Welcome to this site, you will find lots of fellow sufferers able to give useful advice.
My initial diagnosis way back in 2007 was a bit different from yours, and I wasn't a suitable candidate for seed brachytherapy.
However in 2014 I had salvage HDR brachytherapy at Mount Vernon, and found myself needing tamsulosin, I don't know whether the incontinence was a side effect of the brachytherapy or template biopsies?
Anyway the good news is that this year, about 15 months after treatment, I found myself able to cope without tamsulosin.
Take today for instance, my wife took me out Christmas shopping at 9:30 this morning, we stopped for coffee at 11:30 and I visited the gents.
Then we tackled an out of town shopping site and supermarket getting home at 4, by which time I needed the loo, however a year ago I would have been looking for the loo in every shop we went into. So you may find that your bladder settles down in a year or two.