Characterization of an "In-Beam" PET Prototype for Proton Therapy with Different Target Compositions

Ion treatment can deliver an accurate and effective therapy. The verification of the delivered dose, after each irradiation, is an information that can improve the effectiveness of the complete treatment, if a comparison of the planned with the delivered dose is foreseen. A possible way to do this verification is measuring the beta+ emitters, like 11-C, 15-O, 10-C that are generated in irradiated tissues by nuclear reactions, by using a positron emission tomography (PET) system. We have realized a PET prototype based on two planar heads; each head is made up of a position sensitive photomultiplier coupled to a square matrix of same size of LYSO scintillating crystals (2x2x18 mm3 pixel dimensions for a total area of 5x5 cm2). A special resistive chain and a dedicated electronic board that performs signal amplification and digitization were realized. A 3D Maximum Likelihood Expectation Maximization reconstruction program that uses all of the collected lines-of-response was implemented. This prototype was tested at the INFN-LNS proton facility in Catania (Italy), where clinical treatment of ocular pathologies in patients is performed. In this paper we present: the results obtained for the range monitoring in monoenergetic and extended proton irradiations of homogeneous PMMA cylinders; the dependence on different density values and stoichiometry with inhomogeneous phantoms; the spatial relationship between the dose distribution and its PET image.