MARROW TOXICITY OF FRACTIONATED VS SINGLE-DOSE TOTAL-BODY IRRADIATIONIS IDENTICAL IN A CANINE MODEL

Purpose: We explored in dogs the marrow toxicity of single dose total body irradiation delivered from two opposing Co-60 sources at a rate o f 10 cGy/min and compared results to those seen with total body irradi ation administered in 100 cGy fractions with minimum interfraction int ervals of 6 hr. Dogs were not given marrow transplants. Results: We fo und that 200 cGy single dose total body irradiation was sublethal, wit h 12 of 13 dogs showing hematopoietic recovery and survival. Seven of 21 dogs given 300 cGy single dose total body irradiation survived comp ared to 6 of 10 dogs given 300 cGy fractionated total body irradiation (p = .18). One of 28 dogs given 400 cGy single dose total body irradi ation survived compared to none of six given fractionated radiation (p > .20). With granulocyte colony stimulating factor administered from day 0-21 after 400 cGy total body irradiation, most dogs survived with hematological recovery. Because of the almost uniform success with gr anulocyte colony stimulating factor after 400 cGy single dose total bo dy irradiation, a study of granulocyte colony stimulating factor after 400 cGy fractionated total body irradiation was deemed not to be info rmative and, thus, not carried out. Additional comparisons between sin gle dose and fractionated total body irradiation were carried out with granulocyte colony stimulating factor administered after 500 and 600 cGy of total body irradiation. As with lower doses of total body irrad iation, no significant survival differences were seen between the two modes of total body irradiation, and only 3 of 26 dogs studied survive d with complete hematological recovery. Overall, therefore, survival a mong dogs given single dose total body irradiation was not different f rom that of dogs given fractionated total body irradiation (p = .67). Similarly, the slopes of the postirradiation declines of granulocyte a nd platelet counts and the rates of their recovery in surviving dogs g iven equal total doses of single versus fractionated total body irradi ation were indistinguishable. Conclusion: Within the limitations of th e experimental design, we conclude that single-dose and fractionated t otal body irradiation have comparable marrow toxicity in dogs.