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

S M Hashemi, M H Bahreyni, M Mohammadi, S Nasseri, S Bayani, H Gholamhosseinian, R Salek, F Shahedi, M Momennezhad


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.


Radiotherapy Planning, Computer-Assisted ● Dose-Response Relationship ● Radiotherapy ● Algorithms

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eISSN: 2251-7200        JBPE NLM ID: 101589641

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                                                                        Chairman and Editor in Chief

                                                                              Dr. Alireza Mehdizadeh

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