title: In-beam PET imaging for on-line adaptive proton therapy: an initial phantom study.
abstract: We developed and investigated a positron emission tomography (PET) system for use with on-line (both in-beam and intra-fraction) image-guided adaptive proton therapy applications. The PET has dual rotating depth-of-interaction measurable detector panels by using solid-state photomultiplier (SSPM) arrays and LYSO scintillators. It has a 44 mm diameter trans-axial and 30 mm axial field-of-view (FOV). A 38 mm diameter polymethyl methacrylate phantom was placed inside the FOV. Both PET and phantom axes were aligned with a collimated 179.2 MeV beam. Each beam delivered ∼50 spills (0.5 s spill and 1.5 s inter-spill time, 3.8 Gy at Bragg peak). Data from each beam were acquired with detectors at a given angle. Nine datasets for nine beams with detectors at nine different angles over 180° were acquired for full-tomographic imaging. Each dataset included data both during and 5 min after irradiations. The positron activity-range was measured from the PET image reconstructed from all nine datasets and compared to the results from simulated images. A (22)Na disc-source was also imaged after each beam to monitor the PET system's performance. PET performed well except for slight shifts of energy photo-peak positions (<1%) after each beam, due mainly to the neutron exposure of SSPM that increased the dark-count noise. This minor effect was corrected offline with a shifting 350-650 keV energy window for each dataset. The results show a fast converging of activity-ranges measured by the prototype PET with high sensitivity and uniform resolution. Sub-mm activity-ranges were achieved with minimal 6 s acquisition time and three spill irradiations. These results indicate the feasibility of PET for intra-fraction beam-range verification. Further studies are needed to develop and apply a novel clinical PET system for on-line image-guided adaptive proton therapy.
authors.affiliation: Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Shao
authors.forename: Xishan
authors.initials: X
authors.lastname: Sun
authors.forename: Kai
authors.initials: K
authors.lastname: Lou
authors.forename: Xiaorong R
authors.initials: XR
authors.lastname: Zhu
authors.forename: Dragon
authors.initials: D
authors.lastname: Mirkovic
authors.forename: Falk
authors.initials: F
authors.lastname: Poenisch
authors.forename: David
authors.initials: D
authors.lastname: Grosshans
mesh_terms: D005240:Feasibility Studies; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D061766:Proton Therapy / Q000295:instrumentation*; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation*