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@ARTICLE{Reidel:179541,
      author       = {C.-A. Reidel and F. Horst and C. Schuy and O. Jäkel$^*$
                      and S. Ecker and K. Henkner and S. Brons and M. Durante and
                      U. Weber},
      title        = {{E}xperimental {C}omparison of {F}iducial {M}arkers {U}sed
                      in {P}roton {T}herapy: {S}tudy of {D}ifferent {I}maging
                      {M}odalities and {P}roton {F}luence {P}erturbations
                      {M}easured {W}ith {CMOS} {P}ixel {S}ensors.},
      journal      = {Frontiers in oncology},
      volume       = {12},
      issn         = {2234-943X},
      address      = {Lausanne},
      publisher    = {Frontiers Media},
      reportid     = {DKFZ-2022-00719},
      pages        = {830080},
      year         = {2022},
      abstract     = {Fiducial markers are used for image guidance to verify the
                      correct positioning of the target for the case of tumors
                      that can suffer interfractional motion during proton
                      therapy. The markers should be visible on daily imaging, but
                      at the same time, they should produce minimal streak
                      artifacts in the CT scans for treatment planning and induce
                      only slight dose perturbations during particle therapy. In
                      this work, these three criteria were experimentally
                      investigated at the Heidelberg Ion Beam Therapy Center.
                      Several small fiducial markers with different geometries and
                      materials (gold, platinum, and carbon-coated ZrO2) were
                      evaluated. The streak artifacts on treatment planning CT
                      were measured with and without iMAR correction, showing
                      significantly smaller artifacts from markers lighter than 6
                      mg and a clear improvement with iMAR correction. Daily
                      imaging as X-ray projections and in-room mobile CT were also
                      performed. Markers heavier than 6 mg showed a better
                      contrast in the X-ray projections, whereas on the images
                      from the in-room mobile CT, all markers were clearly
                      visible. In the other part of this work, fluence
                      perturbations of proton beams were measured for the same
                      markers by using a tracker system of several high spatial
                      resolution CMOS pixel sensors. The measurements were
                      performed for single-energy beams, as well as for a
                      spread-out Bragg peak. Three-dimensional fluence
                      distributions were computed after reconstructing all
                      particle trajectories. These measurements clearly showed
                      that the ZrO2 markers and the low-mass gold/platinum markers
                      (0.35mm diameter) induce perturbations being 2-3 times lower
                      than the heavier gold or platinum markers of 0.5mm diameter.
                      Monte Carlo simulations, using the FLUKA code, were used to
                      compute dose distributions and showed good agreement with
                      the experimental data after adjusting the phase space of the
                      simulated proton beam compared to the experimental beam.},
      keywords     = {CMOS pixel sensor (Other) / Monte Carlo simulation (Other)
                      / dose perturbation (Other) / fiducial marker (Other) /
                      image guidance (Other) / proton therapy (Other) / streak
                      artifacts (Other)},
      cin          = {E040},
      ddc          = {610},
      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:35402273},
      pmc          = {pmc:PMC8990863},
      doi          = {10.3389/fonc.2022.830080},
      url          = {https://inrepo02.dkfz.de/record/179541},
}