PRACTICAL AND THEORETICAL CONSIDERATIONS IN THE USE OF THE MOUSE FOOT SYSTEM TO DERIVE EPITHELIAL STEM-CELL SURVIVAL PARAMETERS

A series of experiments investigating the effects of 1, 2, 4, 10, and 20 dose fractions of X rays on mouse foot skin are reported. These include data for levels of acute gross reactions from dry to full moist desquamation. We have shown the following for the irradiated epidermal stem cell population of the mouse foot. Detectable proliferation was not found for regimes employing 10 daily dose fractions. Significant interexperimental variation occurred which did not result from changes in cellular radiosensitivity. The cell-survival equation obtained from data limited to reactions below the point of moist desquamation was not different from that obtained from higher reaction data. The absolute target cell-survival levels corresponding to our mean reaction scale were established using published skin clone data and extended down to 4 X 10-8, and the clonogenic population was estimated as 0.6 to 3.0 X 107. The relative radiobiological usefulness of the various levels of acute reactions has been characterized. Skin-reaction scores obtained by averaging reactions over 7 days encompassing the peak response gave the same results with fewer readings than the conventional 22-day averaging period.