Early and late normal tissue damage after fast neutrons

Abstract

The relative effects of neutrons and X-rays in causing both early and late damage to normal tissues is discussed. For neutrons produced by 16 MeV deuterons on beryllium the RBE as a function of dose per fraction is given for various tissues, some of which respond soon after treatment and some much later. For skin damage the RBE is the same for 4 different species and the relationship between early and late skin damage is the same for X-rays and neutrons for at least 15 fractions given in 3 weeks. Some aspects of the relationship between the early and late forms of skin damage are discussed. The response of lung and the nervous system, both of which occur many months after irradiation, are considered and lung is shown to have a lower RBE than most other tissues. There may be a slow repair process in slowly dividing tissues, in addition to “Elkind repair” of sublethal damage and cellular re-population. There is evidence that slow repair occurs for X-rays and not for neutrons. One consequence is that the RBE for slowly dividing tissues may be increased by lengthening the overall treatment time, and retreatment after a prior course of neutron therapy may be hazardous.