Status of the Development of a Single γ -ray Imaging System for in-vivo Dosimetry at Particle Beams

Ion beams offer advantages over conventional treatment modalities, such as photons. Because of the way ions deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the collateral damage to the surrounding healthy tissue. However, small changes in the irradiated volume will lead to a misalignment of the deposited dose maximum and the tumor. Therefore, a dose monitoring system is highly desirable. Positron Emission Tomography (PET) was clinically applied for example between 1997 and 2008 at the GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt, Germany, for monitoring the dose delivered by 12-C beams. Due to inherent limitations of this method, a direct quantification of the delivered dose is not feasible. Therefore, another approach currently under investigation monitors the dose by means of the detection of prompt $\gamma$-rays. A Compton camera may be a feasible technical solution for such a monitoring system. To set up a clinical monitoring system a comprehensive simulation of the creation of secondary radiation as well as of the detection process is required. Furthermore, a sophisticated reconstruction of the data is essential. This paper will show the capability of the reconstruction to image also events measured by means of a Compton camera gamma-rays having energies of 4.4 MeV.