1. Department of Radiation Oncology, Stanford Medicine, Palo Alto, CA 94304, USA
2. School of Medicine, University of California, San Francisco, CA 94143, USA
3. Division of Cancer Epidemiology & Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
4. Affiliated Physician, Palo Alto Veterans Affairs Hospital, Palo Alto, CA 94304, USA