The Study On Track Structure In Microdosimetry And Models Of Human Normal Individual Cells

Understanding the biological effects of low doses of ionising radiation is one of the challenges of today's radiobiology research.Microdosimetry provides a quantitative description of the randomness of radiation energy deposition in small volumes.Studying the track structure of particles in a micro volume is the basis of microdosimetry.Monte Carlo simulation method can be used to simulate the interaction between particles and substances,and to quantitatively evaluate tracks.Especially in the case that it is difficult to obtain data,it is often used as a standard method to obtain values.It is shown that cells are the basic functional unit of organisms,and DNA is the most sensitive target for radiation damage in cells.Different Monte Carlo physical models concern different target sizes,so different physical models should be selected when simulating different objects.Therefore,it is necessary to study cells and DNA separately.Tracks of low-energy electrons in liquid water was analyzed and evaluated based on the Geant4-DNA toolkit of Geant4 version 10.4.According to the characteristics of different models,five physics constructors of Geant4-DNA toolkit were selected to simulate monoenergetic electrons in microscopic scale.Details of track structure of different Geant4-DNA physics constructors were compared,including total number of interaction processes,number and energy percentage of excitation and ionization;analyzing the impacts of mean lineal energy of several factors,including Geant4-DNA physics constructors,initial energy,radius of scoring spheres,interaction processes and cut-off energy.Several alternative discrete physics constructors of Geant4-DNA are comprehensively discussed overlaying multiple perspectives under different conditions in this work,it would be of basic guiding significance to help users select the appropriate model to simulate low energy monoenergetic electrons according to their needs,and provide a powerful basis for further establishing the monoenergetic electronic database to evaluate the biological effects of ionizing radiation in microscopic scale.This work proposed two voxel model of human normal individual cells,and the Monte Carlo simulation of the GATE was used to describe and analyze the effects of some factors on the microdosimetric indicator--specific energy,such as shape,volume and physical models for interaction.In this paper,Livermore and Penelope were selected to estimate the specific energy and its distribution of a lung epithelial cell(BEAS-2B)and a renal epithelial cell(293T)and their size-like simple ellipsoids(hereinafter referred to as "simple geometry")respectively,which are two of low energy electromagnetic models in GATE.Monoenergetic electrons with initial energy ranging from 50 keV to 1 MeV were selected as the "source".According to the common irradiation methods in the radiobiological cell experiments,we evaluated three specific irradiation conditions:the source isotropically irradiated within the cell,the source irradiated axially outside the cell(x-axis positive and z-axis negative)and the cell surface is covered with a polypropylene film for external irradiation.These results demonstrate that it is necessary to establish voxel phantoms of human normal individual cells for further exploring the mechanism of biological effects of radiation.At the same time,it is of great significance to construct a database of microdosimetry(e.g.energy and its mean)based on these voxel phantoms for clinical radiation protection and radiotherapy.