In-Beam Imaging Tests of the Small OpenPET Prototype with Radioactive Beam Irradiation

Introduction: The OpenPET geometry is our original idea to visualize a physically opened space between two detector rings. One of our targets is in-beam PET, which is a method for in situ monitoring of particle therapy. We expect the OpenPET will be the first practical 3D geometry to be realized, as conventional systems using positron cameras are basically limited to 2D imaging. We have previously developed a small prototype to show a proof-of-concept of in-beam imaging in the Heavy Ion Medical Accelerator in Chiba (HIMAC). In this paper, we evaluated imaging performance of the small OpenPET prototype for carbon ion therapy.Materials and Methods: The OpenPET prototype (two detector rings of 110 mm diameter separated by a gap of 42 mm) was positioned so that the beam passed through the gap. For the usual carbon beam irradiation, the activity of produced positron emitters is generally low, in addition to there being a theoretical difference between the dose distribution and positron emitter distribution. Therefore direct irradiation of radioactive beams is ideal for in-beam PET. In this paper, in addition to 11C, we used a 10C beam, whose half-life is about 19 s. As targets, in addition to a rectangular parallelepiped PMMA phantom, we used F344 rats in order to observe the washout effect.Results and Discussion: Imaging results showed that PET images directly corresponding to the distribution of primary particles were obtained by the radioactive beam irradiation. In particular, a much higher activity concentration was seen in the 10C beam irradiation than that in the 11C beam irradiation. For rats, with 97 s PET measurement after 2 s 10C irradiation, activity ratios remained in the brain and the thigh muscle were 48% and 81%, respectively. Feasibility of in-beam OpenPET imaging was shown not only for phantoms but also for a living body.2012 World Congress on Medical Physics and Biomedical Engineerin