title: Evaluating the Application of Tissue-Specific Dose Kernels Instead of Water Dose Kernels in Internal Dosimetry: A Monte Carlo Study.
abstract: OBJECTIVE
  The aim of this work is to evaluate the application of tissue-specific dose kernels instead of water dose kernels to improve the accuracy of patient-specific dosimetry by taking tissue heterogeneities into consideration.
  
  
  METHODS
  Tissue-specific dose point kernels (DPKs) and dose voxel kernels (DVKs) for yttrium-90 (90Y), lutetium-177 (177Lu), and phosphorus-32 (32P) are calculated using the Monte Carlo (MC) simulation code GATE (version 7). The calculated DPKs for bone, lung, adipose, breast, heart, intestine, kidney, liver, and spleen are compared with those of water. The dose distribution in normal and tumorous tissues in lung, liver, and bone of a Zubal phantom is calculated using tissue-specific DVKs instead of those of water in conventional methods. For a tumor defined in a heterogeneous region in the Zubal phantom, the absorbed dose is calculated using a proposed algorithm, taking tissue heterogeneity into account. The algorithm is validated against full MC simulations.
  
  
  RESULTS
  The simulation results indicate that the highest differences between water and other tissue DPKs occur in bone for90Y (12.2% ± 0.6%),32P (18.8% ± 1.3%), and177Lu (16.9% ± 1.3%). The second highest discrepancy corresponds to the lung for90Y (6.3% ± 0.2%),32P (8.9% ± 0.4%), and177Lu (7.7% ± 0.3%). For90Y, the mean absorbed dose in tumorous and normal tissues is calculated using tissue-specific DVKs in lung, liver, and bone. The results are compared with doses calculated considering the Zubal phantom water equivalent and the relative differences are 4.50%, 0.73%, and 12.23%, respectively. For the tumor in the heterogeneous region of the Zubal phantom that includes lung, liver, and bone, the relative difference between mean calculated dose in tumorous and normal tissues based on the proposed algorithm and the values obtained from full MC dosimetry is 5.18%.
  
  
  CONCLUSIONS
  A novel technique is proposed considering tissue-specific dose kernels in the dose calculation algorithm. This algorithm potentially enables patient-specific dosimetry and improves estimation of the average absorbed dose of90Y in a tumor located in lung, bone, and soft tissue interface by 6.98% compared with the conventional methods.
authors.affiliation: 1 Department of Radiation Medicine Engineering, Shahid Beheshti University , Tehran, Iran .
authors.forename: Maryam
authors.initials: M
authors.lastname: Khazaee Moghadam
authors.affiliation: 1 Department of Radiation Medicine Engineering, Shahid Beheshti University , Tehran, Iran .
authors.forename: Alireza
authors.initials: A
authors.lastname: Kamali Asl
authors.affiliation: 2 Research Center for Nuclear Medicine, Shariati Hospital, Tehran University of Medical Sciences , Tehran, Iran .
authors.forename: Parham
authors.initials: P
authors.lastname: Geramifar
authors.affiliation: 3 Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital , Geneva, Switzerland .|4 Geneva Neuroscience Center, Geneva University , Geneva, Switzerland .|5 Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen , Groningen, The Netherlands .
authors.forename: Habib
authors.initials: H
authors.lastname: Zaidi
mesh_terms: D000465:Algorithms; D001859:Bone Neoplasms / Q000737:chemistry / Q000000981:diagnostic imaging / Q000378:metabolism; D003198:Computer Simulation; D006801:Humans; D008113:Liver Neoplasms / Q000737:chemistry / Q000000981:diagnostic imaging / Q000378:metabolism; D008175:Lung Neoplasms / Q000737:chemistry / Q000000981:diagnostic imaging / Q000378:metabolism; D008187:Lutetium / Q000737:chemistry / Q000493:pharmacokinetics; D009010:Monte Carlo Method; D009928:Organ Specificity; D010761:Phosphorus Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics; D011868:Radioisotopes / Q000737:chemistry* / Q000493:pharmacokinetics; D011874:Radiometry / Q000379:methods*; D011877:Radionuclide Imaging / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D014867:Water / Q000737:chemistry*; D015021:Yttrium Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics
chemical_list: D010761:Phosphorus Radioisotopes; D011868:Radioisotopes; D015021:Yttrium Radioisotopes; D014867:Water; D008187:Lutetium
keywords: Monte Carlo simulation; dose point kernel; patient-specific dosimetry; tissue heterogeneity