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@ARTICLE{Kretschmer:274231,
      author       = {J. Kretschmer and L. Brodbek and C. Behrends and F. Kugel
                      and B. Koska and C. Bäumer$^*$ and J. Wulff and B.
                      Timmermann$^*$ and B. Poppe and H. K. Looe},
      title        = {{C}omprehensive investigation of lateral dose profile and
                      output factor measurements in small proton fields from
                      different delivery techniques.},
      journal      = {Medical physics},
      volume       = {50},
      number       = {7},
      issn         = {0094-2405},
      address      = {College Park, Md.},
      publisher    = {AAPM},
      reportid     = {DKFZ-2023-00517},
      pages        = {4546-4561},
      year         = {2023},
      note         = {2023 Jul;50(7):4546-4561},
      abstract     = {As part of the commissioning and quality assurance in
                      proton beam therapy, lateral dose profiles and output
                      factors have to be acquired. Such measurements can be
                      performed with point detectors and are especially
                      challenging in small fields or steep lateral penumbra
                      regions as the detector's volume effect may lead to
                      perturbations. To address this issue, this work aims to
                      quantify and correct for such perturbations of six point
                      detectors in small proton fields created via three different
                      delivery techniques.Lateral dose profile and output
                      measurements of three proton beam delivery techniques
                      (pencil beam scanning, pencil beam scanning combined with
                      collimators, passive scattering with collimators) were
                      performed using high-resolution EBT3 films, a PinPoint 3D
                      31022 ionization chamber, a microSilicon diode 60023 and a
                      microDiamond detector 60019 (all PTW Freiburg, Germany).
                      Detector specific lateral dose response functions K(x,y)
                      acting as the convolution kernel transforming the
                      undisturbed dose distribution D(x,y) into the measured
                      signal profiles M(x,y) were applied to quantify
                      perturbations of the six investigated detectors in the
                      proton fields and correct the measurements. A signal
                      theoretical analysis in Fourier space of the dose
                      distributions and detector's K(x,y) was performed to aid the
                      understanding of the measurement process with regard to the
                      combination of detector choice and delivery
                      technique.Quantification of the lateral penumbra broadening
                      and signal reduction at the fields center revealed that
                      measurements in the pencil beam scanning fields are only
                      compromised slightly even by large volume ionization
                      chambers with maximum differences in the lateral penumbra of
                      0.25 mm and $4\%$ signal reduction at the field center. In
                      contrast, radiation techniques with collimation are not
                      accurately represented by the investigated detectors as
                      indicated by a penumbra broadening up to 1.6 mm for passive
                      scattering with collimators and 2.2 mm for pencil beam
                      scanning with collimators. For a 3 mm diameter collimator
                      field, a signal reduction at field center between $7.6\%$
                      and $60.7\%$ was asserted. Lateral dose profile measurements
                      have been corrected via deconvolution with the corresponding
                      K(x,y) to obtain the undisturbed D(x,y). Corrected output
                      ratios of the passively scattered collimated fields obtained
                      for the microDiamond, microSilicon and PinPoint 3D show
                      agreement better than $0.9\%$ (one standard deviation) for
                      the smallest field size of 3 mm.Point detector perturbations
                      in small proton fields created with three delivery
                      techniques were quantified and found to be especially
                      pronounced for collimated small proton fields with steep
                      dose gradients. Among all investigated detectors, the
                      microSilicon diode showed the smallest perturbations. The
                      correction strategies based on detector's K(x,y) were found
                      suitable for obtaining unperturbed lateral dose profiles and
                      output factors. Approximation of K(x,y) by considering only
                      the geometrical averaging effect has been shown to provide
                      reasonable prediction of the detector's volume effect. The
                      findings of this work may be used to guide the choice of
                      point detectors in various proton fields and to contribute
                      towards the development of a code of practice for small
                      field proton dosimetry. This article is protected by
                      copyright. All rights reserved.},
      keywords     = {lateral penumbra (Other) / output factors (Other) / proton
                      fields (Other) / small field dosimetry (Other) / volume
                      effect (Other)},
      cin          = {ED01},
      ddc          = {610},
      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:36908165},
      doi          = {10.1002/mp.16357},
      url          = {https://inrepo02.dkfz.de/record/274231},
}