Detection, quantification and 3D localization of anatomical changes with a helium-beam radiography system based on thin pixelated detectors

The clinical use of ion beams facilitates highly precise treatments of patients suffering from cancer. Utilizing the sharp peak in the depth-dose curve of protons and heavier ions, ion-beam radiotherapy treatments exhibit particularly localized dose distributions compared to conventional modalities. However, they are sensitive to changes such as variations in the patient’s anatomy which can occur over the treatment course of typically several weeks. These changes could be assessed prior to each treatment fraction by employing the ion beam itself to generate an image of the patient’s anatomy from beam’s eye view. Despite extensive efforts over the past decades, no ion-beam radiography system is routinely used in clinics yet. Most ion-imaging prototypes require devices with a large material budget. In order to increase the practicability and foster clinical acceptance, a compact detection system was built from thin silicon pixel detectors. However, the system’s ability to precisely measure the clinically relevant quantity for heterogeneous objects is limited. This thesis experimentally investigates the energy-painting approach eliminating this remaining principal limitation of the detection system based on thin detectors. Energy painting subsequently allows for the acquisition of a helium-beam radiograph of an anthropomorphic phantom, which is evaluated regarding its accuracy and compared to clinically used CT modalities based on X-rays. To extract the position of phantom modifications along the beam direction from single ion-beam projections, the 2.5D imaging method is investigated in simulations and experiments. Overall, the system’s capability to detect, quantify, and localize anatomical changes with high spatial resolution is demonstrated. Consequently, this thesis presents fundamental contributions towards a future clinical application of the compact helium-beam radiography system for low-dose verification of the patient’s anatomy prior to ion-beam radiotherapy treatments.