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
Journal Title
Journal ISSN
Volume Title
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 %.
Description
Keywords
Intensity Modulated Radiation Therapy , Gafchromic Ebt Film Using 6 Mv Photons