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Published on: May 2, 2018
An Empirical Transmitted EPID Dosimetry Method using a Back-Projection Algorithm
Hashemi S M1, Bahreyni M H1, Mohammadi M2,3
1PhD, Medical Physics Research Center, Mashhad University of medical Science, Mashhad, Iran.
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.
