Quantitative determination of tolerance doses for preoperative and postoperative radiotherapy of bones

A method has been developed for the quantitative determination of the tolerance doses for preoperative and postoperative radiotherapy of bones in New Zealand white rabbits. The midshaft osteotomy was carried out on both ulnae of each rabbit. Localized radiation of 2000, 3000, and 4000 rad (20, 30, and 40 Gy) was given in daily fractions of 500 rad to different groups of rabbits. The diaphyseal area of one forearm of each rabbit was irradiated and the other forearm was used as a control. After healing, the mechanical strength of each ulna was measured. The end point is defined as "strength reduction dose-63" (SRD63), i.e., the dose which would be expected to reduce the mechanical strength of the irradiated, fractured, and healed bone compared with the contralateral unirradiated diaphysis by 63%. The SRD63's for preoperative and postoperative radiotherapy were 4350 rad (43.5 Gy) and 6200 rad (62 Gy), respectively, with a 500 rad (5 Gy)/fraction schedule. Through the use of the nominal standard dose (NSD) formula at 300 rad (3 Gy)/fraction and five fraction per week, these SRD63's are equivalent to 5700 rad (57 Gy) and 8100 rad (81 Gy), respectively.