After continuous exposure over 5 weeks to 0.0002 cGy/min radiation (400-fold over background radiation), the exposed mice did not demonstrate increased levels of DNA nucleobase damage (hypoxanthine, 8oxoG, 1,N6-ethenoadenine, or 3,N4-ethenocytosine) or DNA fragmentation (MNT assay and double strand break–induced HR) above background levels. In addition, low dose-rate radiation did not induce Cdkn1a, Gadd45a, Mdm2, Atm, or Dbd2 gene expression before and after irradiation (from Olipitz et al. [93]). The same total dose delivered acutely induced both MN and transcriptional responses.