NTRODUCTION: Giant cell tumor (GCT) is a primary, benign tumor of bone involving long bones, predominantly the distal end of the femur. The most effective treatment for this tumor is surgery. The surgery often involves defect reconstruction following tumor removal. Reconstruction is usually accomplished with cement infilling and in the case of large defects, cement augmentation is also applied in order to prevent post-operative fractures, which is a frequent post-operative complication. Fractures limit the patient’s daily activities and may essence a second operation. Thus, non-invasive methods for prediction of these fractures is of great importance. To date, there is no firm biomechanical data to identify patients at high risk of postoperative fractures for whom stabilization devices to augment bone cement should be employed. METHODS: We present a non-invasive patient-specific approach for predicting bone strength after GCT surgery to identify patients at high risk of postoperative fractures. Our approach consists of quantitative computed tomography (QCT)-based finite element method (FEM) for determining bone strength as a measure of bone fracture. Simpleware (v. 3.1), and ABAQUS (v. 6.10.1) softwares were used in this study to create and analyze the FE models. Voxel-based FE model of distal femur using QCT images was created and validated using in-vitro mechanical testing data. GCT surgery was simulated on a cadaveric mid-shaft to distal femur bone allograft by an orthopedic surgeon. A cavity to simulate tumor removal was created and filled with bone cement. The specimen was then put in a container of water in order to simulate the attenuation of soft tissue and scanned. A calibration phantom (Mindways Software , Inc., San Francisco, CA) was put beneath the container during the scanning. The phantom has 5 tubes with known densities and was used to convert resulting Hounsfield units (HUs) to bone mineral densities (BMDs). After scanning, the specimen was placed in a circular stainless steel fixture and rigidly fixed, and tested in a dynamic testing machine (Model: Hct400/25 ،Zwick/Roellin Germany) under uniaxial compression load applied on the medial condyle via a 25 mm diameter actuator with the displacement control rate of 1 mm/min until failure. This mechanical test was used to validate and verify the FE model. Simpleware scan IP was used to import DICOM images, perform image processing and segment the geometry of bone and cement. The models were imported in Scan FE software for assigning material properties and meshing. Using the data provided by Mindways, a linear equation to convert HUs to BMDs was derived. The geometry was then automatically meshed and a fully voxelised model was created in which each voxel has a BMD corresponding to its greyscale value of the original CT scan images. Heterogeneous material properties for bone and homogenous material properties for cement regions were considered. Linear elastic-perfectly plastic behavior was assumed for bone and linear elastic properties was assigned for cement. Using experimental equations provided in the literature, the BMDs were converted to Young’s modulus and yield strength. Bone densities ranged from 254 to 1620 kg/m3, the elastic moduli from 440 MPa to 14.2 GPa, and yield strength approximately from 21 to 62 MPa. Poisson’s ratio was considered.