Journal of Biomedical Physics and Engineering

An Empirical Transmitted EPID Dosimetry Method using a Back-Projection Algorithm

Document Type : Original Research

Authors

S M Hashemi 1
M H Bahreyni 1
M Mohammadi 2, 3
S Nasseri 1
S Bayani 4
H Gholamhosseinian 1
R Salek 5
F Shahedi 6
M Momennezhad 1, 7

1 PhD, Medical Physics Research Center, Mashhad University of medical Science, Mashhad, Iran

2 PhD, Department of Medical Physics, Royal Adelaide Hospital, Adelaide, SA 5000, Australia

3 PhD, School of Physical Sciences, University of Adelaide, Adelaide, SA 5005, Australia

4 MSc, Medical Physics Research Center, Mashhad University of medical Science, Mashhad, Iran

5 MD, Cancer Research Center, Mashhad University of medical Science, Mashhad, Iran

6 MSc, Department of Radiology, School of Paramedical Sciences, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran

7 PhD, Nuclear Medicine Research Center, Mashhad University of medical Science, Mashhad, Iran

10.31661/jbpe.v0i0.1082
Abstract
Background: The present study aimed to introduce a rapid transmission dosimetry through an electronic portal-imaging device (EPID) to achieve two-dimensional (2D) dose distribution for homogenous environments.
Material and Methods: In this Phantom study, first, the EPID calibration curve and correction coefficients for field size were obtained from EPID and ionization chamber. Second, the EPID off-axis pixel response was measured, and the grey-scale image of the EPID was converted into portal dose image using the calibration curve. Next, the scattering contribution was calculated to obtain the primary dose. Then, by means of a verified back-projection algorithm and the Scatter-to-Primary dose ratio, a 2D dose distribution at the mid-plane was obtained.
Results: The results obtained from comparing the transmitted EPID dosimetry to the calculated dose, using commercial treatment planning system with gamma function while there is 3% dose difference and 3mm distance to agreement criteria, were in a good agreement. In addition, the pass rates of γ < 1 was 94.89% for the homogeneous volumes.
Conclusion: Based on the results, the method proposed can be used in EPID dosimetry.

Keywords

Radiotherapy Planning, Computer-Assisted
Dose-Response Relationship
Radiotherapy
Algorithms
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Journal of Biomedical Physics and Engineering
Volume 9, Issue 5
35
October 2019
Pages 551-558

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