Title page for ETD etd-11102008-093334

Type of Document Master's Thesis
Author Welch, Christopher Erik
URN etd-11102008-093334
Title Computed Tomography Imaging to Quantify Iodine Distribution in Iododeoxyuridine- Labeled DNA
Degree Master of Science (M.S.)
Department Physics & Astronomy
Advisory Committee
Advisor Name Title
Kenneth L. Matthews II Committee Chair
Brad Schaefer Committee Member
Kenneth R. Hogstrom Committee Member
Marie E. Varnes Committee Member
Polad M. Shikhaliev Committee Member
  • CHO
  • Chinese hamster ovary cells
  • IUdR
  • KES
  • Iodine
  • Iododeoxyuridine
  • microCT
  • K-edge Subtraction
  • Synchrotron
  • CT
  • Computed Tomography
Date of Defense 2008-10-28
Availability unrestricted
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 0.210.04 mg/ml using the HU calibration curve and 0.200.01 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.

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