title: Use of Monte Carlo simulations with a realistic rat phantom for examining the correlation between hematopoietic system response and red marrow absorbed dose in Brown Norway rats undergoing radionuclide therapy with (177)Lu- and (90)Y-BR96 mAbs.
abstract: OBJECTIVE
  Biokinetic and dosimetry studies in laboratory animals often precede clinical radionuclide therapies in humans. A reliable evaluation of therapeutic efficacy is essential and should be based on accurate dosimetry data from a realistic dosimetry model. The aim of this study was to develop an anatomically realistic dosimetry model for Brown Norway rats to calculate S factors for use in evaluating correlations between absorbed dose and biological effects in a preclinical therapy study.
  
  
  METHODS
  A realistic rat phantom (Roby) was used, which has some flexibility that allows for a redefinition of organ sizes. The phantom was modified to represent the anatomic geometry of a Brown Norway rat, which was used for Monte Carlo calculations of S factors. Kinetic data for radiolabeled BR96 monoclonal antibodies were used to calculate the absorbed dose. Biological data were gathered from an activity escalation study with (90)Y- and (177)Lu-labeled BR96 monoclonal antibodies, in which blood cell counts and bodyweight were examined up to 2 months follow-up after injection. Reductions in white blood cell and platelet counts and declines in bodyweight were quantified by four methods and compared to the calculated absorbed dose to the bone marrow or the total body.
  
  
  RESULTS
  A red marrow absorbed dose-dependent effect on hematological parameters was observed, which could be evaluated by a decrease in blood cell counts. The absorbed dose to the bone marrow, corresponding to the maximal tolerable activity that could safely be administered, was determined to 8.3 Gy for (177)Lu and 12.5 Gy for (90)Y.
  
  
  CONCLUSIONS
  There was a clear correlation between the hematological effects, quantified with some of the studied parameters, and the calculated red marrow absorbed doses. The decline in body weight was stronger correlated to the total body absorbed dose, rather than the red marrow absorbed dose. Finally, when considering a constant activity concentration, the phantom weight, ranging from 225 g to 300 g, appeared to have no substantial effect for the estimated absorbed dose.
authors: Department of Medical Radiation Physics, Clinical Sciences, Lund University, Lund, Sweden. erik.larsson@med.lu.se
authors: Erik
authors: E
authors: Larsson
authors: Michael
authors: M
authors: Ljungberg
authors: Linda
authors: L
authors: Martensson
authors: Rune
authors: R
authors: Nilsson
authors: Jan
authors: J
authors: Tennvall
authors: Sven-Erik
authors: SE
authors: Strand
authors: Bo-Anders
authors: BA
authors: Jonsson
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics*; D040761:Biomimetic Materials; D001853:Bone Marrow / Q000378:metabolism* / Q000528:radiation effects*; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D006413:Hematopoietic System / Q000378:metabolism* / Q000528:radiation effects*; D008187:Lutetium / Q000493:pharmacokinetics*; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011868:Radioisotopes / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D013223:Statistics as Topic; D015021:Yttrium Radioisotopes / Q000493:pharmacokinetics
chemical_list: D000911:Antibodies, Monoclonal; C507851:BR96 monoclonal antibody; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D015021:Yttrium Radioisotopes; D008187:Lutetium