Hi Shaun
Sorry to hear of your problem, I am up to my 17th RT session and like you have exlerienced bowel problems due to Radiation irritation, particually towards the end of the week, but fortunately for me I don't have the back or leg pain you suffer.
When I told the Radiotherapist she put me on Imodium tablets and I have found them very good for easing the problem.
I was also instructed by the Oncologist not to have any fibre in my diet so I cannot have brown bread, green veg, green salad or spicy food as these can all add to bowel problems.
Hope this helps and you get your problem sorted soon as I know first hand it can drag you down, and dont forget to keep well hydrated.
All the best
Harley