Ion imaging using novel ultra-fast silicon detectors

In addition to chemotherapy and surgical interventions, radiation therapy is an important pillar of the treatment of malignant tumour diseases by depositing high amounts of energy in the tumour to kill the cancer cells. Irradiation can be performed either with photons, electrons or ions. Although irradiation with ions is technically very complex, it has become established in recent years for special types of tumours. Ion beam therapy, as any treatment modality, relies on a treatment plan based on accurate estimation of the tissue the used particles have to traverse to reach the tumour. This treatment plan is currently based on X-ray computed tomography (CT), even tough the treatment is performed with ions, which are underlying fundamentally different interactions than X-rays. Ion computed tomography (iCT) is a novel imaging modality that aims to improve the treatment planning quality in ion beam therapy. It uses accelerator-produced ion beams to determine the tissue properties on their path to the tumour. In contrast to conventional X-ray computed tomography, iCT could provide more accurate tissue estimates also with less radiation dose due to imaging. Several promising iCT demonstrator systems have emerged over the last few years, which usually determine the tissue properties by measuring energy loss and particle path of ions passing through the patient using a tracking system and a separate residual energy detector. However, iCT is still far from clinical implementation, mainly due to the limitations of current detector designs, especially because of the limited rate capability of the underlying detector technologies. This project aims to address those challenges by investigating a new iCT modality based on time-of-flight (TOF) energy determination using novel ultra-fast silicon detectors. These TOF measurements can be incorporated into the imaging process itself, allowing the construction of a more compact and cost-efficient detector design as the same detector technology can be used for both tracking and the energy loss estimation. In particular, two different scanner designs will be investigated: an iCT with a TOF detector for residual energy determination and a radically new approach, the so-called sandwich TOF-iCT method. While the former uses TOF measurements in air downstream of the patient to determine the residual energy, the latter does not require a residual energy detector as it measures the energy loss indirectly by determining the TOF through the patient. This work will be the first detailed experimental study of both TOF imaging modalities by developing a small demonstrator system at GSI in Germany and first proof-of-concept measurements of this system at the MedAustron research and therapy centre in Austria. As no previous experimental data exists, the obtained results will serve as an important first step to push iCT further towards clinical implementation.