title: Towards integration of PET/MR hybrid imaging into radiation therapy treatment planning.
abstract: OBJECTIVE
  Multimodality imaging has become an important adjunct of state-of-the-art radiation therapy (RT) treatment planning. Recently, simultaneous PET/MR hybrid imaging has become clinically available and may also contribute to target volume delineation and biological individualization in RT planning. For integration of PET/MR hybrid imaging into RT treatment planning, compatible dedicated RT devices are required for accurate patient positioning. In this study, prototype RT positioning devices intended for PET/MR hybrid imaging are introduced and tested toward PET/MR compatibility and image quality.
  
  
  METHODS
  A prototype flat RT table overlay and two radiofrequency (RF) coil holders that each fix one flexible body matrix RF coil for RT head/neck imaging have been evaluated within this study. MR image quality with the RT head setup was compared to the actual PET/MR setup with a dedicated head RF coil. PET photon attenuation and CT-based attenuation correction (AC) of the hardware components has been quantitatively evaluated by phantom scans. Clinical application of the new RT setup in PET/MR imaging was evaluated in anin vivo study.
  
  
  RESULTS
  The RT table overlay and RF coil holders are fully PET/MR compatible. MR phantom and volunteer imaging with the RT head setup revealed high image quality, comparable to images acquired with the dedicated PET/MR head RF coil, albeit with 25% reduced SNR. Repositioning accuracy of the RF coil holders was below 1 mm. PET photon attenuation of the RT table overlay was calculated to be 3.8% and 13.8% for the RF coil holders. With CT-based AC of the devices, the underestimation error was reduced to 0.6% and 0.8%, respectively. Comparable results were found within the patient study.
  
  
  CONCLUSIONS
  The newly designed RT devices for hybrid PET/MR imaging are PET and MR compatible. The mechanically rigid design and the reproducible positioning allow for straightforward CT-based AC. The systematic evaluation within this study provides the technical basis for the clinical integration of PET/MR hybrid imaging into RT treatment planning.
authors.affiliation: Institute of Medical Physics, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen 91052, Germany.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Paulus
authors.affiliation: Section for Biomedical Physics, University Hospital for Radiation Oncology, Eberhard Karls University Tübingen, Tübingen 72076, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Thorwath
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard Karls University Tübingen, Tübingen 72076, Germany; Laboratory for Preclinical Imaging and Imaging Technology of the Werner Siemens-Foundation, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University Tübingen, Tübingen 72076, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Schmidt
authors.affiliation: Institute of Medical Physics, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen 91052, Germany; Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen 45141, Germany; and High Field and Hybrid MR-Imaging, University Hospital Essen, Essen 45147, Germany.
authors.forename: Harald H
authors.initials: HH
authors.lastname: Quick
mesh_terms: D000328:Adult; D000368:Aged; D004867:Equipment Design; D006257:Head / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods; D008297:Male; D064847:Multimodal Imaging / Q000295:instrumentation* / Q000379:methods; D009333:Neck / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D056888:Patient Positioning / Q000295:instrumentation*; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation* / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation* / Q000379:methods