Relative effectiveness of ²⁴¹Am vs ²²⁶Ra approached by haemopoietic stem cell studies in various bone marrow sites of contaminated mice

Haemopoietic stem cell assays allow investigation of local radiation damage at any time after contamination. These techniques were used to determine the relative effectiveness of ²⁴¹Am and ²²⁶Ra in inducing damage in various cortical and trabecular bone marrow sites. Male Balb/c mice were injected with either 230 or 660 kBq ²²⁶RaCl₂/kg body weight or with one of three doses of monomeric ²⁴¹Am citrate at 138, 552 or 768 kBq ²⁴¹Am/kg body weight. At 7 time intervals after injection (from 4 hr to 100 days) the colony-forming capacity of pluripotent stem cells (=CFU-s) and macrophage-granulocyte committed stem cells (CFU-c) was assayed in sternal marrow, marrow of lumbar vertebrae, of the trabecular distal end of the femur and of the femoral shaft (in which were distinguished axial marrow and marrow situated peripherally near the cortical bone). ²²⁶Ra retention and ²⁴¹Am retention were measured in these bone sites. Skeletal doses and doses to the bone marrow sites were calculated. On the base of injected activity, ²⁴¹Am was more effective than ²²⁶Ra in reducing the number of CFU-s and CFU-c but the effectiveness varied in the various bone marrow sites. CFU-s and CFU-c response is considered in relation to the retained radioactivity in the surrounding bone matrix and in relation to the mean marrow dose.