Introduction: Radiotherapy is one of the three basic ways of treating cancer in which ionizing radiation is used to achieve a therapeutic effect. The goal of treatment is to deliver a precisely determined dose of radiation to a predetermined tumor target volume of tissue with as little damage to healthy tissue as possible. In the past, lead blocks and individual protections were used to design irradiation fields, but today a multi-leaf collimator system (MLC system) is used. MLC system is an integral part of a linear accelerator and usually consists of 120 or 160 tungsten leaflets configured in pairs. Important features of MLC systems are: leaf thickness, leaf and interleaf transmission, number of leaflets and leaflet speed. Purpose: The purpose of this diploma thesis is to present, through a systematic review of the literature, what MLC systems for the design of irradiation fields in a linear accelerator were used in the past, and what systems are in use today. The main goal is to define and clarify the development of the MLC system in radiotherapy and its contribution to patients whose cancer is treated with radiation through a systematic review of the literature. Methods: In the diploma work we used a descriptive method with a systematic review of the literature. We focused on the literature in the field of MLC systems in radiotherapy, how their development took place, what are their properties, development and innovations in the field of planning in radiotherapy. We searched for the mentioned literature from October 2019 to March 2020 in Slovenian and international bibliographic databases. Results: We have presented all the findings of the articles used for the systematic review. All the parameters of MLC systems were being developed with strong emphasis being on reducing the leaf thickness, transmission over the leaves and in increasing leaflet speed. MLC localization systems have also been developed. Discussion and conclusion: We found that all the parameters whose development we presented were greatly improved. The thickness of the leaflets decreased from 1 cm or more to 5 mm or less, the number of leaflets increased from 80 to 120 or 160, the leaf transmission decreased to less than 1%, the speed of leaflet movement increased from 1 cm/s up to 5 cm/s. All of these improvements have contributed to better results of radiotherapy.
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