Simulation design of a single-ring OpenPET for in-beam PET

One of the challenging applications of PET is for in-beam PET, which is an in situ monitoring method for charged particle therapy. For this purpose, we have previously proposed an open-type PET scanner, OpenPET. The original OpenPET has a physically opened field-of-view (FOV) between two detector rings which irradiation beams pass through. This dual-ring OpenPET has a wide axial FOV including the gap. Therefore this geometry is not necessarily the most efficient when it is applied to in-beam PET in which only a limited FOV around the irradiation field is required. In this paper, we proposed new single-ring OpenPET geometry as more efficient geometry dedicated to in-beam PET. The detector ring of the proposed geometry is a cylinder both ends of which are cut by parallel aslant planes. The proposed geometry can be made compact so that the beam port can be placed close to the patient. One of the problems for the proposed geometry is arranging the rectangular block detectors. We proposed two arrangement types, a slanted ellipse type where oval detector rings are slanted and stacked and an axial shift type where block detectors originally forming a conventional PET scanner are axially shifted little by little. We compared the two types through numerical simulations. The simulated systems were a small prototype that we designed for a proof-of-concept and a human sized system. We evaluated the effect of utilizing depth-of-interaction (DOI) measurement in both sized system in both types. In the small sized simulations, both types resulted in acceptable image quality with DOI capability. In the human sized simulation, on the other hand, the effect of DOI utilizing was not clearly shown because the size of spots was too large compared with the size of the crystals. Therefore, our future work is further investigation the quality of reconstructed images for both types in the human sized simulation.