Hi Mike. Welcome
I'm going to take a guess it will be hdr brachy, as the three treatments would be identical to mine. I was in my early 50s so a good bit younger than you, but most 67year olds now a days are in very good health so the difference in age is probably irrelevant.
The side effects are not too bad. The brachy will require an over night stay in hospital, and a general anaesthetic. Not very pleasant but it is only one day out of your life. Pissing a little blood afterward not a big issue.
The ebrt was 15 fractions for me. Plenty of people carry on going to work. I chose not too but I could have. I went in and out of Manchester by motorbike. For me I can not remember any side effects apart from a pain in the arse one night. You might need toilet a bit more urgently, so buy a key for disabled toilets off line, it's about £3 and you are entitled to it.
HT is the biggest problem. Complete loss of libido, not a dreadful problem, you don't miss the sex with no libido, it can be a problem in your relationship though. I reckon my penis has lost a few inches, because of atrophy. I'm sure ANDY62 will post soon, he is an expert on surviving HT. I didn't put on much weight, but I think I gained fat and lost muscle. I was on HT for two years and now off it for six months with hardly any return of libido.
I had no great problem with fatigue. Exercise is important whilst on HT to preserve muscle mass. Walking dog etc should be easy. Personally I've never been a gym bunny, but if you enjoy it then definitely do exercise. I really don't think you will be incapacitated by this.
I was only on HT for two years, if I were told I had to take it for the rest of my life, which happens to people with advanced cancer, I would be hesitant about trying to preserve my life over QoL, but I can handle it for two years.