Mostly, men who are offered RT also Hormone Therapy (HT) or if they don't want or are unsuitable for RT they just are often ordered HT, at least initially. Occasionally, men just have RT, which means it may be less effective but you don't suffer the side effects. I suggest you question whether or not you are being offered HT. RT is painless, just like a prolonged x ray with the same routine follow on each session (called a fraction). The number of fractions you have can vary but will be fewer if a higher dose is given. You need to establish the number of fractions you will be given. RT will be preceded by an appointment where you have miniscule tattoos which aid the Radiographer to align you for RT and possibly more CT scans before treatment to establish how your Prostate moves.
As to whether you should have treatment with potential side effects or just leave the disease to progress hoping something else will take you first, (as death from PCa can be rotten), is something only you can decide. You may be influenced by your general health and whether your father lived long beyond your age. At 85 I am awaiting further Focal Treatment, having refused HT thus far. My Mother and Father lived to 101 and 98 respectively and I hope to live for some years yet, as I am a full time carer for my younger wife.