Introduction: Prostate cancer is the most common cancer in men in Europe and Slovenia. The size of the safety margin affects the dose received by the critical organs. Therefore, the safety margin needs to be thoroughly defined when making a radiation plan. All the physiological movements of the prostate, changes in the size of the prostate and the deviations in the patient`s radiation position setting need to be taken into account. It is important to prevent the intrafractional motions, which are defined as movements within each fraction of radiation. Purpose: In our diploma work we wanted to figure out the movement differences between bone structures and soft prostate`s tissue in x, y and z directions in different patients. We also measured the differences between each of these directions for every patient. Methods: We collected data on movements in 14 patients with inserted golden markers, which radically treated their prostate cancer on linear accelerator Versa HD (Elekta) at the institute of oncology in Ljubljana. For analysis and evaluation of the data we used Microsoft Excel 2016 and IBM SPSS Statistics 24. Results: From our data and statistical analysis we found out that movement differences between bone structures and soft prostate`s tissue are the smallest from the x directions, because none of the differences exceeded the planned safety margin (5–7 mm). But there is a small percentage of movement differences in y and z directions, which exceeded the planned safety margin for radiation of prostate (>7mm). Discussion and conclusion: Bigger movements in y and z directions may occur due to different bladder or rectum loading, the patient's relaxation, and changes in the shape of the organ before the preparation for radiation on computed tomography (CT) simulator, during preparation for radiation and/or when radiation is in session.
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