| Περίληψη: | In modern radiotherapy treatment methods, the complexity has increased rapidly and this leads to the need of a more precise quality assurance program (QA) to verify whether the treatment plan can be delivered to the patient properly. This thesis is focused on how the system that is used in our clinic, University Hospital of Patras, for the QA process the Delta4 phantom dosimeter can become more efficient by reducing the deviations between measured and calculated doses. Initially, this was achieved by conducting a literature study, were articles and studies about the function of Delta 4 were investigated in order to find ideas and solutions to the deviations problem. The conclusion was that the most appropriate workflow was to test and repeat all the major processes again. The first task was to do a recalibration and a configuration of the Delta4 as meticulous as possible. After these processes were completed the validation and evaluation of Delta4, Monaco treatment planning system and linear accelerator took place through several procedures for simple (non-IMRT) and complex (IMRT) plans. Having asserted that all three components of radiotherapy QA (the calculation, the delivery and the measurement) were operating correctly we proceeded to the second part of this thesis in order to establish a method to reduce the reported deviations. For this purpose, again a literature study was conducted in conjunction with an idea that we had thought during the experiments. The proposed solution from this thesis is the calculation of a correction factor that will include and correct both the deviations originated from the daily output of the Linac and any systematic error originating from the commissioning and calibration of the measuring instrument. Two methods were considered for the calculation of this correction factor and are analytically presented. Lastly, the use of a different electron density value for the Monaco calculations, that was proposed in the literature, was examined.
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