Which foods should be avoided during proton treatment

I'm happy with your progress. I myself am loosening my diet restrictions, starting from a couple days before the end of my Disney cruise.
Certainly, I have been more cautious than you are, and the others who have shared their experience, confirming that the diet was only during radiation treatment -- not necessarily before & after as some pharmacists or oncologists may advise. That said, I learned to like/enjoy bland foods when I avoided fried &/or spicy foods, caffeine/carbonated drinks for a couple weeks before & almost four weeks post-radiation. (No harm done, but I wouldn't say mine or my pharmacist & oncologist's approach was the right or best one.)

I have irritable bowel, so this was a big deal for me during my 28 treatment days (ended May 23).

I found that a low FODMAP, low residue diet worked best. Plus, I would often use a glycerin suppository 2 1/2 hours before treatment, and take a couple of Gas-X. I also only ate one meal a day - dinner, to be after the treatment, with the low volume and low residue making it easier to handle.

I used the ChatGPT AI to recommend/reject food choices matching those requirements.

FODMAPs are food ingredients that are not digested by the small intesting, so they go into the large intestine where the bacteria devour them, producing gas. Some people have an issue with them, some don't. Apparently,, I do.

I went off that diet a couple of days ago (just post-radiation series), and my gut scolded me in no uncertain terms.

Why don’t they put everyone on the FODMAP diet for radiation? It just makes so much sense even if you have no IBS issues.
My dietician at Sloan got very defensive (practically scolded me) when I told her I was utilizing this regimen and tried to encourage me to eat foods which were big No-No’s like apples…instant GAS !

What are the diet restrictions, not everyone is aware of what not to eat .

The two posts above yours. Others have posted links and other information, similar to what AI generates. There is no general agreement, if the diet applies during treatments only, or also before and post-treatments. I was advised before-during-snd-after my SBRT: Bland diet, no fried/spicy foods, no gas-causing veggies, eat well-cooked foods. I have received feedbacks that only one that make sense is the advise I got from my pharmacist to stop my herbal drink (it has antioxidants that protect both the healthy and the cancer cells). Why protect the cancer cells that the treatment is trying to kill?

Thank you for replying. A great help and makes sence.
As I said previously with great respect. Not everyone is aware of what is and is not. Thanks again.