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@ARTICLE{Harris:170001,
      author       = {T. C. 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        = {{I}mprovements in beam's eye view fiducial tracking using a
                      novel multilayer imager.},
      journal      = {Physics in medicine and biology},
      volume       = {66},
      number       = {15},
      issn         = {1361-6560},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2021-01700},
      pages        = {155007},
      year         = {2021},
      note         = {#EA:E041#},
      abstract     = {Purpose.Electronic portal image devices (EPIDs) have been
                      investigated previously for beams-eye view (BEV)
                      applications such as tumor tracking but are limited by low
                      contrast-to-noise ratio and detective quantum efficiency. A
                      novel multilayer imager (MLI), consisting of four stacked
                      flat-panels was used to measure improvements in fiducial
                      tracking during liver stereotactic body radiation therapy
                      (SBRT) procedures compared to a single layer
                      EPID.Methods.The prototype MLI was installed on a clinical
                      TrueBeam linac in place of the conventional DMI single-layer
                      EPID. The panel was extended during volumetric modulated arc
                      therapy SBRT treatments in order to passively acquire data
                      during therapy. Images were acquired for six patients
                      receiving SBRT to liver metastases over two fractions each,
                      one with the MLI using all 4 layers and one with the MLI
                      using the top layer only, representing a standard EPID. The
                      acquired frames were processed by a previously published
                      tracking algorithm modified to identify implanted radiopaque
                      fiducials. Truth data was determined using respiratory
                      traces combined with partial manual tracking. Results for 4-
                      and 1-layer mode were compared against truth data for
                      tracking accuracy and efficiency. Tracking and noise
                      improvements as a function of gantry angle were
                      determined.Results. Tracking efficiency with 4-layers
                      improved to $82.8\%$ versus $58.4\%$ for the 1-layer mode, a
                      relative improvement of $41.7\%.$ Fiducial tracking with
                      1-layer 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. The
                      reduction in noise correlated with an increase in
                      successfully tracked frames (r = 0.913) and with increased
                      tracking accuracy (0.927).Conclusion. Increases in MV photon
                      detection efficiency by utilization of a MLI results in
                      improved fiducial tracking for liver SBRT treatments. Future
                      clinical applications utilizing BEV imaging may be enhanced
                      by including similar noise reduction strategies.},
      keywords     = {EPID (Other) / beams eye view (Other) / tumor tracking
                      (Other)},
      cin          = {E041},
      ddc          = {530},
      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:34233309},
      doi          = {10.1088/1361-6560/ac1246},
      url          = {https://inrepo02.dkfz.de/record/170001},
}