Evaluation of Dose Distribution at the Level of Electronic Portal Imaging Device using Treatment Planning System

Background: Treatment Planning Systems (TPS) are designed to calculate dose distributions within the CT imaging field of view. However, the Electronic Portal Imaging Device (EPID) is positioned outside this area, making it challenging to use standard TPS for dose calculations at the EPID level.Objective: The objective of this study is to present an innovative approach to address the limitations of TPS in calculating dose distribution at the EPID level.Material and Methods: In this retrospective quantitative study, the CT image was extended to the EPID level and imported into the TPS. ۴۲ treatments were planned, and doses were calculated. The TPS doses were then compared with the measured doses obtained using an Ion Chamber (IC). The study also investigated the impact of field size, phantom thickness, and air gap for energies of ۶, ۱۰, and ۱۵ MV.Results: The average, minimum, and maximum dose differences were ۱.۹۱%, ۰.۰۲%, and ۵.۷۹% when changing the field size from ۵×۵ cm۲ to ۲۰×۲۰ cm۲, ۳.۶۲%, ۰.۱۸%, and ۶.۹۱% when the phantom thickness changed from ۱۰ to ۳۰ cm, and ۳.۵%, ۰.۴%, and ۷.۴۶% when the air gap was varied from ۳۰ to ۶۰ cm respectively. ۹۷% of all changes in IC values can be predicted through the linear relationship with TPS. Conclusion: The validated proposed method in this study, as an innovative approach, effectively addresses the limitation of TPS in calculating dose distribution at the EPID level. This can be used as a reference for comparing the measured dose obtained by EPID in dosimetric verification.

کلیدواژه ها:

Radiotherapy ، Radiotherapy Setup Errors ، Radiation dosimetry ، Electronic Portal Imaging Device ، Treatment planning system