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@ARTICLE{Pehlivan:307282,
      author       = {J. Pehlivan and E. Beyreuther and F. Horst and M. J. Nasse
                      and J. Pawelke and D. Leichtle and O. Jaekel$^*$ and B.
                      Holzapfel},
      title        = {{E}lectron spin resonance measurements of radiation-induced
                      radicals under conventional and ultra-high dose rate
                      electron irradiation.},
      journal      = {Physics in medicine and biology},
      volume       = {nn},
      issn         = {0031-9155},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2025-02975},
      pages        = {nn},
      year         = {2025},
      note         = {epub},
      abstract     = {Ultra-high dose rate (UHDR) radiotherapy has been shown in
                      preclinical studies to reduce normal tissue toxicity without
                      compromising tumour control, a phenomenon referred to as the
                      Flash effect. The radiochemical and biological mechanisms
                      responsible for this effect remain unclear. This study
                      investigates radical formation and oxygen depletion under
                      UHDR and conventional dose rate (CDR) conditions to gain
                      mechanistic insight.Radical formation was investigated using
                      Electron Spin Resonance (ESR) spectroscopy with both spin
                      trapping and spin probe techniques. Oxygen consumption was
                      monitored continuously during irradiation to complement
                      radical yield measurements. E3 medium containing either spin
                      traps (DMPO, DEPMPO, BMPO) or spin probes (CMH, TMTH, CAT1H)
                      was prepared under hypoxic, physioxic, and normoxic
                      conditions. Irradiations were performed at the Electron
                      Linac for beams with high Brilliance and low Emittance
                      (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
                      with 30 MeV electrons across a broad range of dose rates
                      (0.1 Gy/s -10 5 Gy/s). Spin probe measurements enabled
                      consistent comparisons between CDR and UHDR, revealing a
                      significant dependence of spin concentration on both
                      oxygenation and dose rate. In contrast, spin trapping showed
                      reduced radical yields with decreasing oxygen levels, but no
                      significant dose-rate dependence. Direct comparisons between
                      UHDR and CDR were limited by differences in the decay
                      kinetics of the spin adducts. Oxygen measurements confirmed
                      a reduced oxygen consumption at UHDR, with the extent of
                      depletion strongly dependent on initial oxygen
                      concentration. The results support the hypothesis that UHDR
                      conditions promote radical-radical recombination, shifting
                      the reaction equilibrium and reducing the pool of radicals
                      available to react in the homogeneous chemical phase,
                      particularly with oxygen. The combined application of ESR
                      spin trapping, spin probes, and real-time oxygen
                      measurements offers complementary insight into
                      dose-rate-dependent radical processes.},
      keywords     = {Electron Spin Resonance (ESR) (Other) / FLASH effect
                      (Other) / Oxygen depletion (Other) / Radical-Radical
                      Recombination (Other)},
      cin          = {E040},
      ddc          = {530},
      cid          = {I:(DE-He78)E040-20160331},
      pnm          = {315 - Bildgebung und Radioonkologie (POF4-315)},
      pid          = {G:(DE-HGF)POF4-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:41401511},
      doi          = {10.1088/1361-6560/ae2db6},
      url          = {https://inrepo02.dkfz.de/record/307282},
}