Two years after Brachytherapy and External Beam Radiation, my husband too has experienced severe radiation Cystitis - all part of the collateral damage was the way our specialists described it.
They had no real suggestions for relief, except to say that it may come and go for quite a while yet.
However, he has had enormous relief (almost wiping out symptoms- albeit temporarily) with a tablet called Voltaren. If you are in Australia, you will know this medication, its normally used for sprains, strains, migraine pain etc. He tried some of this in desperation about 1 year ago, and was absolutely delighted with the results - almost immediate, within half an hour.
Voltaren here in Australia is available over the counter without a prescription. He uses the 25mg tablet called Voltaren Rapid. This allows him at least half a day without all those urinary problems you mentioned, which he too was suffering from (and I DO mean SUFFERING!). He also had blood in his urine, extreme pain on urination, frequency of urination and some incontinence due to the frequency and desperate need to find a toilet fast.
We told our specialists about it, and although they had not heard of Voltaren working in this way for radiation cystitis, they did say that if it is helping, by all means to go ahead and use it. They did warn that long term use MAY cause some stomach irritation and problems, but that did not worry my husband, as it has allowed him to reclaim some of his independence and his life.
He doesn't take them all the time, just when he wants to be out and about for a few hours and away from home. It had made a huge difference to his outlook and the depression that the radiation cystitis was causing.
In case you are not in Australia, and don't know this product, its pharmaceutical name is
Diclofenac Potassium 25mg and here it costs about $15.00 for 30 tablets.
I hope this helps. We do sympathise with you as we know the toll this has taken on my husband. Please check with your own doctor first.