| Περίληψη: | The treatment process of external beam radiation therapy of tumors inevitably introduces geometrical uncertainties. These errors might be introduced during the preparation phase of the treatment (systematic errors), or during the execution of the treatment (random errors). Investigating the errors and assessing their magnitude is a prerequisite for the quantification of the required margin by which the Clinical Target Volume (CTV) must be expanded in order for the Planning Target Volume (PTV) to be acquired.
In this thesis, the required PTV margins were calculated for the radiotherapy departments of three major Greek hospitals: the University Hospital of Patras, the University Hospital of Larissa and the Theageneio Anticancer Hospital of Thessaloniki. Specifically, the protocols followed by each department were studied and reviewed, the sources of all geometrical uncertainties throughout the course of radiotherapy were investigated, the errors were calculated, the required PTV margins were quantified per anatomical site for each hospital and a comparison of the results between the departments was made.
In total, data from 278 patients and 2094 CBCT scans were recorded, studied and reviewed. Four different methods of statistical processing of the data were suggested for the computation of the setup error, with two of them being introduced by this thesis as the most representative for departments that follow a hybrid correction strategy protocol. Moreover, a simple and practical method for the assessment of organ motion was introduced and suggested, using the vendor image registration software available in our departments. Also, the delineation error of several anatomical sites was found, on the basis of a delineation experiment conducted in the departments of Patras and Larissa with the participation of the physicians. Finally, a comparison of the results between the three departments allowed for the extraction of useful conclusions regarding the operation of each department, as well as for the formulation of suggestions regarding protocol optimization in order to succeed the limitation of errors and the reduction of the required PTV margins.
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