You need to understand all the salvage options
open to you if SBRT fails. For an overview of all of them, see the table at the bottom of this link:
/pcnrv.blogspot.com/2017/09/focal-salvage-ablation-for-radio.htmlThe best way to salvage is using more radiation or focal ablation, not surgery. For your unfavorable intermediate risk PC, Katz reported 7-yr progression-free probability of 79% - so quite a bit better than
the 58% using surgery.
If you should fail surgery and require salvage radiation, it is successful about
half the time. So your progression free probability comes up to 58% + (42% x 50%) = 79%. If SBRT fails and you get, say salvage SBRT, your progression-free probability would be 79% + (21% x 82%) = 96%
But salvage is only useful if the failure is local and local only. Katz (using SBRT) reports that only about
20% of his failures are local only. Others (using IMRT) report that about
half the failures are local only. This is because SBRT delivers a much higher biologically effective dose than IMRT. At the same time, the dose seen by healthy tissue is quite a bit lower. This is why retreatment is feasible, whereas retreatment with IMRT would not be,
I also think you should explore brachy boost therapy (with either kind of brachytherapy), which has the best reported oncological outcomes for unfavorable intermediate risk. The ASCENDE-RT reported 9-yr biochemical recurrence-free survival (bRFS) of 92% for your risk category, and a retrospective study similarly reported 10-yr bRFS of 94%. The excellent oncological outcomes are associated with increased risk of late-term urinary side effects.
/pcnrv.blogspot.com/2017/05/brachy-boost-therapy-should-be-reserved.html