistically significant difference (P>0.30) was found between the immature and the young adult dogs in how their lung carcinoma incidence rates increased with radiation dose. This suggests that there is not a unique radiosensitivity attributable to alpha particle irradiation of a growing lung.