A mouse embryo-derived cell line, C3H/10T$1\over2$, was used to measure the frequency of in vitro neoplastic transformation induced by 50-kVp X-rays and by fission-spectrum neutrons from the JANUS reactor at the Argonne National Laboratory. The transformation frequency after single X-ray doses rises exponentially, reaching a plateau at about 3 × 10-3 transformant/survivor. The induction curve following single neutron doses, while qualitatively similar, initially rises more steeply and levels off at a maximum of about 6 × 10-3 transformant/survivor. For both radiations, transformation frequency varies with changes in the number of viable cells per dish, showing about a 10-fold decrease in transformation frequency when the number of viable cells per 90-mm dish was increased from about 300 to about 1000. Fractionation of a total X-ray dose of 700 rads results in an approximately 6-fold increase in survival and reduction in transformation frequency over a 16-hr interval. Fractionation of the total neutron dose of 378 rads has no effect upon cell survival, and transformation frequency declines by a factor of only about 1.7 at most over a 24-hr period. Cells derived from transformed foci formed fibrosarcomas when injected into appropriately treated mice.


This research was supported by the United States Department of Energy.

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