Is it possible that you could give us a few more details about your uncle's test results, in particular his PSA reading and Gleason score at diagnosis.
This may sound a silly question but did they operate to remove his prostate or was this a procedure for something else as it is unusual to carry out an operation to remove the prostate at his age. If he had prostate surgery recently then it would be unlikely that he would have radiotherapy so soon.
It sounds as though there might be some misunderstanding about the information you have been given.
Please double check the information and get back to us as there are some very well informed people on this site who can help you to give the necessary support to your uncle.
If you want to read up on the radiotherapy treatment and possible side effects then have a look at the Toolkit on this site.
Your uncle is lucky to have you looking out for him.
We will await further information from you.