WE‐C‐332‐04: Computed Tomography Imaging to Quantify Iodine Distribution in IUdR‐Labeled DNA

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Conference Proceeding

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Purpose: Treatment planning for X‐ray Activated Auger electron radiotherapy requires CT data sets correlated to the distribution of preloaded high Z radiosensitizer molecules in cellular DNA. The study's aim was to evaluate a polychromatic microCT scanner and a synchrotron monochromatic CT system for their ability to measure the spatial distribution of iodine incorporated in DNA. Method and Materials: The Skyscan 1074 microCT system produces images at 20–40 kVp with a 736×512 element CCD camera. CT images were acquired at 40 kVp and 1000 μA. The synchrotron produces a tunable (6–35 keV) monochromatic beam with a beam profile of 0.1×2.8 cm2 and a 1.5k×1k CCD camera with focusing lenses to obtain CT images with pixel sizes of 4.5–9.0 μm. CT images were acquired above (33.8 keV) and below (32.5 keV) iodine's K‐edge binding energy of 33.169 keV. Phantoms were constructed from acrylic for the benchtop microCT system or glass micro‐hematocrit capillary tubes for the synchrotron based monochromatic CT system. Iodine contrast agent (Reno‐30) was diluted with distilled‐deionized water in concentrations 0.05–25 mg I ml−1. Results: Results from the microCT system and the synchrotron K‐edge subtraction data were fit using linear regression. The fit parameters for the Skyscan and CAMD (33.8 keV) data were CT♯ =2.39 + 29.7×[I] with χν2=0.282 and CT♯ =6.80 + 82.74×[I] with χν2=1.37 respectively. The fit parameters for the K‐edge subtraction were [I]meas= − 0.00968 + 0.677×[I]known with χν2=1.61. Conclusion: Noise limited the microCT's accuracy at low iodine concentrations. K‐edge subtraction using monochromatic x‐rays is promising but the glass capillary tubes have proved too attenuating for test measurements. Measurement of 0.06 mg I ml−1 (corresponding to 18% thymidine replacement) appeared feasible. The imaging methods are being applied to studying Chinese hamster ovary cells containing iododeoxyuridine‐labeled DNA to verify the magnitude and distribution of iodine incorporation in cell samples. © 2008, American Association of Physicists in Medicine. All rights reserved.

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Medical Physics

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