Post-radiation fractures after radiotherapy are prevalent in specific anatomic locations, such as the pelvis following urologic or gynecologic cancer treatment, and may lead to devastating complications including amputation in extremity sites such as the femur after treatment for soft-tissue sarcoma. Lack of progress in developing strategies for prevention or treatment is limited by poor understanding of underlying pathophysiology. While altered histologic (early increased, later decreased osteoclastic bone turnover) and structural (trabecular bone loss) properties of irradiated bone have been described, CT and DXA clinical scans are often normal and fail to predict fracture risk. Preliminary animal model work suggests irradiated bone behaves in an embrittled fashion and that it is in fact compositional parameters that cause this brittle behavior. This proposal focuses on two bone compositional changes, their relationship to biomechanical changes, and the translational potential to favorably alter those compositional changes with consequent improvement in biomechanical properties of irradiated bone. This proposal builds upon our lab's track record of using small animal hind limb irradiation models to study post-radiation growth plate pathophysiology combined with preliminary data supportive of each current hypothesis. The animal model to be used has been well characterized with respect to the histologic, vascular, and structural changes, which recapitulate findings in human retrieval irradiated specimens. Aim 1 investigates the effects of irradiation of bone using a focal irradiation model on collagen cross-linking, altered crystallinity, and altered mineral:matrix ratio compared to non-irradiated bone via Raman spectroscopy. In Aim 2, we explore whether irradiated bone accumulates advanced glycation end products (AGEs) over time at a slower rate than chemical cross-link changes observed in Raman endpoints, in a dose dependent fashion, and also most prominently at the metaphyseal endosteal surface. In Aim 3, the biomechanical properties of the bone material and bone structure are assessed to determine if loss in material and functional properties correspond to changes in collagen/mineral and AGEs. In Aim 4, we test whether a radioprotectant (amifostine), anabolic agent (PTH), or anti-resorptive agent (bisphosphonate) are capable of decreasing post-radiation collagen and AGE alterations as well as maintain bone biomechanics. Given the current lack of understanding of post-radiation fractures and the availability of potentially translatable therapies, the potential for clinical impact is high. Furter, non-invasive Raman techniques are being developed as a means of fracture risk prediction that may prove useful in following irradiated bones.