I am in 5 wk post SBRT radiation and still have constipation. I know I reached the peak of increasing side effects and now on downslope of decreasing side effects. I eat a very high fiber diet and the only thing I eat at lunch is a big bowl of fruit and drink plenty of liquids. Radiologist suggested Miri Lax and it is supposed to take 1-2 days but after 2 weeks, started to feel the warnings on label of nausea and stomach pain so he said to discontinue. I added a full apple and 5 prunes and it did the trick in a day or so, but not yet consistent results.
I too have a gel spacer and I think that is part of the problem with both constipation and urination issues. Taking 2 generic Flow Max per day 12 hrs apart. Helps with urination, but not constipation. Just 3 more weeks and it will start to deteriorate and hoping that will finally fix both. Might try one of the "blow outs."