1. From the Departments of Radiology (N.H., M.K., I.B., E.S., M.J.G., I.P.), Medical Physics (H.V.), Epidemiology and Biostatistics (J.Z., M.C.), and Surgery (J.G.A.), Memorial Sloan Kettering Cancer Center, 1275 York Ave, Box 29, New York, NY 10065.