Particle imaging for daily in-room image guidance in particle therapy

Particle therapy exploits the highly localized depth dose profile of protons and light ions to deliver a high dose to the target while largely sparing surrounding healthy tissue. The steep dose gradient at the end of the ions range, known as the Bragg peak, however, also makes particle therapy sensitive to range uncertainties. In current clinical practice, a major cause of range uncertainties resides in the conversion of the treatment planning x-ray CT to the patient specific relative stopping power (RSP) map that is crucial for accurate treatment planning. By measuring the energy loss of particles after traversing the patient, particle imaging enables a more direct reconstruction of the RSP. In this thesis, different aspects towards the clinical implementation of particle imaging are investigated. First, a theoretical description of the point-spread function for different particle radiography algorithms is developed in order to explain observed limitations. A novel filtering technique to remove nuclear interaction events in particle imaging is proposed and high quality experimental helium ion CTs are demonstrated. First results from an experimental comparison between particle and x-ray CT modalities for RSP prediction in animal tissue samples are presented. Furthermore, a novel technique for intra-treatment helium ion imaging based on a mixed helium/carbon beam is explored with that relative range changes in the millimeter regime were observable. Finally, novel particle imaging detector designs are investigated. The thesis highlights the potential of helium ion imaging for pre- and intra-treatment image guidance in particle therapy