Using research in primary care: a workbook for health professionals

Similar effects on murine haemopoietic compartment of low dose rate single dose and high dose rate fractionated total body irradiation. Summary This study was designed to compare two different modalities of TBI which are currently used in clinical practice. The same dose of 750 cGy was given to CBA mice either in a single dose at a low dose rate (4 cGy min-') (STBI) or in a fractionated regimen (six fractions of 125 cGy three times a day) at a higher dose rate (25 cGy min ')(FTBI). After TBI completion we simultaneously studied the in vivo radiation response of bone marrow cells, two murine bone marrow clonogenic cells (CFU-S and GM-CFC) and peripheral blood lymphocytes and granulocytes for a period of 1 month. The percentage of spleen erythrocytic and granulocytic colonies was also determined. No significant differences were observed between the two groups in the first 48 hours after irradiation except in bone marrow cell numbers, probably due to differences in the overall treatment time between the two TBI schedules. After the first 48 hours the repopulation patterns of the different cells were very similar in both groups. These findings suggest that the different dose rates and fractionation used in this study caused similar radiation damage to the murine haemopoietic system. Moreover, no significant repopulation occurred during the longer overall treatment time of the fractionated regimen. These preliminary results must be corroborated with a larger range of doses before any firm conclusion can be drawn. Recently fractionated total body irradiation (FTBI) schedules have been favoured over single dose total body irradiation (STBI) because they are thought to increase the differential effect between lung and haemopietic tissues (Peters, 1980; Peters et al., 1979). Lung cells are capable of repairing radiation damage as opposed to haemopoietic stem cells thought to have no or a very limited capacity for repair (Evans et al.,