title: Development of a four-dimensional Monte Carlo dose calculation system for real-time tumor-tracking irradiation with a gimbaled X-ray head.
abstract: OBJECTIVE
  To develop a four-dimensional (4D) dose calculation system for real-time tumor tracking (RTTT) irradiation by the Vero4DRT.
  
  
  METHODS
  First, a 6-MV photon beam delivered by the Vero4DRT was simulated using EGSnrc. A moving phantom position was directly measured by a laser displacement gauge. The pan and tilt angles, monitor units, and the indexing time indicating the phantom position were also extracted from a log file. Next, phase space data at any angle were created from both the log file and particle data under the dynamic multileaf collimator. Irradiation both with and without RTTT, with the phantom moving, were simulated using several treatment field sizes. Each was compared with the corresponding measurement using films. Finally, dose calculation for each computed tomography dataset of 10 respiratory phases with the X-ray head rotated was performed to simulate the RTTT irradiation (4D plan) for lung, liver, and pancreatic cancer patients. Dose-volume histograms of the 4D plan were compared with those calculated on the single reference respiratory phase without the gimbal rotation [three-dimensional (3D) plan].
  
  
  RESULTS
  Differences between the simulated and measured doses were less than 3% for RTTT irradiation in most areas, except the high-dose gradient. For clinical cases, the target coverage in 4D plans was almost identical to that of the 3D plans. However, the doses to organs at risk in the 4D plans varied at intermediate- and low-dose levels.
  
  
  CONCLUSIONS
  Our proposed system has acceptable accuracy for RTTT irradiation in the Vero4DRT and is capable of simulating clinical RTTT plans.
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan. Electronic address: y.ishi@kuhp.kyoto-u.ac.jp.
authors.forename: Yoshitomo
authors.initials: Y
authors.lastname: Ishihara
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Miyabe
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Mukumoto
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Matsuo
authors.affiliation: Department of Radiological Technology, Faculty of Medical Science, Kyoto College of Medical Science, Nantan 622-0041, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Sawada
authors.affiliation: Department of Radiation Oncology, Kobe City Medical Center General Hospital, Kobe 650-0047, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Kokubo
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizowaki
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003198:Computer Simulation; D005260:Female; D056973:Four-Dimensional Computed Tomography / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008113:Liver Neoplasms / Q000532:radiotherapy / Q000601:surgery; D008175:Lung Neoplasms / Q000532:radiotherapy / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009010:Monte Carlo Method; D010190:Pancreatic Neoplasms / Q000532:radiotherapy / Q000601:surgery; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods*; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods; D012119:Respiration; D012984:Software
keywords: 4D dose calculation; IMRT; Monte Carlo; Real-time tumor-tracking irradiation; SBRT