Identifier

etd-11102008-093334

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

Abstract

Purpose: Treatment planning for x-ray activated Auger electron radiotherapy requires knowledge of the spatial distribution of Auger electron-producing target atoms in DNA; iodine is a candidate atom. Because planning uses computed tomography (CT) data to show anatomy, obtaining the target atoms' distribution with CT methods is an attractive goal. This study evaluates the ability of two available CT systems to measure the target atoms' spatial distribution. Method and Materials: A polychromatic desktop CT scanner and a synchrotron monochromatic CT system acquired images of iodine concentrations in water, ranging from 0.03-10 mg/ml. The polychromatic scanner was operated at 40 kVp while the synchrotron system was operated at 32.5 keV and 33.5 keV. Calibration curves of Hounsfield units (HU) vs. iodine concentration were obtained from each CT set, with minimum detectable iodine concentration defined as the smallest concentration distinguishable from water with contrast-to-noise ratio of 3. K-edge subtraction (KES) analysis was applied to the synchrotron CT data as another quantification method. To determine if iodine uptake could be quantified in vitro, Chinese hamster ovary (CHO) cells grown with iododeoxyuridine (IUdR) were imaged with the synchrotron. Iodine uptake was measured with the HU calibration curve and KES. Results: The expected iodine concentration for breast cancer in vivo is estimated to be 0.06 mg/ml for IUdR. The minimum detectable iodine concentration was 0.1 mg/ml for the 40 kVp polychromatic CT data and 0.1 mg/ml for the synchrotron CT at 33.5 keV; minimum detectability using KES was 0.25 mg/ml. Thus, these current systems could not visualize the estimated target concentration. The measured iodine concentration in the cells was 0.21±0.04 mg/ml using the HU calibration curve and 0.20±0.01 mg/ml using KES, compared to an expected concentration in DNA of 0.001 mg/ml. Conclusions: Using the current acquisition methods, these CT systems proved unable to measure the expected concentration. Improvements may be possible by modifying the acquisition parameters. From the cell image results, CT imaging for treatment planning will quantify both DNA-incorporated iodine and intracellular unincorporated iodine; if the two amounts can be shown to have a stable proportion; CT quantification methods may be satisfactory for treatment planning.

Date

2008

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Kenneth L. Matthews II

DOI

10.31390/gradschool_theses.1948

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