Inactivation of Haemopoietic Stem Cells by Slow α-particles

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Abstract
Inactivation of murine haemopoietic stem cells, assayed as spleen colony-forming units (CFU-S), has been determined after in vitro irradiation under well defined conditions with small numbers (0·15–3) of α-particles of incident energy 3·3 MeV (LET 121 keV μm−1). Exponential survival curves were obtained with inactivation dose coefficients of 1·83±0·11 and 1·63±0·06 Gy−1 for 8 and 12-day CFU-S, respectively, corresponding to inactivation cross sections of 35·6±2·1 and 31·7±1·2 μm2. The results indicate that these radiosensitive stem cells have a significant probability of surviving the passage of a single α-particle track, estimated at 8 and 18% per particle passage, respectively, if the cells have a diameter of 7 μm. However, this estimation is strongly dependent on the assumed diameter. Conversely, it is demonstrated that the cells cannot have mean geometric diameters of less than 6·7±0·2 and 6·4±0·1 μm, respectively. Associated experiments have shown that some cells from the irradiated population do survive to form colonies that express delayed non-clonal chromosome aberrations.
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