1. Radiation Safety Research Center, Nuclear Technology Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), Komae, Japan
2. Department of Oncology, Lombardi Comprehensive Cancer Center, and Department of Biochemistry and Molecular and Cellular Biology, Georgetown University Medical Center, Georgetown University, Washington, DC, USA
3. Department of Epidemiology and Biostatistics, School of Medicine, University of California, San Francisco, CA, USA
4. Department of Statistics, Radiation Effects Research Foundation, Hiroshima, Japan