Sub-scanner characterizing for a dedicated head-and-neck cancer PET

1389 Objectives: The complex anatomical structure and vital physiological role of the tumor-involved region requires that the treatment goal of head-and-neck cancers (HNC) is not only to improve survival outcomes but also to preserve organ functions. Though whole-body PET has been widely used for HNC early diagnosis, recurrence prediction and radiotherapy, its low sensitivity and poor spatial and contrast resolution limit its management to HNC. We are developing a dedicated HNC PET scanner at University of Illinois at Urban Champaign. For the sake of a high sensitivity, the scanner will use a spacing-adjustable two-panel geometry. Small crystal size and dual-ended readout will also be utilized, which have the potential for providing a high-resolution neck imaging. We have built a detector module, and the next step is to scale it up to a sub-scanner. The goal of this presentation is to implement and characterize the sub-scanner. Methods: The detector module was based on a 6[asterisk]6 array of 1[asterisk]1[asterisk]20 mm3 LYSO. Dual-ended readout was achieved by placing two Hamamatsu 3050AE-08 SiPM array on both ends of the LYSO block. Since each SiPM channel had a 3[asterisk]3 mm2 sensitive area, a 2-mm light guide was used between the SiPM and LYSO block for crystal identification. SiPM output signals were digitized by PETsys TOFPET2 ASIC and acquired by PETsys SiPM Readout System. To measure the DOI resolution, a 30 uCi Na-22 source was used, whose active diameter was 0.25 mm. Coincidence events between the LYSO block and another single 3[asterisk]3[asterisk]5 mm3LYSO were selected to constrain the photon incident position along the depth direction. The distance from the source to the single LYSO was 60 mm, while that to the LYSO block was 20 mm, which gave a 1 mm intrinsic DOI resolution. 10 datasets, i.e., depth at 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 mm of the LYSO block were collected and each set acquired data for 600 s. Coincidence time resolution and energy resolution at different depths were also analyzed. Results: Given the setup, all the 6[asterisk]6 pixels in the LYSO block could be distinguished. The average CTR between the detector module and the single LYSO over the 10 datasets was 550.7+-134.6 ps, and the average energy resolution was 19.85%+-2.23% at 511 keV. By carefully controlling the surface roughness of each pixel in the LYSO block and selecting the reflector material, an excellent DOI resolution of 1.64+-0.16 mm was achieved. We had a design of a sub-scanner by scaling up the detector module. The sub-scanner will consist two panels and each panel have a sensitive area of 51.8[asterisk]58.7[asterisk]20 mm3. Readout electronics will be placed on the one side of LYSO to save the space between the two panels. We will also implement a cooling system to provide a low and stable temperature environment. Conclusions: We are developing a dedicated head-and-neck cancer PET scanner at UIUC. A high-resolution dual-ended readout detector module has been designed and characterized, which showed good DOI resolution, time resolution and energy resolution. We will scale the detector module up to a sub-scanner and characterize it in the presentation. Funding support: We acknowledge NIH R01-EB028091 and Cancer Scholars for Translational and Applied Research Program(C[asterisk]STAR) which is jointly funded by the Carle Foundation Hospital and the University of Illinois.