LUNG TUMORIGENESIS IN THE SYRIAN-HAMSTER FROM PARTICULATE SOURCES OF PM-147 BETA-RADIATION

Syrian hamsters were exposed to 147Pm β radiation from ceramic microspheres permanently lodged in the capillary bed of the lung. Lung burdens ranged from 6000 to 152,000 spheres, with activities of either 70 or 450 pCi/sphere. Lung burdens of 0.4 to 16 μCi gave initial dose rates of 0.65 to 20.5 krad/year. No life shortening resulted. Tumor incidence increased with the logarithm of dose rate, reaching 30% at about 15 krad/year. Tumor induction time was about 300 days, and the incidence rate reached a maximum at about 600 days postexposure. For all experiments, the distribution of tumor types was 35% adenomas, 41% adenocarcinomas, and 24% epidermoid carcinomas. No other lesions correlated with tumor incidence; in particular, the bronchiolar adenomatoid lesion was not a reliable estimator of tumorigenicity.