title: MCNP5 evaluation of dose dissipation in tissue-like media exposed to low-energy monoenergetic X-ray microbeam.
abstract: Following a significant increase in the number of facilities in the world having and developing low- and high-linear energy transfer (LET) microbeams for experimental radiobiological studies, it is useful and demanding to establish reliable computational models to analyze such experiments. This paper summarizes initial MCNP5 calculations of the basic parameters needed to study X-ray microbeam penetration, dose deposition and dose spatial dissipation in tissue-like media of micro and macro scales. The presented models can be used to predict doses delivered to neighboring cells and analyze the cause of bystander cell deaths. In the case of low-LET radiation, dose distribution is more homogenized when compared to high-LET that deposits almost all of its energy in the cell hit by radiation. Results are presented for a microbeam of monoenergetic soft (2-10 keV) X-rays for two different micro-models: (a) single-cells of homogeneous and uniform chemical compositions, and (b) single-cells of heterogeneous structures (nucleus and cytoplasm) with different chemical compositions. In both numerical models, only one cell is irradiated and the electron and X-ray doses in all cells are recorded. It was found that surrounding cells receive approximately five orders of magnitude less dose than the target cell in the homogenized cell model. The more detailed, heterogeneous model showed that the nucleus of the target cell receives more than 95% of the dose delivered to the entire cell, while neighboring cell nuclei receive approximately 65% of their total cell dose. Results of the macroscopic behavior of a soft X-ray microbeam using a cylindrical phantom 5 cm tall and 1 cm in diameter are also presented. Three-dimensional dose profiles indicate the spatial dose dissipation. For example, a 10 keV X-ray microbeam dose scatters to a negligible level at 0.3 cm radially from the center while it reaches an axial depth of 2 cm.
authors.affiliation: School of Nuclear Engineering, Purdue University, 400 Central Drive, West Lafayette, IN 47907, USA.
authors.forename: Shaun D
authors.initials: SD
authors.lastname: Clarke
authors.forename: Tatjana
authors.initials: T
authors.lastname: Jevremovic
mesh_terms: D000465:Algorithms; D001822:Body Burden; D003198:Computer Simulation; D003238:Connective Tissue / Q000502:physiology* / Q000528:radiation effects; D018499:Linear Energy Transfer / Q000502:physiology; D008954:Models, Biological; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D012062:Relative Biological Effectiveness; D012542:Scattering, Radiation; D012984:Software; D014965:X-Rays