title: Evaluation of S-values and dose distributions for (90)Y, (131)I, (166)Ho, and (188)Re in seven lobes of the rat liver.
abstract: OBJECTIVE
  Rats have been widely used in radionuclide therapy research for the treatment of hepatocellular carcinoma (HCC). This has created the need to assess rat liver absorbed radiation dose. In most dose estimation studies, the rat liver is considered as a homogeneous integrated target organ with a tissue composition assumed to be similar to that of human liver tissue. However, the rat liver is composed of several lobes having different anatomical and chemical characteristics. To assess the overall impact on rat liver dose calculation, the authors use a new voxel-based rat model with identified suborgan regions of the liver.
  
  
  METHODS
  The liver in the original cryosectional color images was manually segmented into seven individual lobes and subsequently integrated into a voxel-based computational rat model. Photon and electron particle transport was simulated using the MCNPX Monte Carlo code to calculate absorbed fractions and S-values for (90)Y, (131)I, (166)Ho, and (188)Re for the seven liver lobes. The effect of chemical composition on organ-specific absorbed dose was investigated by changing the chemical composition of the voxel filling liver material. Radionuclide-specific absorbed doses at the voxel level were further assessed for a small spherical hepatic tumor.
  
  
  RESULTS
  The self-absorbed dose for different liver lobes varied depending on their respective masses. A maximum difference of 3.5% was observed for the liver self-absorbed fraction between rat and human tissues for photon energies below 100 keV. (166)Ho and (188)Re produce a uniformly distributed high dose in the tumor and relatively low absorbed dose for surrounding tissues.
  
  
  CONCLUSIONS
  The authors evaluated rat liver radiation doses from various radionuclides used in HCC treatments using a realistic computational rat model. This work contributes to a better understanding of all aspects influencing radiation transport in organ-specific radiation dose evaluation for preclinical therapy studies, from tissue composition to organ morphology and activity distribution.
authors.affiliation: Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Tianwu
authors.initials: T
authors.lastname: Xie
authors.forename: Qian
authors.initials: Q
authors.lastname: Liu
authors.forename: Habib
authors.initials: H
authors.lastname: Zaidi
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000532:radiotherapy; D004583:Electrons; D006695:Holmium / Q000627:therapeutic use*; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008099:Liver / Q000528:radiation effects*; D008113:Liver Neoplasms / Q000532:radiotherapy; D009010:Monte Carlo Method; D017785:Photons / Q000627:therapeutic use; D011829:Radiation Dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D012211:Rhenium / Q000627:therapeutic use*; D015021:Yttrium Radioisotopes / Q000627:therapeutic use
chemical_list: D007457:Iodine Radioisotopes; D015021:Yttrium Radioisotopes; D012211:Rhenium; D006695:Holmium