Theoretical and numerical analysis of the single-ring OpenPET geometry for in-beam PET

We are developing the OpenPET, an open type PET geometry having an accessible and observable open space between detector rings which allows easy access to a patient during PET measurements. Our first generation OpenPET which we called dual-ring OpenPET consisted of two detector rings having a gap between them and it could provide an extended axial field of view (FOV). For applications such as in-beam PET to monitor dose distribution in situ during particle therapy, however, higher sensitivity is required rather than a wide FOV. As the next generation OpenPET, we proposed the single-ring OpenPET which was a geometry having an accessible and observable open space with higher sensitivity and a reduced number of detectors than the earlier geometry. In this paper, we provide a theoretical analysis of the sensitivity for the single-ring OpenPET and we compare it with the dual-ring OpenPET and a geometry in which the conventional PET is positioned at a slant angle against the patient bed to form an accessible open space, which we called slant PET. The theoretical analysis shows that the single-ring OpenPET has a sensitivity 1.2 times higher than the dual-ring OpenPET and 1.3 times higher than the slant PET when designed for about 200 detector blocks, each with a front area of 2500 mm². In addition, numerical simulation using the Geant4 Monte Carlo toolkit is done to show the three-dimensional imaging performance that the single-ring OpenPET realized with the ellipsoidal rings of block detectors. The numerical simulation demonstrates that the depth-of-interaction detector can provide uniform resolution even when the detectors are arranged in an ellipsoidal ring.