The use of prompt γ-rays for in-vivo dosimetry at therapeutic proton and ion beams

Radiation therapy is an important treatment modality in cancer therapy. New radiation species like protons and light ions have the potential of increasing tumor conformity of the irradiation. These particle beams offer advantages over conventional treatment modalities, such as photons. Because of the way particles deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the damage to the surrounding healthy tissue. However, the parameters of the ion beams must be calculated from X-ray CT data using a physical beam model. Minor inaccuracies of imaging and modeling and small changes in the irradiated volume will lead to a mismatch of the deposited dose maximum and the tumor. This causes missing dose in the tumor volume and potential damage to healthy tissue. Thus, to use the advantages of particle therapy to full capacity, proton and ion beam radiotherapy treatment requires efficient quality assurance techniques for dose delivery monitoring. Until now, the only clinically applied in-vivo dosimetry method for ion beams is PET. However, this method suffers from inherent physical limitations. Therefore, a new approach based on the detection of prompt gamma rays is under development. A Compton camera seems to be a feasible technical solution for monitoring proton and ion irradiation. Our project is aimed to design and construct such a camera, and evaluate if it could lead to clinical applications. This comprises the whole simulation process, i.e. simulating the expected gamma-emissions from the treatment plan, the reconstruction and the assembly of a prototype as well as the simulation of the detector efficiency.