@article { author = {Hashemi, S M and Bahreyni, M H and Mohammadi, M and Nasseri, S and Bayani, S and Gholamhosseinian, H and Salek, R and Shahedi, F and Momennezhad, M}, title = {An Empirical Transmitted EPID Dosimetry Method using a Back-Projection Algorithm}, journal = {Journal of Biomedical Physics and Engineering}, volume = {9}, number = {5}, pages = {551-558}, year = {2019}, publisher = {Shiraz University of Medical Sciences}, issn = {2251-7200}, eissn = {2251-7200}, doi = {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}, url = {https://jbpe.sums.ac.ir/article_45725.html}, eprint = {https://jbpe.sums.ac.ir/article_45725_be0e729814850502df63019abdc83b3a.pdf} }