Comparison of Fractionated to Single-Dose Total Body Irradiation in Conditioning Canine Littermates for DLA-Identical Marrow Grafts

We explored the ability of fractionated total body irradia-tion (TBI) given at a rate of 7 cGy/min from opposing dual ‘#{176}Cosources at otherwise lethal doses of 450, 600. 700. 800. and 920 cGy to condition dogs for marrow grafts from DLA-identical littermates. Results were compared with those of a previously reported study using single-dose TBI administered under otherwise identical conditions. Frac-tionated TBI was less immunosuppressive than single-dose TBI. as evidenced by a significantly higher rate of graft rejection (P =.001). Specifically, sustained allogeneic engraftment was observed in only two of 1 8 (1 1 %) dogs that received 600 to 800 cGy fractionated TBI as compared with 1 1 of 1 7 (65%) dogs that received comparable doses of single-dose TBI. Only at 450 cGy (none of the ten dogs studied had sustained engraftment) and at 920 cGy (four o