title: Autoradiographic studies of rhenium-188-hydroxyethylidine diphosphonate in normal skeleton and osteoblastic bone metastases in a rat model of metastatic prostate cancer.
abstract: OBJECTIVE
  The quantitative distribution of bone-seeking radiopharmaceuticals in trabecular bone, cortical bone and in skeletal metastases is required for calculation of radiation-absorbed dose in radionuclide therapy. An animal model of intraosseous tumor cell administration was developed to simulate osteoblastic metastases for autoradiographic study of radionuclide localization.
  
  
  METHODS
  In 45 Copenhagen rats R3327-MATLyLu syngeneic prostate cancer cells were given intraosseously in both the femori. Rhenium-188-hydroxyethylidine diphosphonate (HEDP) was administered intravenously 17+/-1 days after cells instillation and these animals were euthanized at 4, 24 and 48 h after injection of the radiopharmaceutical. The uptake of radiopharmaceutical was estimated in normal skeleton and the bone metastases by means of region of interest analysis using autoradiography. The tumor to nontumor ratio and the fractional uptake in cortical bone and trabecular bone were quantified.
  
  
  RESULTS
  The uptake of rhenium-188-HEDP in cortical bone was 33.5% and in trabecular bones was 66.5% after 4 h, 34.6 and 65.4% after 24 h, and 35.9 and 64.1% after 48 h, respectively. Assuming a theoretic cortical-trabecular distribution of 50-50%, (MIRDOSE) calculation, radiation-absorbed dose to bone marrow was underestimated by 26%. In bone metastases, an inhomogeneous distribution with a minimal and maximal tumor to nontumor ratio of 3 : 1 and 14 : 1 after 4 h, 5 : 1 and 14 : 1 after 24 h, and 5 : 1 and 16 : 1 after 48 h was observed.
  
  
  CONCLUSIONS
  The MIRDOSE model underestimates the radiation-absorbed dose to the bone marrow because of demonstrable differences in the uptake of rhenium-188-HEDP in cortical and trabecular bone and inhomogeneous uptake in skeletal metastases.
authors.affiliation: Department of Nuclear Medicine, University Hospital Dresden, Dresden, Germany. knut.liepe@klinikum-kassel.de
authors.forename: Knut
authors.initials: K
authors.lastname: Liepe
authors.forename: Hans Heiner
authors.initials: HH
authors.lastname: Geidel
authors.forename: Ralf
authors.initials: R
authors.lastname: Bergmann
authors.forename: Michael
authors.initials: M
authors.lastname: Haase
authors.forename: Roswitha
authors.initials: R
authors.lastname: Runge
authors.forename: Joerg
authors.initials: J
authors.lastname: Kotzerke
mesh_terms: D000818:Animals; D001345:Autoradiography; D001859:Bone Neoplasms / Q000378:metabolism* / Q000556:secondary*; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D012968:Etidronic Acid / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D008159:Lumbar Vertebrae / Q000378:metabolism; D008297:Male; D010006:Osteoblasts / Q000378:metabolism* / Q000473:pathology; D011471:Prostatic Neoplasms / Q000473:pathology*; D011868:Radioisotopes; D051381:Rats; D012211:Rhenium / Q000737:chemistry*; D014018:Tissue Distribution
chemical_list: D011868:Radioisotopes; D012211:Rhenium; D012968:Etidronic Acid