Monte-Carlo-Simulationen zur Referenzdosimetrie hochenergetischer Photonen und Elektronenstrahlung in der Radioonkologie

In recent years, new irradiation techniques (intensity modulated radiation therapy, rapid arc, stereotaxy or irradiation on a flattening filter free linear accelerator) established successful in radiooncology, which entail a constant adaptation and expansion to quality assurance requirements. An essential code of practice for radiation therapy is DIN 6800-2, which defines the basic requirements and correction factors for the dosimetry of high-energy X-ray and electron radiation. In clinical reference dosimetry according to DIN 6800-2, mostly air-filled ionization chambers or solid-state detectors are used. These are previously calibrated in a calibration laboratory in accordance with reference conditions and later adapted to the measurement conditions. Monte Carlo simulations are a common procedure in medical physics for improving quality assurance. With this numerical approach, the complex beam transport in matter can be understood. Furthermore, experimental investigations can be verified or correction and perturbation factors can be calculated for different detector types. This cumulative dissertation presents new results from the field of reference dosimetry using Monte Carlo simulation for high-energy photons and electron radiation. The peer-review publications from the field of electron dosimetry with ionization chambers present new results which revise the assumptions of the code of practice in relation to fluence disturbance. Furthermore, the concept of positioning in the effective point of measuring for parallel plate chambers in high-energy photon radiation and electron radiation was extended and revised. In the second part of this thesis, solid-state alanine dosimeters were investigated and correction factors for their application in high-energy photons and 192Ir radiation were presented. Based on these results, the response of alanine dosimeters was investigated as a function of the measurement environment material and applied in a clinical study. The results of this work represent a further step in the continuous improvement of quality assurance in radiation therapy. In addition to the optimization of already established procedures, a contribution to the development of a new dosimetric secondary standard has been made.