Sensitivity to radiation and recovery of hematopoietic stem cells

A function is proposed to approximate the fraction of active hematopoietic stem cells that remain after a time following irradiation by X rays. The parameters in the function are determined by minimizing the root mean square (rms) deviations of the logarithms of the function from the logarithms of the experimentally measured stem cell fractions for mice. The rms deviation obtained is 10%. The zero time limit of the function depends exponentially on the dose decaying with a D0 of 0.43 Gy in contrast to the value 0.9 Gy often quoted. This value 0.43 is shown to be consistent with an LD50 of 5.86 Gy, an average of the values previously reported by Bateman et al. [Radiology 79, 1008-1014 (1962)]. No displacement of the exponential to the right is apparent.