Correspondence should be addressed to Gui-Zhi JU, Department of Radiation Biology, School of Public Health, Jilin University, 1163 Xinmin Street, Changchun 130021, Jilin China. Tel: +86(0)4315619443. E-mail: jugz @ mail.jlu.edu.cn.Biographical note of the first author: Gui-Zhi JU, female, born in 1942, MD, majoring in radiation medicine.