Development of a positron emission tomograph for “in-vivo” dosimetry in hadrontherapy

This thesis is related to the DoPET project, which aims to evaluate the feasibility of a dedicated Positron Emission Tomograph (PET) for measuring, monitoring, and verifying the radiation dose that is being delivered to the patient during hadrontherapy. Radiation therapy with protons and heavier ions is becoming a more common treatment option, with many new centers under construction or at planning stage worldwide. The main physical advantage of these new treatment modalities is the high selectivity in the dose delivery: very little dose is deposited in healthy tissues beyond the particles’ range. However, in clinical practice the beam path in the patient is not exactly known. This affects the quality of the treatment planning, and may compromise the translation of the physical advantage into a clinical benefit. The use of a PET system immediately after the therapeutical irradiation (“in-beam”) for in-vivo imaging of the tissue + activation produced by nuclear reactions of the ion beam with the target, could help to have a better control of the treatment delivery. The DoPET project, based on an Italian INFN collaboration, aims to explore one possible approach to the hadron-driven PET technique, through the development of a dedicated device. Such goal was reached through the validation of a PET prototype with proton irradiations on plastic phantoms at the CATANA proton therapy facility (LNS-INFN, Catania, Italy) and with carbon irradiations on plastic phantoms at the GSI synchrotron (Darmstadt, Germany). A preliminary comparison with an existing in-beam PET device was also performed. The candidate was involved with all aspects of this project, specifically the Monte Carlo simulations of the physical processes at the basis of phantom activation, the measurements for the characterization of the DoPET detector, the improvement of the image reconstruction algorithm, and the extensive measurements in plastic phantoms. The system and the methods described in this thesis have to be considered as a proof of principle, and the promising results justify a larger effort for the construction of a clinical system.