Re-irradiation of rat tails to necrosis at six months after treatment with a “tolerance” dose of X rays or neutrons

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Abstract
Rat tails were re-irradiated to necrosis levels at about 6 mo. after various fractionated treatments with 290 kV X-rays or 14 MeV neutrons. The X-ray dose required to produce necrosis in half of a group of tails (ND50), which were heavily X-irradiated 6 mo. before, was 91 .+-. 4% of the ND50 for aged controls. After prior neutron-irradiation, this value was 87 .+-. 4% (neutrons in 2nd treatment) or 75 .+-. 5% (X-rays in 2nd course). The effective oxygenation of mouse tails at this time after X-irradiation was similar to that of controls; thus these percentage dose values indicated the remarkable tolerance of this organized tissue to a 2nd course of X-irradiation and the presence of more residual injury in neutron-irradiated tissues.