Not sure about cyberknife since I never had it but I just recently had a Whipple after 8 rounds of chemo and 28 radiation treatments. They had hoped mine would shrink away from the vein and it did indeed shrink by half but never disengaged. At one point my CA 19-9 was as low as 7 but after the biopsy following surgery they found there was still quite a lot of cancer there. They ended up grafting a bovine vein because none of my useable veins was right. I really hope your husband's low CA 19-9 and the shrinkage means they have killed most of the cancer and that you get an answer on your cyberknife question.