Thesis defense of Isabelle Schilling

The effort to obtain continual progress in treatment quality in proton therapy facilities implies new technical requirements, mainly for the irradiation machines and the detector systems. For example, the collimation of proton spots generates stepper dose gradients and, thereby, the need for detectors with a high spatial resolution. Besides this, beam currents around 2 nA (≈ 1.2 ⋅ 1010 protons s ) during patient treatment set challenging requirements on the detectors’ readout electronics for single particle tracking or counting. The knowledge gained in detector development in High Energy Physics (HEP) during the past decades is transferred to proton therapy applications in this work to address the upcoming detector requirements. It provides studies investigating the usage of a pixel detector designed for individual particle tracking in the high-radiation environment of the ATLAS experiment at LHC, namely the ATLAS IBL Pixel Detector, for proton beam measurements at proton therapy facilities. Due to the small pixel size of the detector under study, the shape of single pencil beam proton spots is determined with precision in the smaller pixel direction of 28 μm. The timing information of the particle hits on the detector allows the distinction between the single spots of scanned proton fields. Dose linearity checks reveal that the detector meets the requirement of an output dose consistency of ± 3 % for the daily quality assurance (QA) in the chosen dose range. Additionally, further studies lead to the conservative assumption that hit rates up to (73.85 ± 0.95) clusters 25 ns sampled with a frequency of 1 kHz feature a linear dependency on the beam current. Furthermore, the provided information on the deposited energy in the detector is utilized for range verification. Range differences of 1 mm required for the daily QA can be detected for proton energies impinging the sensor in the range of (30 − 44) MeV. Finally, an example of using the detector under study in the field of proton therapy is given by supporting a study investigating the energy deposition of platinum nanoparticles on a macroscopic scale. This work offers a characterization of the ATLAS IBL Pixel detector for proton therapy application and points out improvement opportunities for further detector development.

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