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@ARTICLE{Frick:299569,
      author       = {S. Frick and M. Schneider and D. Thorwarth$^*$ and R.-P.
                      Kapsch},
      title        = {{D}etermination of output correction factors in magnetic
                      fields using two methods for two detectors at the central
                      axis.},
      journal      = {Physics in medicine and biology},
      volume       = {70},
      number       = {6},
      issn         = {0031-9155},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2025-00510},
      pages        = {065008},
      year         = {2025},
      abstract     = {Objective.Commissioning an MR-linac treatment planning
                      system requires output correction
                      factors,kB→,Qclin,Qmsrfclin,fmsr, for detectors to
                      accurately measure the linac's output at various field
                      sizes. In this study,kB→,Qclin,Qmsrfclin,fmsrwas
                      determined at the central axis using two methods: one that
                      combines the corrections for the influence of the magnetic
                      field and the small field in a single factor
                      (kB→,Qclin,Qmsrfclin,fmsr), and a second that isolates the
                      magnetic field's influence, allowing the use of output
                      correction factors without a magnetic
                      field,kQclin,Qmsrfclin,fmsr, from literature for
                      determiningkB→,Qclin,Qmsrfclin,fmsr.Approach.To
                      determinekB→,Qclin,Qmsrfclin,fmsrand examine its behaviour
                      across different photon energies and magnetic flux
                      densitiesBin small fields, measurements with an ionization
                      chamber (0.07 cm3sensitive volume) and a solid-state
                      detector were carried out at an experimental facility for
                      both approaches. Changes in absorbed dose to water with
                      field size were determined via Monte Carlo simulations. To
                      evaluate clinical applicability, additional measurements
                      were conducted on a 1.5 T MR-linac.Main results.Both methods
                      determined comparablekB→,Qclin,Qmsrfclin,fmsrresults. For
                      field sizes >3 × 3 cm2,Branging from -1.5 to 1.5 T and
                      photon energies of 6 and 8 MV, no change
                      ofkQclin,Qmsrfclin,fmsras a function of the magnetic field
                      was observed. Comparison with measurement results from the
                      1.5 T MR-linac confirm this. For ⩽3 × 3
                      cm2,kB→,Qclin,Qmsrfclin,fmsrdepends on photon energy andB.
                      For 1.5 T and 6 MV,BreduceskQclin,Qmsrfclin,fmsrup to $3\%$
                      for the ionization chamber and up to $7\%$ for the
                      solid-state
                      detector.Significance.kB→,Qclin,Qmsrfclin,fmsrwere
                      successfully determined for two detectors, enabling their
                      use at a 1.5 T MR-linac. For field sizes of >3 × 3
                      cm2,kB→,Qclin,Qmsrfclin,fmsris one for most detectors
                      suitable for small field dosimetry for all available
                      perpendicular MR-linac systems, as confirmed in the
                      literature. For these field sizes and detectors, the
                      correction factor accounting for the dosimeter response
                      change in the reference field due to the magnetic
                      field,kB→,Qmsrfmsr, can be used for cross-calibration.
                      Therefore, future research may only focus on small field
                      sizes.},
      keywords     = {Magnetic Fields / Radiometry: instrumentation / Monte Carlo
                      Method / Particle Accelerators: instrumentation / Magnetic
                      Resonance Imaging: instrumentation / MR-guided radiation
                      therapy (Other) / magnetic field correction factor (Other) /
                      output correction factor (Other) / small field dosimetry
                      (Other)},
      cin          = {TU01},
      ddc          = {530},
      cid          = {I:(DE-He78)TU01-20160331},
      pnm          = {899 - ohne Topic (POF4-899)},
      pid          = {G:(DE-HGF)POF4-899},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:39983310},
      doi          = {10.1088/1361-6560/adb934},
      url          = {https://inrepo02.dkfz.de/record/299569},
}