title: Biologic dosimetry of bone marrow: induction of micronuclei in reticulocytes after exposure to 32P and 90Y.
abstract: Bone marrow is the dose-limiting organ in targeted radionuclide therapy. Hence, determination of the absorbed dose to bone marrow from incorporated radionuclides is a critical element in treatment planning. This study investigated the potential of the micronucleus assay in peripheral blood reticulocytes (MnRETs) as an in vivo biologic dosimeter for bone marrow.
  
  
  METHODS
  After intravenous administration of 32P-orthophosphate or 90Y-citrate in Swiss Webster mice, DNA damage induced in bone marrow erythroblastoid cells was measured by subsequent scoring of MnRETs in peripheral blood. The response to exponentially decreasing dose rates was calibrated by irradiating animals with external 137Cs-gamma-rays. The gamma-ray dose rate was decreased exponentially, with the dose-rate decrease half-time corresponding to the effective clearance half-time (Te) of the radioactivity from the femoral bone (Te = 64 h for 90Y-citrate and Te = 255 h for 32P-orthophosphate).
  
  
  RESULTS
  The maximum MnRETs frequency occurred on the second and third day after injection of 90Y-citrate and 32P-orthophosphate, respectively. The same pattern was observed for exponentially decreasing dose rates of 137Cs-gamma-rays. For each type of exposure, the maximum MnRETs frequency increased in a dose-dependent manner. Using the calibrated dosimeter, the initial dose rates to the marrow per unit of injected activity were 0.0020 cGy/h/kBq and 0.0026 cGy/h/kBq for 32P-orthophosphate and 90Y-citrate, respectively.
  
  
  CONCLUSIONS
  Micronuclei in peripheral blood reticulocytes can be used as a noninvasive biologic dosimeter for measuring absorbed dose rate and absorbed dose to bone marrow from incorporated radionuclides.
authors.affiliation: Department of Radiology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark 07103, USA.
authors.forename: M
authors.initials: M
authors.lastname: Lenarczyk
authors.forename: S M
authors.initials: SM
authors.lastname: Goddu
authors.forename: D V
authors.initials: DV
authors.lastname: Rao
authors.forename: R W
authors.initials: RW
authors.lastname: Howell
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D051379:Mice; D048629:Micronuclei, Chromosome-Defective / Q000648:ultrastructure*; D010761:Phosphorus Radioisotopes; D011874:Radiometry / Q000379:methods; D012156:Reticulocytes / Q000528:radiation effects* / Q000648:ultrastructure; D015021:Yttrium Radioisotopes
chemical_list: D010761:Phosphorus Radioisotopes; D015021:Yttrium Radioisotopes