title: Cellular- and micro-dosimetry of heterogeneously distributed tritium.
abstract: OBJECTIVE
  The assessment of radiotoxicity for heterogeneously distributed tritium should be based on the subcellular dose and relative biological effectiveness (RBE) for cell nucleus. In the present work, geometry-dependent absorbed dose and RBE were calculated using Monte Carlo codes for tritium in the cell, cell surface, cytoplasm, or cell nucleus.
  
  
  METHODS
  Penelope (PENetration and Energy LOss of Positrins and Electrons) code was used to calculate the geometry-dependent absorbed dose, lineal energy, and electron fluence spectrum. RBE for the intestinal crypt regeneration was calculated using a lineal energy-dependent biological weighting function. RBE for the induction of DNA double strand breaks was estimated using a nucleotide-level map for clustered DNA lesions of the Monte Carlo damage simulation (MCDS) code.
  
  
  RESULTS
  For a typical cell of 10 μm radius and 5 μm nuclear radius, tritium in the cell nucleus resulted in much higher RBE-weighted absorbed dose than tritium distributed uniformly. Conversely, tritium distributed on the cell surface led to trivial RBE-weighted absorbed dose due to irradiation geometry and great attenuation of beta particles in the cytoplasm. For tritium uniformly distributed in the cell, the RBE-weighted absorbed dose was larger compared to tritium uniformly distributed in the tissue.
  
  
  CONCLUSIONS
  Cellular- and micro-dosimetry models were developed for the assessment of heterogeneously distributed tritium.
authors.affiliation: Department of Medical Imaging and Radiological Sciences, Chang Gung University, Taoyuan, Taipei, Taiwan.
authors.forename: Tsi-Chian
authors.initials: TC
authors.lastname: Chao
authors.forename: Chun-Ching
authors.initials: CC
authors.lastname: Wang
authors.forename: Junli
authors.initials: J
authors.lastname: Li
authors.forename: Chunyan
authors.initials: C
authors.lastname: Li
authors.forename: Chuan-Jong
authors.initials: CJ
authors.lastname: Tung
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects; D003593:Cytoplasm / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology* / Q000378:metabolism* / Q000528:radiation effects; D055616:Microtechnology / Q000379:methods*; D009010:Monte Carlo Method; D011874:Radiometry; D012062:Relative Biological Effectiveness; D014316:Tritium / Q000009:adverse effects / Q000378:metabolism*
chemical_list: D014316:Tritium