title: Track structure, radiation quality and initial radiobiological events: considerations based on the PARTRAC code experience.
abstract: OBJECTIVE
  The role of track structures for understanding the biological effects of radiation has been the subject of research activities for decades. The physics that describes such processes is the core Monte Carlo codes, such as the biophysical PARTRAC (PARticle TRACks) code described in this review, which follow the mechanisms of radiation-matter interaction from the early stage. In this paper a review of the track structure theory (and of its possible extension concerning non-DNA targets) is presented.
  
  
  METHODS
  The role of radiation quality and track structure is analyzed starting from the heavy ions results obtained with the biophysical Monte Carlo code PARTRAC (PARticles TRACks). PARTRAC calculates DNA damage in human cells based on the superposition of simulated track structures in liquid water to an 'atom-by-atom' model of human DNA.
  
  
  RESULTS
  Calculations for DNA fragmentation compared with experimental data for different radiation qualities are illustrated. As an example, the strong dependence of the complexity of DNA damage on radiation track structure, and the very large production of very small DNA fragments (lower than 1 kbp (kilo base pairs) usually not detected experimentally) after high LET (high-Linear Energy Transfer) irradiation is shown. Furthermore the possible importance of non-nuclear/non-DNA targets is discussed in the particular case of cellular membrane and mitochondria.
  
  
  CONCLUSIONS
  The importance of the track structure is underlined, in particular the dependence of a given late cellular effect on the spatial distribution of DNA double-strand breaks (DSB) along the radiation track. These results show that the relative biological effectiveness (RBE) for DSB production can be significantly larger than 1. Moreover the cluster properties of high LET radiation may determine specific initial targets and damage evolution.
authors.affiliation: Laboratorio Energia Nucleare Applicata, Università degli studi di Pavia, Pavia, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Alloni
authors.forename: Alessandro
authors.initials: A
authors.lastname: Campa
authors.forename: Werner
authors.initials: W
authors.lastname: Friedland
authors.forename: Luca
authors.initials: L
authors.lastname: Mariotti
authors.forename: Andrea
authors.initials: A
authors.lastname: Ottolenghi
mesh_terms: D000512:Alpha Particles / Q000009:adverse effects; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D053904:DNA Breaks, Single-Stranded / Q000528:radiation effects; D004583:Electrons / Q000009:adverse effects; D006801:Humans; D009010:Monte Carlo Method; D017785:Photons / Q000009:adverse effects; D011853:Radiobiology / Q000379:methods*