You will have no problem finding lots of well meaning people touting their "superfoods" or mind-body therapies or organic pesticide free living as a way to prevent a cancer recurrence. Unfortunately, none of them have been proven to work, but it does make lots of people feel better. Perhaps the "placebo" effect of such anti-cancer beliefs can help, but some of us just have more aggressive cancers. Perhaps I am the foolish one relying upon radiation & chemo but you might ask about CyberKnife as a preventive. I was told I had maximum radiation (72 grays)after my first treatment, but this time was still able to take another 25 Grays after my surgery since CyberKnife is so focused they can literally have the beams dance around the prior areas but still zone in on the tongue. It's not widely available and usually used in brain & prostate cancer TX but my CCC is trying it on me and another Stage IV recurrence patient.
Still congratulations on being able to eat solid food, I am still on the PEG 7 months later in part due to the extra radiation so I can understand your doctor's concerns about quality of life. Another poster here EZJim has had radioactive implants or seeds and he has shared how hard it was. So while you have a very good question, if anybody had an accurate answer they would be up for a Nobel prize instead of selling their books or foods on the internet.