Studies for a proton tomography scanner

iMPACT, innovative Medical Proton Achromatic Calorimeter and Tracker, is a University of Padova and INFN project, funded by the European Research Council. The project aim is to design, develop and prototype an extremely fast and accurate proton Computed Tomography Scanner, with the ultimate goal of enabling the realization of a clinically viable proton Computed Tomography (pCT) system. Proton Computed Tomography is an extremely promising technique able to reconstruct density maps (images) of the human body with minimal dose release and high tissue density accuracy, a particularly critical feature in cancer hadron-therapy treatment planning. Hadron-therapy is a leading edge technique where protons or heavy-ions, instead of X-rays, are used to target and destroy the tumor within the human body. By exploiting the peculiar energy deposition distribution such highly ionizing, heavy particles exhibit, it is in fact possible to confine within a volume of few mm3 most of the energy released, hence sparing the healthy tissues surrounding the tumor. However, despite all its beneficial aspects, hadron-therapy is not yet widespread as other more established procedures, such as X-ray therapy. One of the reasons is that the current X-ray Computed Tomography (X-ray CT), currently used to produce body density maps, cannot deliver maps accurate enough to exploit the intrinsic accuracy of the hadron treatment. To precisely aim the hadron energy release with millimeter precision, it is in fact necessary to possess very accurate knowledge of the density it traverse before reaching the tumor. The idea standing behind the development of a pCT scanner is that using the same energy loss behaviour for both the imaging process and the treatment would improve the performance of the latter, the physical interaction process being the same. Currently, several pCT scanner prototypes are being developed around the world; pCT scanner technology however is still far from being applicable in a clinical environment, mainly due to the slow acquisition rates. The iMPACT project therefore plans to develop a pCT scanner able to overcome such limitations, leading the way toward medically sound apparatuses. This thesis work begins by displaying both limitations and advantages of the hadron-therapy technique; the pCT state-of-the-art is then reviewed, highlighting positive features as well as constraints that limit its applicability. The current state of the iMPACT scanner, which embeds a tracker system and a calorimeter, is illustrated and discussed. The thesis then focuses on the development of the calorimeter part of the scanner. The development of a Monte Carlo simulation is presented together with a calibration procedure based on data collected at proton beam tests. Additional studies with proton data are presented with an outlook on future developments.