Micro-CT Analysis of Radiation-Induced Osteopenia and Bone Hypovascularization in Rat

Treatment of carcinomas of the upper aerodigestive tract often requires external radiation therapy. However, radiation affects all the components of bone, with different degrees of sensitivity, and may produce severe side effects such as mandibular osteoradionecrosis (ORN). Intraosseous vascularization is thought to be decreased after irradiation, but its impact on total bone volume is still controversial. The aim of this study was to compare intraosseous vascularization, cortical bone thickness, and total bone volume in a rat model of ORN versus nonirradiated rats, using a micro-computed tomography (micro-CT) analysis after intracardiac injection of a contrast agent. The study was performed on 8-week-old Lewis 1A rats (n = 14). Eleven rats underwent external irradiation on the hind limbs by a single 80-Gy dose. Three rats did not receive irradiation and served as controls for statistical analysis. Eight weeks after the external irradiation, all the animals received a barium sulfate intracardiac injection under general anesthesia. All samples were analyzed with the micro-computed tomography system at a resolution of 5.5 μm. The images were later processed to create 3D reconstructions and study vascularization, bone volume, and cortical thickness. Data from irradiated and nonirradiated rats were compared using the Kruskal-Wallis test. No animal died after irradiation. Nineteen irradiated tibias and six nonirradiated tibias were included for micro-CT analysis. The vessel percentage was significantly lower in irradiated bones (p = 0.0001). The distance between the vessels, a marker of vascular destruction, was higher after irradiation (p = 0.001). The vessels were also more altered distally after irradiation (p = 0.028). Cortical thickness was severely decreased after irradiation, sometimes even reduced to zero. Both trabecular and cortical structures were destroyed after irradiation, with wide bone gaps. Finally, both total bone volume (p = 0.0001) and cortical thickness (p = 0.0001) were significantly decreased in irradiated tibias compared to nonirradiated tibias. These results led to multiple spontaneous fractures in the irradiated group, and the destruction of intraosseous vessels observed macroscopically with the radiographic preview. This study revealed the impact of radiation on intraosseous vasculature and cortical bone with a micro-CT analysis in a rat ORN model. Hypovascularization and osteopenia are consistent with the literature, contributing a morphological scale with high resolution. Visualization of the vasculature by micro-CT is an innovative technique to see the changes after radiation, and should help adjust bone tissue engineering in irradiated bone.