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Abstract

Abdominal organ motion compromises the targeting accuracy of proton therapy of pancreatic cancer. Time-resolved volumetric magnetic resonance imaging (4D-MRI) is a promising technology to visualize organ motion and deformation while providing a high soft-tissue contrast and avoiding additional imaging doses. The aim of this thesis is to quantify motion-induced impacts on dosimetry, based on 4D-MRI, and to determine suitable strategies to improve the treatments. For this purpose, a method was developed that utilizes repeated 4D-MRI measurements to analyze motion-induced impacts on dosimetry along the treatment course in proton therapy. The clinical impact of organ motion was evaluated in a patient cohort by statistical analyses. Moreover, counter-strategies to mitigate the motion-induced dosimetric impacts were investigated using abdominal corsets or beam-gating. Fractionation helps to reduce the motion-induced tumor underdosage substantially. However, especially for patients with large motion amplitudes, further motion mitigation may be required. Physical compression by abdominal corsets and beam-gating with certain pre-selected gating criteria showed high potential to improve the dose distributions. The developed method allows an effective evaluation of the motion-induced dosimetric uncertainties and is applicable in both pre-treatment and prospective real-time MR-guided proton therapy scenarios with online MR imaging during irradiation.