Cell survival kinetics in peripheral blood and bone marrow during total body irradiation for marrow transplantation

Cell survival kinetics in both peripheral blood and in bone marrow have been studied over the time course of hyperfractionated total body irradiation (TBI) for bone marrow transplantation. Our unique TBI regimen allows the study of the in vivo radiation effect uncomplicated by prior cyclophosphamide, since this agent is given after TBI in our cytoreduction scheme. Peripheral blood cell concentrations were monitored with conventional laboratory cell counts and differentials. Absolute bone marrow cell concentrations were monitored by measuring cell concentrations in an aspirate sample and correcting for dilution with blood by a cell cycle kinetic method using cytofluorometry. In the entire group of patients, time to engraftment with donor marrow was found to be 16.6 × 4.4 days and more rapid when a nucleated donor cell dose of ≥4.0 × 10⁸ cells/kg was given. For lymphocytes in peripheral blood in patients in remission, the effective D₀ ranged from 373 rad in 10 children ≤10 y old, to 536 rad in the four patients between 11-17 y old, while n = 1.0 in all groups. There was no trend observed according to age. Granulocytes had a much higher effective D₀, approximately 1000 rad in vivo. Absolute nucleated cell concentration in marrow dropped slowly initially, due to an increased lymphocyte concentration in marrow during a concurrent drop in lymphocyte concentration in peripheral blood, but eventually fell on the last day of TBI ranging from 7-44 % of the initial marrow nucleated cell concentration. Marrow myeloid elements, however, dropped continuously throughout the course of TBI.