Modifying factors in the influence of irradiation on healing processes in the rat femur: Quality of rays, length of time between surgery and irradiation, recovery from sublethal radiation injuries

The study described was carried out to assess the influence of irradiation on the healing of surgical traumata of the femur inflicted on rats. The results of single-session radiotherapy (using 320 kV X-rays) carried out at different points of time between six hours and 14 days after traumatization led to the conclusion that after six hours radioresistance increases as compared to that seen in preoperative one-staged irradiation. The dose-effect curves for the 24-hour findings did not significantly deviate from relevant observations made before surgery. When more time elapsed after traumatization, the inhibition of bone healing by the effects of irradiation was much less pronounced so that even doses above 35Gy, administered following periods of 7 or 14 days, failed to prevent healing. In order to gain insights into the repair kinetics in sublethal radiation damage further investigations were carried out, in which the radiation dose was divided into four fractions. The determinations were made on the basis of a tentative half-life of one hour, presupposing an exponential reduction of sublethal damage and complete reversibility of any injuries from radiation. (KST)