% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@ARTICLE{Serpa:300276,
      author       = {M. Serpa$^*$ and T. Brandt and S. K. B. Spohn$^*$ and A.
                      Rimner$^*$ and C. Bert},
      title        = {{M}egavoltage intrafraction monitoring and position
                      uncertainty in gimbaled markerless dynamic tumor tracking
                      treatment of lung tumors.},
      journal      = {Medical physics},
      volume       = {52},
      number       = {6},
      issn         = {0094-2405},
      address      = {Hoboken, NJ},
      publisher    = {Wiley},
      reportid     = {DKFZ-2025-00729},
      pages        = {4657-4674},
      year         = {2025},
      note         = {2025 Jun;52(6):4657-4674},
      abstract     = {The clinical realization of markerless dynamic tumor
                      tracking (MLDTT) has prompted a new paradigm shift to
                      intrafraction imaging-based quality assurance (QA). During
                      MLDTT treatment using a gimbaled accelerator, the
                      megavoltage (MV) imager serves as an independent system to
                      leverage real-time intrafraction monitoring. Soft-tissue
                      feature tracking has shown promise for tumor localization in
                      confined MV projections, but studies demonstrating its
                      application in clinical MLDTT treatments are scarse.To
                      validate MV image-based dense soft-tissue feature tracking
                      for intrafraction position monitoring of lung tumors during
                      MLDTT stereotactic body radiotherapy (SBRT), and report on
                      the resolved geometric uncertainty.Ten non-small cell lung
                      cancer (NSCLC) patients underwent MLDTT-SBRT using a
                      commercial gimbal-based system. During treatment,
                      beam's-eye-view (BEV) projection images were captured at
                      ∼3 frames s-1 (fps) using the electronic portal imaging
                      device (EPID). MV sequences were streamed to a research
                      workstation and processed off-line using a purpose-built
                      algorithm, the soft-tissue feature tracker (SoFT). Both the
                      tumor and dynamic field aperture position were automatically
                      extracted in the pan and tilt directions of the gimbaled
                      x-ray head, corresponding to the in-plane lateral and
                      longitudinal direction of the imager, and compared to ground
                      truth manual tracking. The success, percentage of fields
                      producing an output, and performance of MV tracking under
                      the presence/absence of anatomy-related obstruction and
                      multi-leaf collimator (MLC) occlusion were quantified,
                      including three-dimensional conformal (3DCRT) and
                      step-and-shoot intensity modulated radiotherapy (IMRT)
                      deliveries. In addition, the geometric uncertainty of MLDTT
                      treatment was estimated as the difference between field
                      aperture and target center position in the BEV. The standard
                      deviation of systematic (Σ) and random (σ) errors were
                      determined.MV tracking was successful for $89.7\%$ of
                      (unmodulated) 3DCRT fields, as well as $82.4\%$ of
                      (modulated) control points (CPs) and subfields (SFs) for
                      IMRT and field-in-field 3DCRT deliveries. The MV tracking
                      accuracy was dependent on the traversed anatomy, tumor
                      visibility, and occlusion by the MLC. The mean MV tracking
                      accuracy was 1.2 mm (pan) and 1.4 mm (tilt), and a resultant
                      2D accuracy of 1.8 mm. The MV tracking performance within 2
                      mm was observed in $92.1\%$ (pan) and $86.6\%$ (tilt),
                      respectively. The mean aperture-target positional
                      uncertainty smaller than 3 mm/5 mm was observed in
                      $94.4/97.9\%$ (pan) and $89.6/96.7\%$ (tilt) of the time.
                      The group Σ and σ were 0.5 mm/0.8 mm (pan), and 0.7 mm/1.2
                      mm (tilt), compared to 0.3 mm/0.5 mm (pan), and 0.6 mm/0.9
                      mm (tilt) based on the manual ground truth.MV imaging
                      coupled with the soft-tissue feature tracker algorithm
                      constitutes a valuable non-invasive method for independent
                      intrafraction surveillance. Tracking multiple features has
                      shown the potential to improve position estimation,
                      notwithstanding obstruction, and occlusion challenges,
                      facilitating the quantification of the geometric uncertainty
                      of MLDTT treatment.},
      keywords     = {intrafraction monitoring (Other) / markerless dynamic tumor
                      tracking (Other) / megavoltage tracking (Other)},
      cin          = {FR01},
      ddc          = {610},
      cid          = {I:(DE-He78)FR01-20160331},
      pnm          = {899 - ohne Topic (POF4-899)},
      pid          = {G:(DE-HGF)POF4-899},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:40177796},
      doi          = {10.1002/mp.17740},
      url          = {https://inrepo02.dkfz.de/record/300276},
}