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@ARTICLE{Schwahofer:164172,
      author       = {A. Schwahofer$^*$ and P. Mann$^*$ and C. K. Spindeldreier
                      and C. P. Karger$^*$},
      title        = {{O}n the feasibility of absolute 3{D} dosimetry using
                      {L}i{F} thermoluminescence detectors and polymer gels on a
                      0.35{T} {MR}-{LINAC}.},
      journal      = {Physics in medicine and biology},
      volume       = {65},
      number       = {21},
      issn         = {1361-6560},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2020-02301},
      pages        = {215002},
      year         = {2020},
      note         = {#EA:E040#LA:E040#},
      abstract     = {As shown in our previous study, highly accurate absolute
                      dosimetry in 3D is feasible by combining polymer gels (PG)
                      with thermoluminescence dosimetry (TLD). In this setup, the
                      thermoluminescence (TL)-based point dose information is used
                      to renormalize the PG. This new PG-TLD reference system is
                      now extended to measurements in magnetic fields.Experiments
                      were carried out on a conventional 6 MV linear accelerator
                      (LINAC) and a 6 MV 0.35 T magnetic resonance (MR)-LINAC.
                      Signal stability of TLD600 and TLD700 was examined without
                      and with magnetic field. Afterwards, the combination of
                      PAGAT PG and TL detectors was employed within a cylindrical
                      phantom in presence of the magnetic field. Two scenarios
                      were tested: (I) an air-filled phantom and (II) a
                      water-filled phantom. For each scenario, two plans were
                      irradiated: (a) opposed beams with a field size of 10 × 10
                      cm2 and (b) a 3D conformal plan assuring homogeneous target
                      coverage using three equally distributed coplanar beams.Mean
                      relative uncertainty of TL calibration reproducibility for
                      TLD600/TLD700 was $0.49\%/0.85\%$ at the MR-LINAC and
                      $0.48\%/0.83\%$ for the conventional LINAC. Individual TL
                      calibration coefficients of TLD600 and TLD700 behaved
                      differently in the presence of the magnetic field. An
                      average difference of (3.29 ± $0.89)\%$ occurred for all
                      TLD600, whereas the result for TLD700 is not quite as clear
                      with (1.09 ± $0.89)\%$ after excluding some outliers. Using
                      the TL dose information for PG renormalization, high 3D
                      gamma passing rates were achieved using the $3\%/2$ mm
                      criteria: $91.0\%$ (Ia), $92.6\%$ (Ib), $94.3\%$ (IIa),
                      $97.4\%$ (IIb).This study shows that TL signal
                      reproducibility is not affected by a low magnetic field.
                      Nevertheless, absolute calibration coefficients of the
                      individual detectors indicate a dependency on the magnetic
                      field. Hence, a calibration at the appropriate LINAC type is
                      recommended. Furthermore, the previously established
                      renormalization method for PG was applied to measurements at
                      a MR-LINAC and was verified as suitable for evaluations of
                      homogeneous dose distribution in the target volume.},
      cin          = {E040},
      ddc          = {530},
      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:33104524},
      doi          = {10.1088/1361-6560/aba6d7},
      url          = {https://inrepo02.dkfz.de/record/164172},
}