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@ARTICLE{Stengl:306177,
      author       = {C. Stengl$^*$ and C. Mooshammer$^*$ and P. Haney$^*$ and J.
                      Mahnke$^*$ and L. Rozo-Pardo and A. Stabilini and F. A.
                      Geser and J. Vedelago},
      title        = {{R}oom return effect of secondary neutrons generated by
                      protons, helium, carbon and oxygen ions for radiotherapy.},
      journal      = {Physics in medicine and biology},
      volume       = {70},
      number       = {23},
      issn         = {0031-9155},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2025-02417},
      pages        = {235011},
      year         = {2025},
      note         = {#EA:E040# / Volume 70, Number 23 235011, 2025},
      abstract     = {Secondary neutrons generated during ion beam radiotherapy
                      undergo scattering from treatment room structures. However,
                      their impact for different primary ion species remains
                      insufficiently characterised. Therefore, this study aims to
                      quantify the room return effect of secondary neutrons in
                      radiotherapy for four different primary ion species, namely
                      protons, helium, carbon and oxygen ions, with energies in
                      the range relevant for radiotherapy. Approach. Ambient dose
                      equivalent, H*(10), was measured using three types of rem
                      counters to characterise the neutron field generated by
                      mono-energetic beams of increasing energy of the four
                      primary ions. The rem counters were iteratively placed in
                      four positions around a 30 cm × 30 cm × 30 cm RW3 phantom.
                      Experimental data were compared to Monte Carlo (MC)
                      simulation using a detailed room geometry. Next, the
                      simulation was performed without the room to quantify the
                      room return effect. Main results. MC simulations agreed with
                      the experimental data within the uncertainty ranges. H*(10)
                      decreased with increasing angle relative to the beam
                      direction but increased with higher primary beam energies.
                      Among the ion species studied, oxygen produced the highest
                      values of H*(10) per primary particle, while protons
                      produced the lowest. The room return effect was found to
                      increase with both, the larger angles from the beam axis and
                      the increasing ion energy, ranging from 17 $\%$ up to 83
                      $\%$ of the total H*(10). Significance. This study presents
                      the first quantitative assessment of the room return effect
                      for four primary ion species, protons, helium, carbon, and
                      oxygen, for clinically relevant energies. The results
                      demonstrate that the treatment room itself plays a
                      significant role for H*(10), particularly through
                      contributions from scattered secondary neutrons. Accurate
                      modelling of the room geometry can help improve the
                      reliability of MC imulations and reduce the risk of
                      secondary neutron exposure misestimation during ion beam
                      therapy.},
      keywords     = {Monte Carlo simulations (Other) / ion beam therapy (Other)
                      / rem counter (Other) / secondary neutrons (Other)},
      cin          = {E040},
      ddc          = {530},
      cid          = {I:(DE-He78)E040-20160331},
      pnm          = {315 - Bildgebung und Radioonkologie (POF4-315)},
      pid          = {G:(DE-HGF)POF4-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:41223544},
      doi          = {10.1088/1361-6560/ae1ee6},
      url          = {https://inrepo02.dkfz.de/record/306177},
}