Watching what my partner is going through now after receiving radiotherapy in 2001, if I were in your place and it it's on offer I would go for surgery.
My partner is now 80 and after being told he'd probably be dead by the time the prostate cancer does its thing, he went for radiotherapy.
I'm told once radiotherapy is done the prostate is very difficult to remove so you may not be able to change your mind and have surgery later.
Now my partner has a t4 tumour and it has pushed into both of his uretas which nearly killed him in March. His GFR was 3 and his creatinine at 1000 after I phoned 999. Nobody told us to watch out for this and the signs were there. We just thought it was a stomach bug and now he has kidney damage. This is all after the doc wrote a letter months before saying he needed a nephrostomy (catheter to your kidney) but they didn't have the funding. He was told at the hospital that you can live quite comfortably with 1 kidney....but the inevitable happened and it pushed into his second ureta and it has now lessened his life expectancy despite getting a nephrostomy at the last minute just in time to save his life. 2 weeks after coming out of hospital and losing 13llbs in 8 days, he ended up with ecoli but luckily another 999 call and antibiotics saved him. Not long after he started bleeding from his penis and his bladder now has a spread of cancer in it. He now has another catheter to his bladder called a surpapubic. 80 years old and he has 2 bags to deal with! 1 pure urine and the other urine and blood. He has been bleeding for months andwe told the Mcmillan nurse that he wasn't feeling well. She said ok, I'll arrange a blood test to find out if you're anaemic. A month later and we were still waiting for this blood test. She had forgotten and had we not chased her up he would have carried on getting worse. He's now on iron tablets as he was indeed aneamic from losing a tablespoon of blood every day.
In hindsight and after learning so much about this since March, we have been surrounded by an immense amount of neglect and bad decisions resulting in panic situations and amazing people at the hospital having to save his life when it was so so close to being too late.
He is going through hell and he has much much worse to come. If you can, and if it's safe, please avoid all this by having surgery. The downsides of surgery are nothing compared to this. Many people seem to be out the next day.