Radiation-therapy effects on bone density.

Only limited data are available on the effects of radiation-therapy on the mineral content of the bone of children treated for malignancy. The incidence of osteopenia varies between 8 and 23%, but confounding factors were the use of chemotherapy and the effects of prophylactic cranial irradiation. The factors influencing bone atrophy are no more clearly defined in adults treated for cancer by high dose local radiation-therapy. Pathological observed in patient tissues, indicates a clear role for vascular changes in the development of osteopenia, although there remains some uncertainty as to the effects of osteoblast cell loss. Reduced blood flow in bone is clearly dose-related in experimental animal studies and after single doses of >20 Gy changes in bone mineral content have been found. However, this was only at late times (>/=30 weeks) after irradiation. The relationship between these changes and bone strength remains unproven because of the limited nature of many of the animal studies. Radiation dose fractionation data for rib-fracture in breast cancer patients suggests an alpha/beta ratio is in the range 1.8-2.8 Gy, comparable to values obtained for other late responding normal human tissues. Copyright 2003 Wiley-Liss, Inc.