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@ARTICLE{Hammes:20155,
      author       = {Hammes, J. and Pietrzyk, U. and Schmidt, M. and Schicha, H.
                      and Eschner, W.},
      title        = {{GATE} based {M}onte {C}arlo simulation of planar
                      scintigraphy to estimate the nodular dose in radioiodine
                      therapy for autonomous thyroid adenoma},
      journal      = {Zeitschrift für Medizinische Physik},
      volume       = {21},
      issn         = {0939-3889},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier},
      reportid     = {PreJuSER-20155},
      pages        = {290 - 300},
      year         = {2011},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {The recommended target dose in radioiodine therapy of
                      solitary hyperfunctioning thyroid nodules is 300-400Gy and
                      therefore higher than in other radiotherapies. This is due
                      to the fact that an unknown, yet significant portion of the
                      activity is stored in extranodular areas but is neglected in
                      the calculatory dosimetry. We investigate the feasibility of
                      determining the ratio of nodular and extranodular activity
                      concentrations (uptakes) from post-therapeutically acquired
                      planar scintigrams with Monte Carlo simulations in GATE. The
                      geometry of a gamma camera with a high energy collimator was
                      emulated in GATE (Version 5). A geometrical thyroid-neck
                      phantom (GP) and the ICRP reference voxel phantoms "Adult
                      Female" (AF, 16ml thyroid) and "Adult Male" (AM, 19ml
                      thyroid) were used as source regions. Nodules of 1ml and 3ml
                      volume were placed in the phantoms. For each phantom and
                      each nodule 200 scintigraphic acquisitions were simulated.
                      Uptake ratios of nodule and rest of thyroid ranging from 1
                      to 20 could be created by summation. Quantitative image
                      analysis was performed by investigating the number of
                      simulated counts in regions of interest (ROIs). ROIs were
                      created by perpendicular projection of the phantom onto the
                      camera plane to avoid a user dependant bias. The ratio of
                      count densities in ROIs over the nodule and over the
                      contralateral lobe, which should be least affected by
                      nodular activity, was taken to be the best available measure
                      for the uptake ratios. However, the predefined uptake ratios
                      are underestimated by these count density ratios: For an
                      uptake ratio of 20 the count ratios range from 4.5 (AF, 1ml
                      nodule) to 15.3 (AM, 3ml nodule). Furthermore, the
                      contralateral ROI is more strongly affected by nodular
                      activity than expected: For an uptake ratio of 20 between
                      nodule and rest of thyroid up to $29\%$ of total counts in
                      the ROI over the contralateral lobe are caused by decays in
                      the nodule (AF 3 ml). In the case of the 1ml nodules this
                      effect is smaller: $9-11\%$ (AF) respectively $7-8\%$ (AM).
                      For each phantom, the dependency of count density ratios
                      upon uptake ratios can be modeled well by both linear and
                      quadratic regression (quadratic: r(2)>0.99), yielding sets
                      of parameters which in reverse allow the computation of
                      uptake ratios (and thus dose) from count density ratios. A
                      single regression model obtained by fitting the data of all
                      simulations simultaneously did not provide satisfactory
                      results except for GP, while underestimating the true uptake
                      ratios in AF and overestimating them in AM. The
                      scintigraphic count density ratios depend upon the uptake
                      ratios between nodule and rest of thyroid, upon their
                      volumes, and their respective position in a non-trivial way.
                      Further investigations are required to derive a
                      comprehensive rule to calculate the uptake or dose ratios
                      based on post-therapeutic scintigraphy.},
      keywords     = {Adult / Female / Humans / Iodine Radioisotopes:
                      administration $\&$ dosage / Iodine Radioisotopes:
                      pharmacokinetics / Monte Carlo Method / Phantoms, Imaging /
                      Radiometry: methods / Radionuclide Imaging: methods /
                      Radiotherapy Planning, Computer-Assisted: methods / Thyroid
                      Gland: radiation effects / Thyroid Gland: radionuclide
                      imaging / Thyroid Neoplasms: radionuclide imaging / Thyroid
                      Neoplasms: radiotherapy / Thyroid Nodule: radionuclide
                      imaging / Thyroid Nodule: radiotherapy / Iodine
                      Radioisotopes (NLM Chemicals) / J (WoSType)},
      cin          = {INM-4},
      ddc          = {610},
      cid          = {I:(DE-Juel1)INM-4-20090406},
      pnm          = {Neurowissenschaften},
      pid          = {G:(DE-Juel1)FUEK255},
      shelfmark    = {Radiology, Nuclear Medicine $\&$ Medical Imaging},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:21983024},
      UT           = {WOS:000299444800008},
      doi          = {10.1016/j.zemedi.2011.09.002},
      url          = {https://juser.fz-juelich.de/record/20155},
}