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@ARTICLE{Martisikova:136762,
      author       = {M. Martisikova$^*$ and T. Gehrke$^*$ and S. Berke$^*$ and
                      G. Aricò$^*$ and O. Jäkel$^*$},
      title        = {{H}elium ion beam imaging for image guided ion
                      radiotherapy.},
      journal      = {Radiation oncology},
      volume       = {13},
      number       = {1},
      issn         = {1748-717X},
      address      = {London},
      publisher    = {BioMed Central},
      reportid     = {DKFZ-2018-01200},
      pages        = {109},
      year         = {2018},
      abstract     = {Ion beam radiotherapy provides potential for increased dose
                      conformation to the target volume. To translate it into a
                      clinical advantage, it is necessary to guarantee a precise
                      alignment of the actual internal patient geometry with the
                      treatment beam. This is in particular challenging for inter-
                      and intrafractional variations, including movement. Ion
                      beams have the potential for a high sensitivity imaging of
                      the patient geometry. However, the research on suitable
                      imaging methods is not conclusive yet. Here we summarize the
                      research activities within the 'Clinical research group
                      heavy ion therapy' funded by the DFG (KFO214). Our aim was
                      to develop a method for the visualization of a 1 mm
                      thickness difference with a spatial resolution of about
                      1 mm at clinically applicable doses.We designed and built a
                      dedicated system prototype for ion radiography using
                      exclusively the pixelated semiconductor technology Timepix
                      developed at CERN. Helium ions were chosen as imaging
                      radiation due to their decreased scattering in comparison to
                      protons, and lower damaging potential compared to carbon
                      ions. The data acquisition procedure and a dedicated
                      information processing algorithm were established. The
                      performance of the method was evaluated at the ion beam
                      therapy facility HIT in Germany with geometrical phantoms.
                      The quality of the images was quantified by
                      contrast-to-noise ratio (CNR) and spatial resolution (SR)
                      considering the imaging dose.Using the unique method for
                      single ion identification, degradation of the images due to
                      the inherent contamination of the outgoing beam with light
                      secondary fragments (hydrogen) was avoided. We demonstrated
                      experimentally that the developed data processing increases
                      the CNR by $350\%.$ Consideration of the measured ion track
                      directions improved the SR by $150\%.$ Compared to proton
                      radiographs at the same dose, helium radiographs exhibited
                      $50\%$ higher SR (0.56 ± 0.04lp/mm vs.
                      0.37 ± 0.02lp/mm) at a comparable CNR in the middle of
                      the phantom. The clear visualization of the aimed
                      inhomogeneity at a diagnostic dose level demonstrates a
                      resolution of 0.1 g/cm2 or $0.6\%$ in terms of
                      water-equivalent thickness.We developed a dedicated method
                      for helium ion radiography, based exclusively on pixelated
                      semiconductor detectors. The achievement of a clinically
                      desired image quality in simple phantoms at diagnostic dose
                      levels was demonstrated experimentally.},
      cin          = {E040},
      ddc          = {610},
      cid          = {I:(DE-He78)E040-20160331},
      pnm          = {315 - Imaging and radiooncology (POF3-315)},
      pid          = {G:(DE-HGF)POF3-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:29898746},
      pmc          = {pmc:PMC6000951},
      doi          = {10.1186/s13014-018-1046-6},
      url          = {https://inrepo02.dkfz.de/record/136762},
}