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@ARTICLE{Titt:127645,
      author       = {U. Titt and M. Sell and J. Unkelbach and M. Bangert$^*$ and
                      D. Mirkovic and U. Oelfke and R. Mohan},
      title        = {{D}egradation of proton depth dose distributions
                      attributable to microstructures in lung-equivalent
                      material.},
      journal      = {Medical physics},
      volume       = {42},
      number       = {11},
      issn         = {0094-2405},
      address      = {New York, NY},
      reportid     = {DKFZ-2017-03668},
      pages        = {6425 - 6432},
      year         = {2015},
      abstract     = {The purpose of the work reported here was to investigate
                      the influence of sub-millimeter size heterogeneities on the
                      degradation of the distal edges of proton beams and to
                      validate Monte Carlo (MC) methods' ability to correctly
                      predict such degradation.A custom-designed high-resolution
                      plastic phantom approximating highly heterogeneous,
                      lung-like structures was employed in measurements and in
                      Monte Carlo simulations to evaluate the degradation of
                      proton Bragg curves penetrating heterogeneous
                      media.Significant differences in distal falloff widths and
                      in peak dose values were observed in the measured and the
                      Monte Carlo simulated curves compared to pristine proton
                      Bragg curves. Furthermore, differences between simulations
                      of beams penetrating CT images of the phantom did not agree
                      well with the corresponding experimental differences. The
                      distal falloff widths in CT image-based geometries were
                      underestimated by up to 0.2 cm in water (corresponding to
                      0.8-1.4 cm in lung tissue), and the peak dose values of
                      pristine proton beams were overestimated by as much as
                      $˜35\%$ compared to measured curves or depth-dose curves
                      simulated on the basis of true geometry. The authors
                      demonstrate that these discrepancies were caused by the
                      limited spatial resolution of CT images that served as a
                      basis for dose calculations and lead to underestimation of
                      the impact of the fine structure of tissue heterogeneities.
                      A convolution model was successfully applied to mitigate the
                      underestimation.The results of this study justify further
                      development of models to better represent heterogeneity
                      effects in soft-tissue geometries, such as lung, and to
                      correct systematic underestimation of the degradation of the
                      distal edge of proton doses.},
      keywords     = {Protons (NLM Chemicals)},
      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:26520732},
      pmc          = {pmc:PMC4608968},
      doi          = {10.1118/1.4932625},
      url          = {https://inrepo02.dkfz.de/record/127645},
}