Identifier

etd-0305103-143757

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

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.

Date

2003

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Kenneth Matthews

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