Identifier

etd-10132004-211301

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

Abstract

Different techniques have been developed and used to evaluate dose distribution calculation accuracy and dose delivery reproducibility as a part of patient-specific IMRT QA – e.q. film dosimetry, ionization chambers, and diode arrays. To verify that the calculated dose distribution is delivered accurately during treatment, film dosimetry is usually used. The accuracy and reproducibility of film optical density as an indicator of dose is influenced by several variables, including the chemical processing and scanning conditions. This study investigates the possibility to use a desktop computed radiography (CR) system for patient-specific intensity modulated radiation therapy (IMRT) quality assurance (QA). A study was done at Mary Bird Perkins Cancer Center, Baton Rouge, LA; where phantom IMRT plans are calculated using an ADAC Pinnacle3 treatment planning system. A Kodak ACR-2000i system is used for the study together with Kodak flexible phosphor screens (plates). In this study, 778 CR plate exposures were done. Several tests were performed including evaluation of the CR plate response dependency when exposed to changes in either setup or scan conditions. Calibration curves were generated for three different energies: 4 MV, 6 MV and 10 MV. Using these calibration curves, the CR plates’ response and behavior as an IMRT tool was analyzed using 10 different patients’ IMRT plans for each energy with approximately 7 fields per patient. Analysis of film was done with commercial IMRT analysis software. Analysis of CR plate data was done in IDL (Research Systems, Inc.), with programs written in house, and included several separate algorithms including automatic image registration. This algorithm uses the Fourier-Mellin transform for automatic image registration. It was found that CR plates showed generally good agreement with the planned values with some significant over-response in the low dose regions, which can be reduced by filtration and improved calibration curves. In view of the results presented, a CR system stands as a potentially fast and practical tool for IMRT patient-specific treatment QA.

Date

2004

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Oscar Hidalgo-Salvatierra

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