When I was first diagnosed I investigated the Cyberknife. I am considered a high risk case as well. Cybeknife has a patient website and there are two doctors there who will answer your questions. I posted my statistics and asked if the CK was appropriate for my case. I had a reply within 24 hours. Both said it was not appropriate as a primary but might be used as a "boost". What you have described as your recomendation thus far sounds very much like the "boost" option. You may want to try googling "cyberknife patient support". I can't find the address or I would give you a link.
Good luck with whatever choice you make.
Diagnosed 04/10/08 Age 58 at the time
Gleason 4 + 3
DRE palpable tumor on left side
100% of 12 cores positive for PCa range 35% to 85%
Bone scan clear and chest x ray clear
CT scan shows potential lymph node involvement in pelvic region
Started Casodex on May 2 and stopped on June 1, 2008
Lupron injection on May 15 and every four months for next two years
Started IMRT/IGRT on July 10, 2008. 45 treatments scheduled
First 25 to be full pelvic for a total dose of 45 Gray to lymph nodes.
Last 20 to prostate only. Total dose to prostate 81 Gray.
Completed IMRT/IGRT 09/11/08.
PSA 02/08 21.5 at diagnosis
PSA 07/08 .82 after 8 wks of hormones
PSA 10/08 .642 one month after completion of IMRT, 6 months hormone