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A revised dosimetric model for calculation of electron dose in the small intestine
Abstract
In this study, a revised model of the small intestine (SI) was developed for electron dosimetry using Monte Carlo techniques. The model values were estimated from an anatomic and histologic review of the SI. This study reveals that the biologically important and radiosensitive cell populations (stem cells) are located near the bottom of the crypts. For an average adult human male, the lumen radius and wall thickness were estimated to be 1.4 cm with range 0.95-1.55 cm and 0.3 cm with range 0.2-0.4 cm, respectively, while the distance of stem cells from the contents-mucus interface was estimated to be 845 [] 75 []m. The study showed that the relatively complex structure of the SI could be described by simple cylindrical geometry for Monte Carlo dose calculations. The model was implemented in the Monte Carlo N-Particle Transport Code (MCNP), version 4A, for the energy range 10-500 keV. Detailed physics treatment was implemented in the code to transport all secondary radiations generated from primary interactions, such as knock-on electrons and bremsstrahlungs. Electron depth dose distributions were calculated for the five geometries corresponding to the cylindrical SI with average dimensions, and with two extreme values of wall thickness and lumen radius. These depth dose curves showed that only a small fraction of the energy absorbed at the contents-mucus interface reaches stem cell layers. This fraction, as estimated in this study, was found to vary from 1.66x10⁻⁶ to 1.21x10⁻¹ over the energy range 10-500 keV. This clearly demonstrates that the use of the interface dose to represent the "wall" dose represents an overestimate of the true electron dose to the biologically important cells. The study showed that this fraction is very sensitive to the depth of the critical cells (stem cells) in the wall for the electrons having range greater than this depth. Uncertainty in the wall-thickness has practically no effect on depth doses across the SI wall for the energies studied. This study shows that the lumen radius has significant effect on the depth doses in the wall and the doses change by approximately inverse square of the lumen radius.
Description
Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves 113-117).
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Citation
Bhuiyan, Md. Nasir Uddin (2000). A revised dosimetric model for calculation of electron dose in the small intestine. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2000 -THESIS -B48.
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