Analysis of the steepness of the dose-incidence curve for necrosis in mouse tails after a multifraction x-ray schedule.

The steepness of the dose-incidence curve for necrosis of mouse tails was measured in detail after a multifractionated schedule of 15 fractions over 19 days. The steepness is compared with curves reported previously for some other rodent and human tissues, and it is analyzed in terms of a composite mean lethal dose for the fractionated treatment of the target cells envisaged as responsible for tail necrosis. It is shown that this dose of 2.3 +/- 0.3 Gy (230 +/- 30 rad) is equivalent to the inverse slope of the tangent to the survival curve for single doses, at the mean dose fraction used of 4.3 Gy (430 rad).