One week of IMRT for recurrent PCa - issue with empty rectum

I started IMRT last week for a local recurrence (small nodule in prostatic fossa detected by DRE, PET PSMA and MRI scans; PSA is 0.11). Five treatment sessions so far and no side effects. The big challenge, which was really downplayed in the pre-RT instructions, is not having a full rectum (gas and solids). I’ve got the bladder filling down, and that is all good if the clinic stays on schedule (yesterday they were running 40 minutes behind). Today, the radiation therapist told me that my rectum had too much gas and that down the line, that would lead to diarrhea. I have a BM every morning like clockwork and then don’t eat before the treatment. She said to try for a BM again an hour before my appointment. I told her that I tried that last week, and the result was that my rectum was then too full of solids (no BM), and I didn’t receive a treatment that day. She then said I might need to alter my diet. I’m a para-vegan (no dairy, and no meat other than skinless chicken breast). I consume a whole grains/food diet and do not eat sugar nor ultra-processed foods. My diet is pretty much in accordance with all the dietary recommendations, and then some.

So, I’m a bit frustrated with situation. First, it would have been helpful to be informed of this issue before starting treatment so that I could have attempted some adjustments. Second, the dietician is recommending one thing and the radiation therapist something else. There is a lack of coordination on top of the lack of advanced information. I recall pressing a nurse about the BM issue and all she said was to have a daily BM before each session and I would be fine. Well, I have done that and apparently, the situation is not fine.

I have a consult with my RO tomorrow and will discuss this issue and get her take on it. In the meantime, I’d appreciate any feedback/shared experiences/solutions that worked. I’ll do my best to get this dialed in but there only seems to be so much I can do at this point. I might start be cutting beans out of my diet, or greatly reducing them.

Many thanks for sharing your thoughts and experiences.

M