title: A 3-dimensional absorbed dose calculation method based on quantitative SPECT for radionuclide therapy: evaluation for (131)I using monte carlo simulation.
abstract: A general method is presented for patient-specific 3-dimensional absorbed dose calculations based on quantitative SPECT activity measurements.
  
  
  METHODS
  The computational scheme includes a method for registration of the CT image to the SPECT image and position-dependent compensation for attenuation, scatter, and collimator detector response performed as part of an iterative reconstruction method. A method for conversion of the measured activity distribution to a 3-dimensional absorbed dose distribution, based on the EGS4 (electron-gamma shower, version 4) Monte Carlo code, is also included. The accuracy of the activity quantification and the absorbed dose calculation is evaluated on the basis of realistic Monte Carlo-simulated SPECT data, using the SIMIND (simulation of imaging nuclear detectors) program and a voxel-based computer phantom. CT images are obtained from the computer phantom, and realistic patient movements are added relative to the SPECT image. The SPECT-based activity concentration and absorbed dose distributions are compared with the true ones.
  
  
  RESULTS
  Correction could be made for object scatter, photon attenuation, and scatter penetration in the collimator. However, inaccuracies were imposed by the limited spatial resolution of the SPECT system, for which the collimator response correction did not fully compensate.
  
  
  CONCLUSIONS
  The presented method includes compensation for most parameters degrading the quantitative image information. The compensation methods are based on physical models and therefore are generally applicable to other radionuclides. The proposed evaluation methodology may be used as a basis for future intercomparison of different methods.
authors.affiliation: Department of Radiation Physics, Jubileum Institute, Lund University, Sweden. Michael.ljungberg@radfys.lu.se
authors.forename: Michael
authors.initials: M
authors.lastname: Ljungberg
authors.forename: Katarina
authors.initials: K
authors.lastname: Sjögreen
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Liu
authors.forename: Eric
authors.initials: E
authors.lastname: Frey
authors.forename: Yuni
authors.initials: Y
authors.lastname: Dewaraja
authors.forename: Sven-Erik
authors.initials: SE
authors.lastname: Strand
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D007457:Iodine Radioisotopes