From what I know, robotic brain surgery has been tried before and there currently are robots that are used in this capacity. The difference between brain surgery and other soft tissue surgery is that there are hard endpoints in the skull that computers can map and define. This is in contrast to the prostate for example that is just a mess of ever shifting organs, vessels and tissues. This makes it impossible for a computer to map and follow a precise pre-set pattern unlike in the cranium. Therefore, this hasn't been an area where ISRG has found a market. THis all could change of course and I am not sure what patents are owned in this particular area. Hope that helps a bit.