Investigation of convenience testing steps of model-basedtreatment planning system in radiotherapy in terms oftwo- and three-dimensional criteria

Radiotherapy is a fundamental treatment modality in cancer therapy, aiming to deliver a therapeutic dose of ionizing radiation to the target tumor volume while maximizing the preservation of surrounding healthy tissues. Achieving this goal successfully requires high accuracy in the dose calculation algorithms utilized by treatment planning systems, which is of critical importance. The integration of model-based TPS in clinical radiotherapy has become feasible with advances in computer technology, particularly through the development of multi-core parallel processing, which has enabled the implementation of fast and accurate Monte Carlo (MC) methods. The success of radiation therapy depends on maximizing tumor control probability while minimizing normal tissue complication probability—both of which are directly influenced by the absorbed dose in tumor and healthy tissues. Therefore, accurate dose distribution within the patient is of paramount importance. Before clinical implementation, TPS must undergo commissioning and validation in accordance with international protocols and technique-specific evaluation criteria. In advanced radiotherapy techniques such as Intensity-Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT), the increasing use of small fields and high dose gradients necessitates the inclusion of post-modeling validation steps. Following MC-based modeling in the TPS, verification of the model is recommended as part of a standardized post-modeling procedure. In this context, validation of the Monte Carlo photon beam model in the TPS—specifically its geometric and dynamic multileaf collimator (MLC) parameters—should be performed by comparing dose distributions with 2D measurements obtained from a series of test plans on linear accelerators (LINAC) operating at different energy levels. In this thesis, Monte Carlo-based dose distribution calculations were performed in the Monaco® 5.11 TPS for two different LINAC devices equipped with Elekta Agility™ MLC head structures and operating at various photon energies. Test plans were generated using the Source-to-Axis Distance (SAD) technique with a 1 mm dose grid size and 0.5% statistical uncertainty, producing both two-dimensional (2D) and three-dimensional (3D) dose distributions for both flattened and flattening filter-free (FFF) photon beams. Dose measurements were acquired using software-supported Octavius and Dolphin 2D detector array systems. Measurement and calculation data were analyzed via gamma evaluation using 2% dose difference and 2 mm distance-to-agreement criteria, with a passing rate of 95% achieved in both 2D and 3D analyses. The findings contribute to the refinement of model parameters in Monte Carlo-based TPSs, enhancing the accuracy and reliability of future radiotherapy treatment plans. These results represent a significant step toward improving the precision of Monte Carlo-based treatment planning systems by optimizing essential modeling parameters and thereby supporting the delivery of highly accurate and clinically reliable radiation therapy.