Title page for ETD etd-0305103-143757


Type of Document Master's Thesis
Author Bruce, Paul Anthony
Author's Email Address pbruce@lsu.edu
URN etd-0305103-143757
Title The Use of the BANG-3 Polymer Gel to Quantify the Three-Dimensional Dose Distribution of IMRT
Degree Master of Science (M.S.)
Department Physics and Astronomy
Advisory Committee
Advisor Name Title
Kenneth Matthews Committee Chair
Mark Williams Committee Member
Oscar Hidalgo Committee Member
Sheldon Johnson Committee Member
Thomas Kirby Committee Member
Keywords
  • gel dosimetry
  • polymer gel
  • gel calibration
  • dose deviation
Date of Defense 2003-02-21
Availability unrestricted
Abstract
The sophistication of radiation therapy delivery techniques at Mary Bird Perkins Cancer Center (MBPCC) creates the need for an advanced dosimetric system that can quantify and verify the dose distributions in three-dimensions. Current dosimetric systems perform this dose analysis in only one or two dimensions. This paper evaluates the application of BANG-3 polymer gel dosimetry to quantify the 3-D dose distribution of Intensity-Modulated Radiation Therapy (IMRT) using a "step and shoot" approach. The gel was irradiated by 10 MV photons at a dose rate of 400 MU/min. Relaxation rate maps were computed from proton density and T2-weighted magnetic resonance images acquired with a GE Horizon 1.5T scanner; scans were performed 5 days and 2 months post-irradiation. The dose distribution within the gel was compared to the dose distribution calculated by the Pinnacle3 planning system. Three techniques were used for analysis: image subtraction, dose-volume analysis and contour analysis. Also, a dose correction factor was used to attempt to correct for excess dose delivered to the gel as the gels were erroneously placed in the treatment room two days prior to irradiation. Corrected 5-day post-irradiation dose maps show reasonable agreement with the Pinnacle3 plan. The absolute measurement error was +/-50 cGy; however, the relative errors were large compared to the total dose of 2 Gy delivered to the gel. Delivering a larger total dose should reduce the relative error to a reasonable magnitude. Exposure to light and other environmental factors caused substantial additional polymerization with time. The results of this project indicate that polymer gel dosimetry could be a useful routine 3D dosimetric technique at MBPCC. However, utilizing a commercial scanning service may simplify use of the gels.
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