Performance evaluation of an OpenPET detector for heavy Ion therapy under actual in-beam condition

OpenPET which consists of two detector rings separated axially is suitable for in-beam PET in heavy ion therapy. Although the primary ion beam do not enter into the PET detector in the OpenPET, light fragment ions from a target can enter into the detectors and could affect the detector performance under the actual in-beam condition. Previously, we demonstrated that the OpenPET detector can be sufficiently operated in off-beam experiments after carbon beam irradiation. In this presentation, we reported the results of in-beam measurements with a prototype OpenPET detector optimized for the in-beam measurement. Experiments were performed in the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences. The OpenPET detector consisted of a 8 × 8 × 4 LGSO crystal array and a 64-channel PS-PMT. The size of the crystals was 2.9mm × 2.9mm × 5.0mm. The energy and intensity of the ¹²C beam were 290MeV/u and 10⁸ -10⁹ particle per second (pps). This beam condition is similar to the actual treatment condition in HIMAC. Carbon ions entered to a water phantom and all of the primary carbon ions were stopped in the water. The OpenPET detector was positioned 30cm apart from the backside of the water phantom at an angle of 30 degree. A coincidence detector was positioned at the opposite side of the water phantom. As a result, the sufficient crystal identification performance was achieved with slight deterioration of the position histograms.