title: Clinical application of in-room positron emission tomography for in vivo treatment monitoring in proton radiation therapy.
abstract: OBJECTIVE
  The purpose of this study is to evaluate the potential of using in-room positron emission tomography (PET) for treatment verification in proton therapy and for deriving suitable PET scan times.
  
  
  METHODS
  Nine patients undergoing passive scattering proton therapy underwent scanning immediately after treatment with an in-room PET scanner. The scanner was positioned next to the treatment head after treatment. The Monte Carlo (MC) method was used to reproduce PET activities for each patient. To assess the proton beam range uncertainty, we designed a novel concept in which the measured PET activity surface distal to the target at the end of range was compared with MC predictions. The repositioning of patients for the PET scan took, on average, approximately 2 minutes. The PET images were reconstructed considering varying scan times to test the scan time dependency of the method.
  
  
  RESULTS
  The measured PET images show overall good spatial correlations with MC predictions. Some discrepancies could be attributed to uncertainties in the local elemental composition and biological washout. For 8 patients treated with a single field, the average range differences between PET measurements and computed tomography (CT) image-based MC results were <5 mm (<3 mm for 6 of 8 patients) and root-mean-square deviations were 4 to 11 mm with PET-CT image co-registration errors of approximately 2 mm. Our results also show that a short-length PET scan of 5 minutes can yield results similar to those of a 20-minute PET scan.
  
  
  CONCLUSIONS
  Our first clinical trials in 9 patients using an in-room PET system demonstrated its potential for in vivo treatment monitoring in proton therapy. For a quantitative range prediction with arbitrary shape of target volume, we suggest using the distal PET activity surface.
authors: Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
authors: Chul Hee
authors: CH
authors: Min
authors: Xuping
authors: X
authors: Zhu
authors: Brian A
authors: BA
authors: Winey
authors: Kira
authors: K
authors: Grogg
authors: Mauro
authors: M
authors: Testa
authors: Georges
authors: G
authors: El Fakhri
authors: Thomas R
authors: TR
authors: Bortfeld
authors: Harald
authors: H
authors: Paganetti
authors: Helen A
authors: HA
authors: Shih
mesh_terms: D000328:Adult; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D009010:Monte Carlo Method; D056888:Patient Positioning / Q000379:methods; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D012542:Scattering, Radiation; D013997:Time Factors; D055815:Young Adult
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