title: Track structure in radiation biology: theory and applications.
abstract: OBJECTIVE
  A brief review is presented of the basic concepts in track structure and the relative merit of various theoretical approaches adopted in Monte-Carlo track-structure codes are examined. In the second part of the paper, a formal cluster analysis is introduced to calculate cluster-distance distributions.
  
  
  METHODS
  Total experimental ionization cross-sections were least-square fitted and compared with the calculation by various theoretical methods. Monte-Carlo track-structure code Kurbuc was used to examine and compare the spectrum of the secondary electrons generated by using functions given by Born-Bethe, Jain-Khare, Gryzinsky, Kim-Rudd, Mott and Vriens' theories. The cluster analysis in track structure was carried out using the k-means method and Hartigan algorithm.
  
  
  RESULTS
  Data are presented on experimental and calculated total ionization cross-sections: inverse mean free path (IMFP) as a function of electron energy used in Monte-Carlo track-structure codes; the spectrum of secondary electrons generated by different functions for 500 eV primary electrons; cluster analysis for 4 MeV and 20 MeV alpha-particles in terms of the frequency of total cluster energy to the root-mean-square (rms) radius of the cluster and differential distance distributions for a pair of clusters; and finally relative frequency distribution for energy deposited in DNA, single-strand break and double-strand breaks for 10MeV/u protons, alpha-particles and carbon ions.
  
  
  CONCLUSIONS
  There are a number of Monte-Carlo track-structure codes that have been developed independently and the bench-marking presented in this paper allows a better choice of the theoretical method adopted in a track-structure code to be made. A systematic bench-marking of cross-sections and spectra of the secondary electrons shows differences between the codes at atomic level, but such differences are not significant in biophysical modelling at the macromolecular level. Clustered-damage evaluation shows: that a substantial proportion of dose ( 30%) is deposited by low-energy electrons; the majority of DNA damage lesions are of simple type; the complexity of damage increases with increased LET, while the total yield of strand breaks remains constant; and at high LET values nearly 70% of all double-strand breaks are of complex type.
authors.affiliation: MRC, Radiation and Genome Stability Unit, Harwell, Oxfordshire, UK.
authors.forename: H
authors.initials: H
authors.lastname: Nikjoo
authors.forename: S
authors.initials: S
authors.lastname: Uehara
authors.forename: W E
authors.initials: WE
authors.lastname: Wilson
authors.forename: M
authors.initials: M
authors.lastname: Hoshi
authors.forename: D T
authors.initials: DT
authors.lastname: Goodhead
mesh_terms: D000512:Alpha Particles; D000818:Animals; D004247:DNA / Q000528:radiation effects; D004249:DNA Damage; D006801:Humans; D009010:Monte Carlo Method; D011522:Protons; D011839:Radiation, Ionizing; D011853:Radiobiology
chemical_list: D011522:Protons; D004247:DNA