Welcome to OCF! Im glad you have found our group
Its always nice having survivors join our ranks.
Please understand our site is made up of survivors/patients and caregivers. We do not have medical backgrounds, years of medical school and training. Doctors have the patients chart, history and the patient right in front of them, plus all the previously mentioned characteristics. We always speak from experience but what one patient goes thru another may not (even with the same history and the tumor exactly the same).
I have done many HBO dives. As far as HBO working on scar tissue, I have not used it for that. Nor have I seen any other HBO patients there for scarring. I vaguely remember another HBO patient had severe swelling of her ankles and did HBO to help with it. Im sorry my memory is not what it used to be and I cant remember much about her case besides she was in the next HBO chamber with her swollen lags. I used HBO to help heal post radiation slow healing wounds. Being 20 months post rads, most of your recovery is already behind you. In my opinion, I dont think HBO would be something that can help you. Ive seen at the pharmacy creams that claim to fix scars and wrinkles but I dont know if they work. I wouldnt buy any of them until I checked with at least one of my doctors. From everything Ive learned here, Im sorry to say the scarring may not improve unless thru surgery. Even that is risky! Having surgery in an area where it was previously radiated may not be an option as it would have compromised healing abilities.
A SLP or dietitian can have you complete a barium swallow test to first determine how well and what you are physically able to swallow. Many members have found improvements thru physical therapy with helping them to identify their swallowing capabilities. Some patients need to have their esophagus stretched with surgery using balloons. Usually these patients require at least 2 stretches before it helps them. They also need periodic stretches for their throat to remain open.
Im very sorry you are having late stage complications from your treatments. Oral cancer (OC) is a brutal disease with barbaric treatments and seemingly never ending recoveries. Its a rare patient that we see who does not have any issues after their treatments. You have been thru enough and Im sure it was no easy battle. It just doesnt seem fair that any other issues would bother you. I think your medical team is the very best place to get help with your issues. You were treated at one of the countrys top CCCs. They should have an entire team able to assist you with any after treatment problems you may encounter. Im wishing you all the very best with this.
Maybe something in the Treatment link or the Recovery Complications link could help you with more info.
Best wishes!
OCF main site --- TREATMENT Main OCF site -- Recovery Complications 
