Can radiation therapy cure oral cancer?

Sometimes: It depends on the type and stage of the cancer.

Yes: There are defined areas such as floor of the mouth, tongue, gums, retromolar trigone, palate, etc. Combinations of radiation, surgery and chemotherapy are used. Earlier stages have high probability of cure, more extensive stages (even those to lymph nodes) can be cured with combinations of radiation and chemotherapy but to a lesser percentage of probability.

Oropharyngeal CA: Yes. There is recent increase in incidence of human papilloma virus (hpv) related oropharyngeal cancer such as tonsillar cancer in young non smoking male. These cancer can present as fast growing tumor with early spread to the lymph glands. However they are very sensitive to chemoradiation and has high chance of control and cure.