I did a variation on another member's recipe. I boiled my fresh or frozen cranberries in a small amount of water without sugar until they popped, I then strained them through a sieve. You can then add water if the taste is too strong.
Make sure you are getting the right amount of water in your bladder for the RT session. I know for a fact that on occasions my bladder was empty during treatment yet it still went ahead. I know the bladder was empty because my catheter tap was left open.
My problems started 3/4 months post SRT, the first sign was losing lots of debris and blood clots. There are very few consultants that understand radiation damage, fortunately severe damage is not that common.
Detecting water infections can be difficult, samples are sometimes sent to the lab to be cultured so the correct antibiotics are prescribed.Mine often come back as retest required.
Best wishes with the rest of your treatment.