1. Department of Radiology, Massachusetts General Hospital, Boston
2. Group Health Research Institute, Seattle, Washington
3. Departments of Medicine and Epidemiology and Biostatistics, University of California, San Francisco, San Francisco
4. Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Dartmouth College, Lebanon, New Hampshire
5. Group Health Research Institute, Seattle, Washington5Department of Public Health Sciences, School of Medicine, University of California, Davis