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@ARTICLE{Bangert:125472,
      author       = {M. Bangert$^*$ and J. Unkelbach},
      title        = {{A}ccelerated iterative beam angle selection in {IMRT}.},
      journal      = {Medical physics},
      volume       = {43},
      number       = {3},
      issn         = {0094-2405},
      address      = {New York, NY},
      reportid     = {DKFZ-2017-01598},
      pages        = {1073 - 1082},
      year         = {2016},
      abstract     = {Iterative methods for beam angle selection (BAS) for
                      intensity-modulated radiation therapy (IMRT) planning
                      sequentially construct a beneficial ensemble of beam
                      directions. In a naïve implementation, the nth beam is
                      selected by adding beam orientations one-by-one from a
                      discrete set of candidates to an existing ensemble of (n -
                      1) beams. The best beam orientation is identified in a time
                      consuming process by solving the fluence map optimization
                      (FMO) problem for every candidate beam and selecting the
                      beam that yields the largest improvement to the objective
                      function value. This paper evaluates two alternative methods
                      to accelerate iterative BAS based on surrogates for the FMO
                      objective function value.We suggest to select candidate
                      beams not based on the FMO objective function value after
                      convergence but (1) based on the objective function value
                      after five FMO iterations of a gradient based algorithm and
                      (2) based on a projected gradient of the FMO problem in the
                      first iteration. The performance of the objective function
                      surrogates is evaluated based on the resulting objective
                      function values and dose statistics in a treatment planning
                      study comprising three intracranial, three pancreas, and
                      three prostate cases. Furthermore, iterative BAS is
                      evaluated for an application in which a small number of
                      noncoplanar beams complement a set of coplanar beam
                      orientations. This scenario is of practical interest as
                      noncoplanar setups may require additional attention of the
                      treatment personnel for every couch rotation.Iterative BAS
                      relying on objective function surrogates yields similar
                      results compared to naïve BAS with regard to the objective
                      function values and dose statistics. At the same time, early
                      stopping of the FMO and using the projected gradient during
                      the first iteration enable reductions in computation time by
                      approximately one to two orders of magnitude. With regard to
                      the clinical delivery of noncoplanar IMRT treatments, we
                      could show that optimized beam ensembles using only a few
                      noncoplanar beam orientations often approach the plan
                      quality of fully noncoplanar ensembles.We conclude that
                      iterative BAS in combination with objective function
                      surrogates can be a viable option to implement automated BAS
                      at clinically acceptable computation times.},
      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:26936695},
      doi          = {10.1118/1.4940350},
      url          = {https://inrepo02.dkfz.de/record/125472},
}