I think the only thing you can do here is look at the probabilities, Bren. Without SABR, there is perhaps a 50% probability that he'll be dead within 5 years. With SABR, that risk will be significantly lowered, and there's a 90% probability that the treatment will be problem-free. A high probability of significant extension to his life and problem-free treatment against a small probability of problems but still the life extension. I know what I'd do!
Best wish,
Chris