Monte Carlo applications in external radiotherapy
Radiation therapy by photons is commonly utilized for cancer treatment. Ionising radiation is used to destroy tumour cells by damaging their DNA, making it impossible for these cells to continue to grow and divide. The accuracy of the dose delivery is of great importance. Larger dose causes significant complications in the normal tissue, whereas reduced dose decreases the probability of tumour control. Therefore the treatment is carefully planned. Tumours are diagnosed and localized by 3D imaging techniques and the irradiation of the patient is simulated by advanced software referred as a treatment planning system (TPS). Different simplifications and assumptions are used in the TPS algorithms in order to keep balance between the requirements for fast calculations and for sufficient accuracy of the result. Validation of the results from TPS is highly recommended, particularly in situations of inhomogeneous media and interfaces due to lack of electron equilibrium and incomplete scatter conditions. Conditions of electron disequilibrium are typical for complex treatment techniques such as volumetric modulated arc therapy (VMAT). Thus theoretical validation of the planned dose distribution and experimental validation of treatment deliverability are important part of pre-treatment patient specific quality assurance. The intention of this project is to apply a Monte Carlo method for evaluation of clinical dose distributions in patient geometry based on CT images as well as to simulate the response of cylindrical ionization chambers to high-energy photon beams in case of phantom measurements.