Sublethal damage in cells of the mouse gut after mixed treatment with X rays and fast neutrons.

The effect of combining X ray and neutron irradiations on cell survival in the mouse intestine has been investigated. The irradiations from the two beams were given within minutes or at most a few hours of each other when recovery from sublethal damage was not always complete. The results show that cells surviving the first dose of radiation have accumulated the same amount of recoverable sublethal damage regardless of whether that first dose was with X rays or neutrons. The rate at which the sublethal damage is shed is the same after X rays or neutrons. It is reasoned that there is less sparing of damage by fractionation of neutron dose compared with fractionation of X ray dose not because there is less recovery from sublethal damage after neutrons but because there is relatively more lethal damage; the recovery from any sublethal damage is the same as if it were from X rays. If X rays and neutron doses are separated by times long enough to allow the full repair of sublethal injury then the combined effect is simply additive.