Radiation track, DNA damage and response-a review.

The purpose of this paper has been to review the current status and progress of the field of radiation biophysics, and draw attention to the fact that physics, in general, and radiation physics in particular, with the aid of mathematical modeling, can help elucidate biological mechanisms and cancer therapies. We hypothesize that concepts of condensed-matter physics along with the new genomic knowledge and technologies and mechanistic mathematical modeling in conjunction with advances in experimental DNA (Deoxyrinonucleic acid molecule) repair and cell signaling have now provided us with unprecedented opportunities in radiation biophysics to address problems in targeted cancer therapy, and genetic risk estimation in humans. Obviously, one is not dealing with 'low-hanging fruit', but it will be a major scientific achievement if it becomes possible to state, in another decade or so, that we can link mechanistically the stages between the initial radiation-induced DNA damage; in particular, at doses of radiation less than 2 Gy and with structural changes in genomic DNA as a precursor to cell inactivation and/or mutations leading to genetic diseases. The paper presents recent development in the physics of radiation track structure contained in the computer code system KURBUC, in particular for low-energy electrons in the condensed phase of water for which we provide a comprehensive discussion of the dielectric response function approach. The state-of-the-art in the simulation of proton and carbon ion tracks in the Bragg peak region is also presented. The paper presents a critical discussion of the models used for elastic scattering, and the validity of the trajectory approach in low-electron transport. Brief discussions of mechanistic and quantitative aspects of microdosimetry, DNA damage and DNA repair are also included as developed by the authors' work.

Monte Carlo simulation of X-ray spectra and evaluation of filter effect using MCNP4C and FLUKA code.

The general-purpose MCNP4C and FLUKA codes were used for simulating X-ray spectra. The electrons were transported until they slow down and stop in the target. Both bremsstrahlung and characteristic X-ray production were considered in this work. Tungsten/aluminum combination was used as target/filter in the simulation. The results of two codes were generated in 80, 100, 120 and 140 kV and compared with each other. In order to survey filter effect on X-ray spectra, the attenuation coefficient of filter was calculated in 120 kV. More details of filter effect have been investigated. The results of MCNP4C and FLUKA are comparable in the range of bremsstrahlung spectra, but there are some differences between them especially in specific X-ray peaks. Since the specific peaks have not significant role on image quality, both FLUKA and MCNP4C codes are fairly appropriate for production of X-ray spectra and evaluating image quality, absorbed dose and improvement in filter design.