1. From the Departments of Radiology (G.M.R., R.D.B.) and Orthopedic Surgery (R.S.), Stanford University Medical Center, 300 Pasteur Dr, Stanford, CA 94305-5105; Department of Radiology, The Permanente Medical Group, Oakland, Calif (S.K.); and Department of Radiation Oncology, Stanford Cancer Institute, Stanford, Calif (A.C.).