Recovery from Radiation Injury in the Hamster as Evaluated by the Split-Dose Technique

The split-dose technique was used to determine the pattern of recovery from radiation injury in the Syrian hamster. Exposure of the animals to 1-mVp X-rays resulted in a${\rm LD}_{50(30)}$of 941 R. Recovery during the first 20 days was found to be nonexponential; in fact, a marked transient increase in radiosensitivity was observed during the second week after a conditioning exposure to 2/3${\rm LD}_{50(30)}$. The patterns of changes in erythrocytes, granulocytes, thrombocytes, and mononuclear cells are discussed in light of the change in the time-dependent radiosensitivity. Survival time was found to be inversely related to exposure-the higher the exposure, the shorter the survival time-in all irradiated groups except the group challenged at 3 days. The survival time at the${\rm LD}_{50(30)}$varied with the day of challenge.