Intensity modulated radiation therapy (IMRT) is often used for the treatment of soft tissue sarcoma. Due to high radiation doses, many patients have high risk of suffering from a femoral bone fracture sometime following the IMRT treatment The most common type of radiation treatment-related fracture is a stress fracture. The fracture risk rate may be as high as 24% in sarcoma patients who have undergone periosteal stripping and received chemotherapy. Thus, it is necessary to be able to identify those patients with high risk for IMRT treatment-related bone fracture. In this paper, we will first present IMRT treatment planning techniques. We will then discuss how bone system changes their stiffness and how the fracture risk develops after a certain period of time post radiation treatment. Finally, we will present our latest data on the femoral bone fracture risk factor assessment for patients with soft tissue sarcoma following IMRT treatment. We have developed a novel mathematical model of trabecular bone composed of a disordered cubic network. Based on our preliminary data, we believe that this new mathematical model could shed new light on the relationship between the femoral bone fracture risk factor and the radiation dose delivered by an IMRT plan and provide a valuable prognostic tool for these high-risk patients.