Annabel, HBO is Hyperbaric Oxygen treatments. Although used for many different reasons, oral cancer patients are treated to improve blood flow to radiated bone when, for example, a tooth is pulled. The intense oxygen atmosphere causes new capillaries to form, thus increasing the blood flow and healing to the affected area, which is done to prevent the much feared osteoradionecrosis -- death of bone due to radiation. As far as I know, this is the only time it is applicable to oral cancer patients. My HMO referred me to the hospital with the HBO chambers, and covered the entire cost.