Skin Reactions in Mice after Multifraction X-irradiation

Summary

Fractionated doses of 240 kV X-rays were given to one hind leg of mice, and skin reactions were recorded up to 5 weeks after the last dose. The following schedules of irradiation were used: 15 equal fractions in 18 days (15F/18d), 9F/18d, 9F/10d, 5F/9d, 5F/4d, 3F/4d, 2F/2d and single doses. The dose required to produce a given average skin reaction over the period 10 to 32 days, or a corresponding period after multifraction doses, increased steadily with time and fraction number; except for the 9F/10d schedule which produced reactions significantly less than would be expected from any simple sequence. The results are discussed in comparison with other experiments on skin. After allowing for concurrent proliferation, a dose–response curve was derived which had a D_q of 550 rads and a straight portion for doses above 1200 rads. The ratio of initial to final slopes was approximately 0·4 and this indicated the ratio of irreparable to reparable X-ray injury in the skin.