State of art and next challenges in instrumentation for quality control in hadron therapy centres

The in-beam positron emission tomography (PET) is currently the only feasible non-invasive method for in-situ monitoring of tumour treatments with ion beams. It is able of assessing parameters relevant for quality assurance, i.e. the particle range in tissue, the position of the irradiated volume and the local deviations between planned and applied distributions. It was used for the first time for quality assurance at GSI hadron-therapy center since 1997: the acquisition is performed during the irradiation and some minutes afterwards which allows the detection of both short-lived and long-lived isotopes and avoids to move the patient. Moreover we can imagine that such in-line PET could be improved to become an on-line PET in conditions that number of LOR detected (Lines of Responses) is large enough and time of reconstruction is short enough to provide typically an image every tens of seconds. The objectives pursued with the present work are to outline present limitations and future challenges of in-beam PET instrumentation. The aim of Part I is to present the prerequisites for a in-beam PET system as well as recent studies to optimise the detector geometry and its performances (by testing modern gamma ray detectors) as well as data processing methods (including adapted reconstruction methods for PET data).In Part II, in-beam and on-line PET challenges are identified. Performances of new fast scintillators and photodetectors are presented in correlation with expected tasks for an optimal delivered dose monitoring. The need of additional simulations for estimating the feasibility of a real time PET camera is obvious. This part also includes a discussion about the possibility of using gamma prompt radiation as a monitor of the dose inside patient under certain conditions