Dosimetric Verification Of Intensity Modulated Radiation Therapy Treatment Plans With Gafchromic Ebt Film Using 6 Mv Photons

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Date
2010-09
Authors
Cheng, Soon Keong
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Publisher
Universiti Sains Malaysia
Abstract
In this project, Gafchromic film (type EBT) as an evaluation tool for quality assurance was studied. The dosimetric features of a EBT film was analysed before it was used in IMRT dose verifications. The film was scanned using an Epson V700 document scanner and then analysed using Image-J and Omni-pro softwares. The characteristics of the scanner using these softwares were also evaluated. The film was calibrated using optical density against dose in the dose range used in IMRT radiotherapy at the Mount Miriam Cancer hospital. The study has shown that the Gafchromic EBT film is suitable as a dose measurement dosemeter as it was energy, field size and angular independent. However calibration of optical density against dose had a polynomial curve relationship. A standard protocol was created for the hospital to standarize the procedure and verification process using the scanner and software Image-J as well as Omni-pro. For five IMRT plans, dose plans from TPS and Gafchromic EBT film, a mean value of 86.65 % with a standard deviation of 4.2 % was obtained at the gamma criteria of 3 % / 3 mm DTA. For another 5 IMRT plans, dose plans from TPS versus Gafchromic EBT film and 2D-array MatriXX, gave 88.30 % for Gafchromic EBT film while 2-D array MatriXX gave 94.71 % at the gamma criteria of 3 % / 3 mm DTA. As a conclusion, film dosimetry presents a high spatial resolution for IMRT verification within an accuracy of ±3 % and the confidence level of 88% was standardized as passing criteria for IMRT QA before the patient treatment can proceed. However in certain cases where there are high dose gradients, the confidence level has to be modified to achieve ±3 %.
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Keywords
Intensity Modulated Radiation Therapy , Gafchromic Ebt Film Using 6 Mv Photons
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