Acute and late effects of 16- and 50-MeVd leads to Be neutrons on the oral mucosa of rhesus monkeys.

Twenty-five rhesus monkeys were randomly assigned to one of five treatment schedules: 1. control group, no irradiation, 2. 60Co five times weekly, 3. 60Co twice weekly, 4. 16-MeVd leads to Be neutrons twice weekly, and 5. 50-MeVd leads to Be neutrons twice weekly. Although the acute reactions were similar in the four irradiated groups, the late sequelae were more severe in the animals irradiated twice weekly with 60Co or neutrons. All of the animals irradiated with 60Co twice weekly or with 16 MeVd leads to Be neutrons exhibited oromucosal necrosis, whereas none of those irradiated five times weekly with 60Co did. The difference in the effect of photon fractionation on early and late radiation sequelae may be related to different patterns of redistribution of surviving cells through the division cycle in tissues responsible for early and late damage.