The Response of Pig Skin to Fractionated Treatments with Fast Neutrons and X rays

The skin of pigs has been used to study the effect of fractionated irradiation with fast neutrons of mean energy 6 MeV. Six, nine and 15 fractions have been used over a period of three weeks, and two fractions divided by short intervals of time up to 24 hours. The effects of fractionated treatments with X rays are also summarised. The RBE of the neutron beam rises steadily from 2·3 for a single dose to 3·6 for 15 fractions. Observations up to five years after treatment have failed to show any sign of increased late reactions after neutrons. There is less recovery during a fractionated course of treatment with fast neutrons than with X rays, the relative amount of recovery being 0·6. Very little recovery was observed during the first seven hours after treatment with neutrons. Reactions occurring after fractionated treatments with X rays show that the number of fractions is more important than the time over which the treatment is extended, up to 28 days, but that prolongation is nevertheless a significant factor.