Intercomparison between two commercial EPID-based in vivo dosimetry systems

In vivo dosimetry in external beam radiotherapy has undergone significant evolution over the past decades, transitioning from thermoluminescent dosimeter-based techniques to advanced systems employing digital detectors and complex dose reconstruction algorithms. Despite these advancements, current challenges include improving dosimetric accuracy and the real-time detection of dose and setup errors, as well as enhancing the practicality of these techniques for implementation and clinical use. This thesis explores the characteristics of two commercial EPID-based in vivo dosimetry systems, starting from a study of the algorithms used for dosimetric purpose, and concluding with initial tests on phantoms to determine their reliability and suitability for clinical practice. The study also reports the procedures and measures that have been necessary for the implementation, calibration, and characterization of the two systems. The developed method for testing the systems relies on performing clinically representative treatments on an anthropomorphic phantom and comparing the dose measurements taken with the EPID to those taken with a cylindrical phantom during treatments delivered to the latter. The accuracy of in vivo dose reconstruction and the ability to detect errors in phantoms positioning have been evaluated. This study played a key role in understanding the potential and limitations of the two systems, based on different dosimetric principles, and enabled us to optimally employ them to improve the quality of radiotherapy treatments in our center.