Introduction: Radiation-induced osteomyelitis or osteoradionecrosis of the jaw bone is one of the most severe adverse effects of radiotherapy sometimes experienced by head and neck cancer patients. We report on the observed radiographic changes after proton radiotherapy for a patient with squamous cell carcinoma in the mandibular bone.
Case Report: We report on a case of a deeply infiltrating squamous cell carcinoma in the mandible and treated with the proton beam radiotherapy. We describe the radiographic changes of the mandible after proton beam therapy. Primary lesion disappeared and the obvious resorption of the left mandible was observed. However, the images after proton beam therapy showed continued new bone formation and regeneration of the cortical bone of the mandible.
Conclusion: This case illustrates the new bone formation and regeneration of the cortical bone of the mandible after the proton beam radiotherapy. Careful observations in more cases need to verify whether the effect of the proton beam radiotherapy maintaining a given dose while decreasing unnecessary dose to surrounding normal tissue is demonstrated or not.

Keywords: Bone regeneration, Osteoradionecrosis, Proton beam radiotherapy, Radiation-induced osteomyelitis