Theoretical ionization and capture cross sections for DNA nucleobases impacted by light ions.

PURPOSE: Although DNA lesions are considered of prime importance for describing the post-irradiation cellular survival, they still remain rarely studied on both experimental and theoretical sides. Under these conditions, we here propose different theoretical models for predicting the single ionization and single capture total cross sections for DNA bases impacted by protons. MATERIAL AND METHODS: Three theoretical approaches are developed: a first classical one based on a classical trajectory Monte Carlo (CTMC) model and two quantum mechanical ones, namely, a Coulomb Born (CB1) and a continuum-distorted wave eikonal-initial-state (CDW-EIS) model. RESULTS: Ionization and capture processes induced by protons on DNA bases (adenine, cytosine, thymine and guanine) are here studied in terms of total cross sections. CONCLUSIONS: A very good agreement is obtained between the different models at high enough impact velocities but discrepancies are observed between them at low impact energies (E(i) ≤ 100 keV). Furthermore, it is shown that the theoretical cross sections underestimate the rare existing experimental data in particular for adenine and thymine whereas a reasonable agreement is found for cytosine.

Limitations (and merits) of PENELOPE as a track-structure code.

PURPOSE: To outline the limitations of PENELOPE (acronym of PENetration and Energy LOss of Positrons and Electrons) as a track-structure code, and to comment on modifications that enable its fruitful use in certain microdosimetry and nanodosimetry applications. METHODS: Attention is paid to the way in which inelastic collisions of electrons are modelled and to the ensuing implications for microdosimetry analysis. RESULTS: Inelastic mean free paths and collision stopping powers calculated with PENELOPE and two well-known optical-data models are compared. An ad hoc modification of PENELOPE is summarized where ionization and excitation of liquid water by electron impact is simulated using tables of realistic differential and total cross sections. CONCLUSIONS: PENELOPE can be employed advantageously in some track-structure applications provided that the default model for inelastic interactions of electrons is replaced by suitable tables of differential and total cross sections.