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@ARTICLE{Nabha:274337,
      author       = {R. Nabha and M. De Saint-Hubert and J. Marichal and J.
                      Esser and O. Van Hoey and C. Bäumer$^*$ and N. Verbeek and
                      L. Struelens and E. Sterpin and K. Tabury and L. Marek and
                      C. Granja and B. Timmermann$^*$ and F. Vanhavere},
      title        = {{B}iophysical characterization of collimated and
                      uncollimated fields in pencil beam scanning proton therapy.},
      journal      = {Physics in medicine and biology},
      volume       = {68},
      number       = {6},
      issn         = {0031-9155},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2023-00543},
      pages        = {064001},
      year         = {2023},
      abstract     = {Objective. The lateral dose fall-off in proton pencil beam
                      scanning (PBS) technique remains the preferred choice for
                      sparing adjacent organs at risk as opposed to the distal
                      edge due to the proton range uncertainties and potentially
                      high relative biological effectiveness. However, because of
                      the substantial spot size along with the scattering in the
                      air and in the patient, the lateral penumbra in PBS can be
                      degraded. Combining PBS with an aperture can result in a
                      sharper dose fall-off, particularly for shallow
                      targets.Approach. The aim of this work was to characterize
                      the radiation fields produced by collimated and uncollimated
                      100 and 140 MeV proton beams, using Monte Carlo simulations
                      and measurements with a MiniPIX-Timepix detector. The dose
                      and the linear energy transfer (LET) were then coupled with
                      publishedin silicobiophysical models to elucidate the
                      potential biological effects of collimated and uncollimated
                      fields.Main results. Combining an aperture with PBS reduced
                      the absorbed dose in the lateral fall-off and out-of-field
                      by $60\%.$ However, the results also showed that the
                      absolute frequency-averaged LET (LETF) values increased by a
                      maximum of 3.5 keVμm-1in collimated relative to
                      uncollimated fields, while the dose-averaged LET (LETD)
                      increased by a maximum of 7 keVμm-1. Despite the higher LET
                      values produced by collimated fields, the predicted DNA
                      damage yields remained lower, owing to the large dose
                      reduction.Significance. This work demonstrated the
                      dosimetric advantages of combining an aperture with PBS
                      coupled with lower DNA damage induction. A methodology for
                      calculating dose in water derived from measurements with a
                      silicon-based detector was also presented. This work is the
                      first to demonstrate experimentally the increase in LET
                      caused by combining PBS with aperture, and to assess the
                      potential DNA damage which is the initial step in the
                      cascade of events leading to the majority of
                      radiation-induced biological effects.},
      keywords     = {Humans / Proton Therapy: methods / Protons / Radiotherapy
                      Planning, Computer-Assisted: methods / Radiotherapy Dosage /
                      Monte Carlo Method / DNA damage (Other) / Timepix (Other) /
                      aperture (Other) / collimation (Other) / pencil beam
                      scanning (Other) / proton therapy (Other) / Protons (NLM
                      Chemicals)},
      cin          = {ED01},
      ddc          = {530},
      cid          = {I:(DE-He78)ED01-20160331},
      pnm          = {899 - ohne Topic (POF4-899)},
      pid          = {G:(DE-HGF)POF4-899},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:36821866},
      doi          = {10.1088/1361-6560/acbe8d},
      url          = {https://inrepo02.dkfz.de/record/274337},
}