GREY'S ANATOMY - "Give Peace a Chance" - When Isaac, the hospital lab tech, has an inoperable tumor wrapped around his spine, he turns to Dr. Derek Shepherd to do the impossible, and Derek tests the Chief's authority when Richard objects to moving forward with the risky surgery, on "Grey's Anatomy," THURSDAY, OCTOBER 29 (9:00-10:01 p.m., ET) on the ABC Television Network. (ABC/KAREN NEAL) SANDRA OH, PATRICK DEMPSEY