title: Detection of γH2AX foci in mouse normal brain and brain tumor after boron neutron capture therapy.
abstract: OBJECTIVE
  In this study, we investigated γH2AX foci as markers of DSBs in normal brain and brain tumor tissue in mouse after BNCT.
  
  
  BACKGROUND
  Boron neutron capture therapy (BNCT) is a particle radiation therapy in combination of thermal neutron irradiation and boron compound that specifically accumulates in the tumor. (10)B captures neutrons and produces an alpha ((4)He) particle and a recoiled lithium nucleus ((7)Li). These particles have the characteristics of extremely high linear energy transfer (LET) radiation and therefore have marked biological effects. High LET radiation causes severe DNA damage, DNA DSBs. As the high LET radiation induces complex DNA double strand breaks (DSBs), large proportions of DSBs are considered to remain unrepaired in comparison with exposure to sparsely ionizing radiation.
  
  
  METHODS
  We analyzed the number of γH2AX foci by immunohistochemistry 30 min or 24 h after neutron irradiation.
  
  
  RESULTS
  In both normal brain and brain tumor, γH2AX foci induced by (10)B(n,α)(7)Li reaction remained 24 h after neutron beam irradiation. In contrast, γH2AX foci produced by γ-ray irradiation at contaminated dose in BNCT disappeared 24 h after irradiation in these tissues.
  
  
  CONCLUSIONS
  DSBs produced by (10)B(n,α)(7)Li reaction are supposed to be too complex to repair for cells in normal brain and brain tumor tissue within 24 h. These DSBs would be more difficult to repair than those by γ-ray. Excellent anti-tumor effect of BNCT may result from these unrepaired DSBs induced by (10)B(n,α)(7)Li reaction.
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Kondo
authors.affiliation: Department of Physiology, Okayama University, Okayama, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Michiue
authors.affiliation: Division of Medical Physics, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Sakurai
authors.affiliation: Division of Medical Physics, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Nakagawa
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Narabayashi
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kinashi
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Masunaga
authors.affiliation: Particle Radiation Oncology Research Center, Research Reactor Institute, Kyoto University, Osaka, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Ono
keywords: Boron neutron capture therapy; DSBs; High LET radiation; γH2AX foci