title: Impact of Real-Time Image Gating on Spot Scanning Proton Therapy for Lung Tumors: A Simulation Study.
abstract: To investigate the effectiveness of real-time-image gated proton beam therapy for lung tumors and to establish a suitable size for the gating window (GW).
  
  
  
  A proton beam gated by a fiducial marker entering a preassigned GW (as monitored by 2 fluoroscopy units) was used with 7 lung cancer patients. Seven treatment plans were generated: real-time-image gated proton beam therapy with GW sizes of ±1, 2, 3, 4, 5, and 8 mm and free-breathing proton therapy. The prescribed dose was 70 Gy (relative biological effectiveness)/10 fractions to 99% of the target. Each of the 3-dimensional marker positions in the time series was associated with the appropriate 4-dimensional computed tomography phase. The 4-dimensional dose calculations were performed. The dose distribution in each respiratory phase was deformed into the end-exhale computed tomography image. The D99 and D5 to D95 of the clinical target volume scaled by the prescribed dose with criteria of D99 >95% and D5 to D95 <5%, V20 for the normal lung, and treatment times were evaluated.
  
  
  
  Gating windows ≤ ±2 mm fulfilled the CTV criteria for all patients (whereas the criteria were not always met for GWs ≥ ±3 mm) and gave an average reduction in V20 of more than 17.2% relative to free-breathing proton therapy (whereas GWs ≥ ±4 mm resulted in similar or increased V20). The average (maximum) irradiation times were 384 seconds (818 seconds) for the ±1-mm GW, but less than 226 seconds (292 seconds) for the ±2-mm GW. The maximum increased considerably at ±1-mm GW.
  
  
  
  Real-time-image gated proton beam therapy with a GW of ±2 mm was demonstrated to be suitable, providing good dose distribution without greatly extending treatment time.
authors.affiliation: Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kanehira
authors.affiliation: Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan; Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan; Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Japan. Electronic address: matsuura@med.hokudai.ac.jp.
authors.forename: Taeko
authors.initials: T
authors.lastname: Matsuura
authors.affiliation: Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan.
authors.forename: Seishin
authors.initials: S
authors.lastname: Takao
authors.affiliation: Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Matsuzaki
authors.affiliation: Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Fujii
authors.affiliation: Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Fujii
authors.affiliation: Department of Biostatistics, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Yoichi M
authors.initials: YM
authors.lastname: Ito
authors.affiliation: Department of Medical Physics, Hokkaido University Hospital, Sapporo, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Miyamoto
authors.affiliation: Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Inoue
authors.affiliation: Department of Radiation Oncology, Hokkaido University Hospital, Sapporo, Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Katoh
authors.affiliation: Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan; Department of Radiation Oncology, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Shimizu
authors.affiliation: Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan; Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Japan.
authors.forename: Kikuo
authors.initials: K
authors.lastname: Umegaki
authors.affiliation: Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan; Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D057918:Fiducial Markers; D056973:Four-Dimensional Computed Tomography / Q000379:methods; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D009068:Movement; D061766:Proton Therapy / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D000066908:Simulation Training / Q000379:methods; D013997:Time Factors