@carlsbadguy
Yes, I found info about exercise and RT in several places. In some papers it was suggested that exercise in general helps with RT results regardless of the timing. What is important is to help blood get extra oxygenated so it provides oxidative stress to cells. I also found out information about blood actual levels of oxygen after exercise and to my surprise blood stays extra oxygenated for several hours or more, even for the whole day (depending of intensity of exercise). Since cancer cells continue to die off for days and even months after RT is finished, I think that having extra oxygen at any point is beneficial, and if oxygenation last for 24 hours than even exercising day before has benefits.
Also, as you said yourself, doing that level of exercise with overfull bladder is really almost impossible for most people. I mean, I would not be able to do that and neither can my husband - bladder is full to the point of discomfort even when one just sits or is lying down 😬.
If you can, by all means follow advice form your book, but if not, it is comforting yo know that exercising at any point has benefits and helps with oxygenation, hormone distribution, immunity boosting etc etc. 👍