title: Cellular dose conversion factors for alpha-particle--emitting radionuclides of interest in radionuclide therapy.
abstract: alpha-Particle--emitting radionuclides are of increasing interest in radionuclide therapy. The decay scheme of alpha-emitting radionuclides typically includes a chain of unstable progeny. It is generally assumed that alpha-particle emission by the parent radionuclide will break the chemical bond with its carrier molecule and that the resulting daughter atom will no longer be associated with the carrier molecule. If the daughter is very short lived, it will not have enough time to be carried any significant distance from the site of parent decay and a cellular, absorbed dose estimate must consider the energy deposited by the daughter as well as the parent. Depending on the site of parent decay and the expected removal rate of daughter atoms from this site, the contribution of emissions from longer-lived daughters may also be warranted. In this study, dose conversion factors (DCFs) for cellular dimensions that incorporate the fate of daughter radionuclides were derived for (225)Ac, (213)Bi, (211)At, and (223)Ra, the alpha-particle--emitting radionuclides of interest in radionuclide therapy.
  
  
  METHODS
  The dose contribution of daughter radionuclides at the site of parent decay was made dependent on a cutoff time parameter, which was used to estimate the fraction of daughter decays expected at the site of parent decay. Previously tabulated S values (cell-surface to nucleus and cell-surface to cell) for each daughter in the decay scheme were scaled by this fraction and a sum over all daughters was performed to yield a cutoff time--dependent set of corresponding DCF values for each radionuclide.
  
  
  RESULTS
  DCF values for the absorbed dose to the nuclear or cellular volume from cell-surface decays are presented as a function of the cutoff time for 4 different cellular and nuclear dimensions.
  
  
  CONCLUSIONS
  In contrast to the cellular S values that account only for parent decay, the DCF values provided in this study make it possible to easily include the contribution of daughter decays in cellular alpha-particle emitter dose calculations.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Hamacher
authors.forename: R B
authors.initials: RB
authors.lastname: Den
authors.forename: E I
authors.initials: EI
authors.lastname: Den
authors.forename: G
authors.initials: G
authors.lastname: Sgouros
mesh_terms: D000465:Algorithms; D000512:Alpha Particles; D002477:Cells / Q000528:radiation effects*; D006801:Humans; D011868:Radioisotopes / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods*
chemical_list: D011868:Radioisotopes