The recommendation that he has radiotherapy will have been made by a multi-disciplinary team including urologists (surgeons), oncologists, radiologists and other disciplines. He could get a second opinion to see whether another doctor would disagree with that specialist team and, if he wished, push for surgery regardless. But, and this is a big but, he would need to take into account that the surgery would be unlikely to be effective, he would probably have to have hormone therapy & radiotherapy anyway and so would have to live with both sets of side effects. Also, if the cancer has already broken out of the gland, he would probably not be able to have nerve-sparing surgery which increases his risk of permanent incontinence and also pretty much guarantees erectile dysfunction. At least with HT / RT, there is a chance of maintaining / recovering the ability to have penetrative sex.
It may be that surgery is not being offered because the hospital suspects there is wider spread to his bones or organs and that is why the PET scan is being done. When you see the onco in March, if the PET is clear it would be worth asking about different types of RT such as brachytherapy or a combination of brachy and external radiotherapy.