Development of a standardized mucositis and osteoradionecrosis animal model using external radiation

Objectives: Although the side effects of radiation therapy vary from mucositis to osteomyelitis depending on the dose of radiation therapy, to date, an experimental animal model has not yet been proposed. The aim of this study was to develop an animal model for assessing complications of irradiated bone, especially to quantify the dose of radiation needed to develop a rat model. Materials and Methods: Sixteen Sprague-Dawley rats aged seven weeks with a mean weight of 267.59 g were used. Atraumatic extraction of a right mandibular first molar was performed. At one week after the extraction, the rats were randomized into four groups and received a single dose of external radiation administered to the right lower jaw at a level of 14, 16, 18, or 20 Gy, respectively. Clinical alopecia with body weight changes were compared and bony volumetric analysis with micro-computed tomography (CT), histologic analysis with H&E were performed. Results: The progression of the skin alopecia was different depending on the irradiation dose. Micro-CT parameters including bone volume, bone volume/tissue volume, bone mineral density, and trabecular spaces, showed no significant differences. The progression of osteoradionecrosis (ORN) along with that of inflammation, fibrosis, and bone resorption, was found with increased osteoclast or fibrosis in the radiated group. As the radiation dose increases, osteoclast numbers begin to decrease and osteoclast tends to increase. Osteoclasts respond more sensitively to the radiation dose, and osteoblasts are degraded at doses above 18 Gy. Conclusion: A standardized animal model clinically comparable to ORN of the jaw is a valuable tool that can be used to examine the pathophysiology of the disease and trial any potential treatment modalities. We present a methodology for the use of an experimental rat model that incorporates a guideline regarding radiation dose.