Graduate Thesis Or Dissertation
 

Predicting dose and cell survival distributions for brachytherapy sources

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qr46r290v

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  • The focus of this thesis is to determine the biological impact of dose from brachytherapy sources commonly used in cancer treatment. To achieve this goal, the Monte Carlo code PENELOPE was used to simulate point sources of four different isotopes (¹⁰³Pd, ¹²⁵I, ¹³⁷Cs, and ⁹⁰Sr) in an infinite medium of water. These dose distributions were then post processed, using the linear quadratic equation, to calculate cell survivability distributions and to produce 3D maps of arrays of identical sources. Parametric studies performed with a simple shielding model showed several important trends in the data: as particle emission intensity increases killing radius (defined as the radius from the source at which only 10⋅⁹ of the cells will survive) increases, as the shielding attenuation factor increases kill radius decreases, as the linear lesion coefficient (α) increases the kill radius increases, as the quadratic lesion coefficient (β) increases the kill radius increases weakly, as the isotopic decay constant increases the kill radius decreases, and as the rate of DNA damage repair increases the kill radius decreases weakly. Monte Carlo simulations of isotropic point sources showed that the difference between the kill radius and survival radius (defined as the distance from the source at which 10⋅⁷ of the cells survive) was smaller relative to the survival radius, for electron emitting isotopes than for photon emitting isotopes. This has been attributed to the fact that uncharged photons interact with matter through collisions, whereas, charged electrons interact through matter through collisions and Coulomb interactions. Coulomb interactions cause a continuous slowing down of the electrons, decreasing their range.
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