It varies from hospital to hospital and also depends a bit on your internal workings. In our area, alcohol is absolutely forbidden during radical radiotherapy to the pelvic area partly because it introduces gas to the bowel, and gas is the great enemy of RT. When John asked about red wine, he was told in no uncertain terms that no alcohol meant no alcohol - it is also a bladder irritant. He also had to stay off caffeine for the duration and in fact, has never gone back to it although he had a drink as soon as the RT was finished 😂
I know that some hospitals are not so rigid so you should follow the diet sheet you were given or the advice of your radiation team. I also know that sometimes, patients ignore the advice or just treat themselves to a drink at weekends; my personal view is that if we are gifted a treatment by medics who are doing their best to help, we have a responsibility to give ourselves the best chance of success by complying with the rules. But I am a pedant by nature and find it very difficult to not follow rules 🤷🏼♀️
"Life can only be understood backwards; but it must be lived forwards." Soren Kierkegaard
Interestingly, not a word was said about diet or alcohol either during my RT planning session or subsequently. The clinic I'm having my RT at, though, tells me to use an enema every day before my treatment, so perhaps that removes the need?