radiation therapy center in Madrid

Because no one has answered as yet, I will give you my personal perspective.
RT after, what appears to be, failed surgery is pretty routine and I imagine that your friend will be in good hands.

Dr Google told me that GenesisCare recently took over an existing Spanish network of oncology centers. There seem to be several such centers in the Madrid area.

Sorry about the delay to answer. I am not reading posts so often for the time being, kind of mental vacation.
I do not have direct references from the Genesis center here, but I actually went there to have a more informed opinion on treatment (they are covered by my insurance). Finally, I opted for surgery. I talked with two ROs, one doing HDB and the other doing SBRT. I was impressed by both of them, they seemed very knowledged and they were very friendly and ready to answer any question.
I only have a direct reference about external radiation in Madrid. A friend of mine with a worrisome diagnostic opted for surgery and adjuvant radiation three months later. He went to Ruber Internacional and he was happy with them. He is fine more than two years later.
I would be thankful for any update about your friend's treatment. I am interested to have some references about SRT in Madrid for just in case, more particulartly about Genesis as my most obvious option.

I went to La Milagrosa in 2016 for another urology problem (kidney stones). I even had a scan done there. Good to know another place for SRT.
Thank you and best wishes for your friend's treatment.