Radiobiological modeling using track structure analysis
Coghill, Matthew Taylor
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The purpose of this thesis is to present data pertinent to and propose conclusions regarding the coordination of radiobiologic effectiveness (RBE) and linear energy transfer (LET). RBE is a quantity relating the effectiveness of different radiations in causing cell death. LET is a measure of the rate of energy transferred to material by an ionizing particle. This relationship of these values varies for different particles. The reason for this is still inconclusive. The petitioner has made use of a toolkit for Geant4, known as Geant4-DNA, to perform track-structure analysis on a chromosome model. Geant4 is an object-oriented program for the "simulation of the passage of particles through matter" developed by CERN that makes use of Monte Carlo methods and is expanded by Geant4-DNA to handle low-energy electron physics as well as physic-chemical effects. The chromosome model, in this case, has been developed by the petitioner as a nucleus with a basic, uniform distribution of chromatin. Radiation damage to DNA, in the form of aberrations, lesions and strand breaks, can be coordinated to energy deposited or number of ionizations occurring in the target (in this case DNA or chromatin fiber). Certain threshold values have been established as indicate of different types of DNA damage. The ultimate goal of this work is to score these clusters of events against the threshold values to determine the severity of DNA damage. The final comparison of the results for different particles will provide for a better understanding of the RBE-LET relationships by improving the understanding of the underlying nanodosimetric qualities.