We probably need a few more details, like his PSA and how it has behaved over the last four years. Whether it is T1,T2,T3 or T4 tumour, my guess is T3 if 5 out of 6 cores are positive. What the Gleason score is? Cribriform patter is considered more likely to be aggressive, perineural invasion is cancer cells in the prostate nerves, but this is not known to be a bad sign.
When I had RT I met someone who was having RT to the throat, it was not nice as swallowing is painful. I don't think he will find prostate cancer treatment as bad as the treatment he has already had for his throat.