Small field photon dosimetry and Monte Carlo simulation

In this thesis study, dosimetric data of a 6 MV photon beam with small field sizes used in advanced treatment techniques such as intensity-modulated radiotherapy, volumetric-modulated arc therapy, stereotactic radiosurgery, etc., were measured with different detectors. The aim was to compare these data with simulation data generated using Monte Carlo (MC) codes. The study investigated the effect of the reference detector on measurements. Different detectors were used as the reference detector to obtain percent depth dose and profile curves for 1x1 and 5x5 cm² fields. The dosimetric data obtained by using different detectors as the reference detector at different positions were evaluated, and the type and position of the reference detector were determined. For different field sizes of 10x10, 5x5, 4x4, 3x3, 2x2, and 1x1 cm², percent depth dose measurements were performed in a water phantom using Semiflex, Pinpoint ion chambers, and Edge, diodeSRS, microDiamond detectors with different volumes and characteristics. Five different detectors were used with different measurement setups to obtain X and Y-axis profiles at dmax (1.5 cm), 5 cm, and 10 cm depths. Relative dose factor (RDF) measurements were performed with three different detectors (Semiflex, Pinpoint, Edge), and the obtained values were compared with the values obtained from MC. Measurements were carried out with different detectors for 10x10, 5x5, 4x4, 3x3, 2x2, and 1x1 cm² field sizes, as before. In conclusion, the aim of this study was to measure dosimetric data of small field sizes for a 6 MV photon beam using different detectors and compare these data with Monte Carlo simulation. This study is important for the accurate introduction of dosimetric data of treatment devices into the treatment planning system and ensuring the accuracy of dosimetric data used in the treatment of radiotherapy patients.