BIOLOGICAL DOSIMETRY OF BONE-MARROW FOR INCORPORATED Y-90

The biological response of bone marrow to incorporated radionuclides d epends on several factors such as absorbed dose, dose rate, proliferat ion and marrow reserve, The determination of the dose rate and absorbe d dose to bone marrow from incorporated radionuclides is complex, This research used survival of granulocyte-macrophage colony-forming cells (GM-CFCs) as a biological dosimeter to determine experimentally the d ose rate and dose to bone marrow after administration of Y-90-citrate, Methods: The radiochemical Y-90-citrate was administered intravenousl y to Swiss Webster mice, Biokinetics studies indicated that the inject ed Y-90 quickly localized in the femurs (0.8% ID/femur) and cleared wi th an effective half-time of 62 hr, Subsequently, GM-CFC survival was determined as a function of femur uptake and injected activity, Finall y, to calibrate GM-CFC survival as a biological dosimeter, mice were i rradiated with external Cs-137 gamma rays at dose rates that decreased exponentially with a half-time of 62 hr, Results: Femur uptake was li nearly proportional to injected activity, The survival of GM-CFCs was exponentially dependent on both the initial Y-90 femur activity and th e initial dose rate from external Cs-137 gamma rays with 5.1 kBq/femur and 1.9 cGy/hr, respectively, required to achieve 37% survival. Thus, Y-90-citrate delivers a dose rate of 0.37 cGy/hr to the femoral marro w per kBq of femur activity and the dose rate decreased with an effect ive half-time of 62 hr, Conclusion: Survival of GM-CFCs can serve as a biological dosimeter to experimentally determine the dose rate kineti cs in bone marrow.