Hi, I had 20 fractions of salvage RT without HT in July last year. I found it manageable, especially as there were no HT side effects to contend with.
Figuring out the logistics of travelling to and from the treatment centre is worth considering, noting any toilet stops en route just in case.
I was in the treatment room typically up to ten minutes each day, so bladder control is important as they require it full.
After a week or so of treatment, trust a fart less and less so it may be worth sitting down to pee as a precaution.
I didn't have a spacer and I'm no expert so I can't add anything on that.
There should be a planning scan before treatment starts so there will be a Q&A session.
Good luck,
Kev.