Biological effects of ²²⁴Ra and ²²⁶Ra and their relative radiotoxicity in mice

Summary

Groups of ten-week-old ICR SPF female mice were treated intraperitoneally with 3 levels of ²²⁴Ra and ²²⁶Ra activities. The administration scheme provided the skeletal dose from ²²⁴Ra and its daughter products (T series of mice) comparable to that resulting from a single injection of ²²⁶Ra (U series of mice). Three hundred mice in each experimental series and 400 controls, kept under standard conditions till their death, were evaluated. The mean survival time of mice was found to become shorter in dependent on the increasing quantity of administered radionuclides and in mice with comparable skeletal doses some biological effects of ²²⁴Ra were found to surpass those of ²²⁶Ra. All mice were examined roentgenographically and histopathologically after their death. Osteosarcoma induction was observed more frequently after injections of ²²⁴Ra than after ²²⁶Ra incorporation. Only a single bone tumour was detected in the group of control mice.

The presented experimental findings seem to lead to a general conclusion that, at the same skeletal dose, the relative radiotoxicity of ²²⁴Ra is about 4 times higher than the toxicity of ²²⁶Ra. The possibility of how to compare experimental results obtained in various laboratories is also discussed.