When I had surgery three years ago, two (2) of my close friends had brachytherapy. My gleason was 8, my friends both had gleason 6 diagnosis. My doctors said surgery, their doctors said BT would do the job. They are both doing well today and so am I.
So, if you have a Gleason 6 BT will do the job, possibly with fewer immediate side effects. If you have a more aggressive diagnosis you might have to look at surgery and or some form of radiation.
Good luck in making your decision.