I completed 20 fractions of radiotherapy four weeks ago as, like yourself, my PSA indicated the cancer had returned. My hospital required the bladder to be (partially) full, and 45 minutes prior to treatment had to drink three cups of water. Initially this was okay but as time passed it became a strain to hold it. I reached an agreement with the radiotherapy staff that if the ultrasound showed my bladder was at the top end of the volume required I could pass some - not too difficult as I have full bladder control following my RARP in December 2022, and the relief was immense!
You’ll be guided by the hospital as to whether you need to use a mini enema in advance but you’ll find that your body will not need these. I used one only for the first treatment.
As Kev T says, don’t trust a fart - you’ll find that you pass mucus. Bowels can become loose and staff will advise if this becomes problematic. I was told to use Imodium which was a great help. This will improve when the treatment stops but took me a couple of weeks.
Keep hydrated: at least three litres a day. I switched to decaffeinated tea which counts towards this. I avoided alcohol and fizzy drinks as these can irritate the bladder. I opted to avoid foods that gave me wind although staff told me this wasn’t strictly necessary.
Know where there are toilets on your route home. Even though my journey was only 30 minutes there were times when I was taken relatively short.
It’s all a bit of a nuisance but is worth it. You’ll be fine!