Type of Document	Master's Thesis
Author	Oves, Scott
Author's Email Address	soves1@lsu.edu
URN	etd-01182008-133454
Title	Dosimetry Intercomparison Using a 35-keV X-Ray Synchrotron Beam
Degree	Master of Science (M.S.)
Department	Physics & Astronomy
Advisory Committee	Advisor Name Title Kenneth R. Hogstrom Committee Chair Erno Sajo Committee Member Joseph Dugas Committee Member Leslie Butler Committee Member Maurice King Committee Member
Keywords	radiation therapy synchrotron auger electron therapy gafchromic dosimetry monochromatic
Date of Defense	2007-11-14
Availability	unrestricted
Abstract Significance: Photon activated Auger electron therapy utilizes a keV-ranged, monoenergetic x-ray beam, and radiobiological and animal experiments studying this therapy require accurate dosimetry techniques. However, there exist few dosimetry protocols for low-energy x-ray beams. This research intended to use the CAMD synchrotron as a source of monochromatic, 35-keV x-rays and test dosimetry techniques of film and ion chamber. The hypothesis of my research was that depth-dose measured in a PMMA phantom using an air-equivalent ionization chamber and radiochromic film dosimeters in a PMMA phantom irradiated by a 35-keV, monochromatic x-ray beam will agree to within 5% of each other and to within 5% of dose determined from fluence-scaled Monte Carlo dose simulations. Methods: The narrow beam produced on the CAMD tomography beamline (0.1×2.8 cm2) was effectively broadened (2.5×2.8 cm2) by vertically oscillating experimental apparatus. Beam energy selected by the monochromator was verified using a Compton scatterer and powder diffraction methods. Depth-dose in PMMA was measured by an air-equivalent ion chamber using a modified AAPM’s TG-61 (100-300 kV) formalism and by Gafchromic EBT film using 125-kVp calibration curves. Depth-dose was also determined from scaling MCNP5 Monte Carlo output by fluence measured using a NaI detector. Results: The powder diffraction energy measurement agreed closest to the monochromator’s setting (mean = -0.1±0.3 keV). Depth-doses performed on 5 separate experimental dates showed that beam fluence did not accurately scale to synchrotron ring current between dates. Depth-dose measurements from ion chamber and film at 2 cm resulted in film-measured dose underestimating ion-chamber measured dose by an average of 5.0±2.1%. Fractional Monte Carlo depth-dose simulations agreed well with ion chamber and film measurements, with maximum disagreements of 3.9% at 9.0-cm depth and 0.9% at 8.25 cm, respectively. Fluence-scaled, Monte Carlo dose determination overestimated ion chamber-measured depth-dose by 6.4±0.8% and overestimated film-measured depth-dose by 9.1±0.7%. Conclusions: Results of this research were unable to prove or disprove the hypothesis regarding 5% agreement of ion chamber and film dose measurements. Results also proved the hypothesis false for achieving 5% agreement between either ion chamber-measured dose or film-measured dose and dose determined from fluence-scaled Monte Carlo simulations.
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