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@ARTICLE{Harris:177234,
      author       = {T. Harris$^*$ and J. Seco$^*$ and D. Ferguson and M.
                      Jacobson and M. Myronakis and I. V. Lozano and M. Lehmann
                      and P. Huber and R. Fueglistaller and D. Morf and H. J.
                      Mamon and J. D. Mancias and N. E. Martin and R. I. Berbeco},
      title        = {{B}eam's-{E}ye-{V}iew {I}maging of {L}iver {SBRT} {W}ith a
                      {N}ovel {M}ulti-{L}ayer {I}mager.},
      journal      = {International journal of radiation oncology, biology,
                      physics},
      volume       = {111},
      number       = {3S},
      issn         = {0360-3016},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {DKFZ-2021-02368},
      pages        = {S47},
      year         = {2021},
      note         = {#EA:E041#},
      abstract     = {Beams-eye view (BEV) imaging during radiation therapy can
                      be used for real-time localization of the treatment target.
                      However, clinical implementation is limited by the poor
                      performance of current electronic portal imaging devices
                      (EPIDs). A novel multilayer imager (MLI), consisting of four
                      stacked conventional flat-panel imagers, was recently shown
                      to have 5.7 times the detective quantum efficiency and
                      nearly 2 times the contrast-to-noise ratio of a conventional
                      EPID. In the current study, we compare the MLI against a
                      single layer imager for the application of fiducial tracking
                      during liver SBRT procedures. The hypothesis is that the MLI
                      will provide more accurate and efficient fiducial
                      tracking.The prototype MLI was installed in the standard MV
                      imager housing on a clinical LINAC, replacing the
                      conventional EPID. The MV imager arm was extended during
                      volumetric modulated arc therapy (VMAT) SBRT treatments for
                      passive data acquisition. Six patients with liver metastases
                      receiving SBRT in 3-5 fractions (900-1200 cGy/fx) were
                      studied. Data was acquired for two fractions of each
                      treatment course, one fraction with the MLI using all 4
                      layers and one with the MLI using the top layer only.
                      Automatic fiducial localization was performed using a
                      modification of a previously published algorithm. Truth data
                      was derived using external surrogate respiratory traces
                      combined with manual tracking. Results for 4- and 1-layer
                      modes were compared against truth data to determine tracking
                      accuracy and efficiency. Tracking and noise improvements
                      were assessed for any correlation.Between 2771 to 6505 image
                      frames were acquired for each patient, with roughly half of
                      each corresponding to acquisition in 1-layer mode and the
                      other half 4-layer mode. Tracking accuracy with the 1-layer
                      imager returned a root mean square error (RMSE) of 2.1 mm
                      compared to 4-layer RMSE of 1.5 mm, a statistically
                      significant (P < 0.001) improvement of 0.6 mm. Successful
                      tracking efficiency with 4 layers improved to $82.8\%$
                      versus $58.4\%$ for the 1-layer mode, a relative improvement
                      of $41.8\%$ (P < 0.001). There was a strong correlation (r =
                      0.913) between the increase in successfully tracked frames
                      and reduction in noise when using the 4-layer mode.Noise
                      reduction and increased MV photon detection efficiency
                      achieved by utilizing a multi-layer MV imager results in
                      improved fiducial tracking for liver SBRT treatments. Future
                      BEV clinical applications may be improved by pursuing
                      similar noise reduction and photon detection enhancement
                      strategies.},
      cin          = {E041},
      ddc          = {610},
      cid          = {I:(DE-He78)E041-20160331},
      pnm          = {315 - Bildgebung und Radioonkologie (POF4-315)},
      pid          = {G:(DE-HGF)POF4-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:34700563},
      doi          = {10.1016/j.ijrobp.2021.07.127},
      url          = {https://inrepo02.dkfz.de/record/177234},
}