Protons are the dominant particles both in galactic cosmic rays and in solar particle events and, furthermore, proton irradiation becomes increasingly used in tumour treatment. It is believed that complex DNA damage is the determining factor for the consequent cellular response to radiation. DNA plasmid pBR322 was irradiated at U120-M cyclotron with 30 MeV protons and treated with two Escherichia coli base excision repair enzymes. The yields of SSBs and DSBs were analysed using agarose gel electrophoresis. DNA has been irradiated in the presence of hydroxyl radical scavenger (coumarin-3-carboxylic acid) in order to distinguish between direct and indirect damage of the biological target. Pure scavenger solution was used as a probe for measurement of induced OH· radical yields. Experimental OH· radical yield kinetics was compared with predictions computed by two theoretical models-RADAMOL and Geant4-DNA. Both approaches use Geant4-DNA for description of physical stages of radiation action, and then each of them applies a distinct model for description of the pre-chemical and chemical stage.

Department of Applied Physics Chalmers University of Technology Fysikgränd 3 Göteborg SE 412 96 Sweden Atominstitut TU Wien Stadionallee 2 1020 Vienna Austria

Department of Applied Physics Chalmers University of Technology Fysikgränd 3 Göteborg SE 412 96 Sweden Department of Radiation Dosimetry Nuclear Physics Institute of the CAS Na Truhlářce 39 64 Prague 180 00 Czech Republic

Department of Biotechnology Institute of Chemical Technology Prague Technická 5 Prague 166 28 Czech Republic

Department of Radiation Dosimetry Nuclear Physics Institute of the CAS Na Truhlářce 39 64 Prague 180 00 Czech Republic

Université de Bordeaux CNRS IN2P3 Centre d'Etudes Nucléaires de Bordeaux Gradignan CENBG Chemin du Solarium BP 120 33175 Gradignan France

Université de Bordeaux CNRS IN2P3 Centre d'Etudes Nucléaires de Bordeaux Gradignan CENBG Chemin du Solarium BP 120 33175 Gradignan France Department of Radiation Dosimetry Nuclear Physics Institute of the CAS Na Truhlářce 39 64 Prague 180 00 Czech Republic

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Clustered DNA Damage Patterns after Proton Therapy Beam Irradiation Using Plasmid DNA

Proton-induced direct and indirect damage of plasmid DNA