The Kinetics of Repair of Sublethal Radiation-Induced Damage in Pig Skin: Studies with Multiple Interfraction Intervals

The kinetics of the repair of radiation-induced sublethal damage (SLD) was studied for the epidermis of the pig. A total of either 7 or 14 interfraction intervals with incomplete repair was achieved by giving 28 fractions either as 7 × 2 fractions/day plus a top-up dose of 17 Gy (half tolerance) or as 14 × 2 fractions/day. The dose per fraction ranged from 1.96-4.82 Gy. A total of 9 intervals ranging from 0.17 h up to 8 h between fractions was used. The incidence of moist desquamation, as an estimate of acute epidermal response, was used as an end point to establish dose-effect relationships. The data were analyzed using either the incomplete repair model of Thames, assuming monoexponential repair kinetics, or a modified version of the incomplete repair model, assuming bi-exponential repair of sublethal damage. Both methods of analysis allowed for the longer overnight interval between fractions. Analysis assuming monoexponential repair gave a T1/2 of 0.74 h for the combined data, although there was a tren...