title: Intrafractional tracking accuracy in infrared marker-based hybrid dynamic tumour-tracking irradiation with a gimballed linac.
abstract: OBJECTIVE
  To verify the intrafractional tracking accuracy in infrared (IR) marker-based hybrid dynamic tumour tracking irradiation ("IR Tracking") with the Vero4DRT.
  
  
  METHODS
  The gimballed X-ray head tracks a moving target by predicting its future position from displacements of IR markers in real-time. Ten lung cancer patients who underwent IR Tracking were enrolled. The 95th percentiles of intrafractional mechanical (iEM(95)), prediction (iEP(95)), and overall targeting errors (iET(95)) were calculated from orthogonal fluoroscopy images acquired during tracking irradiation and from the synchronously acquired log files.
  
  
  RESULTS
  Averaged intrafractional errors were (left-right, cranio-caudal [CC], anterior-posterior [AP])=(0.1mm, 0.4mm, 0.1mm) for iEM(95), (1.2mm, 2.7mm, 2.1mm) for iEP(95), and (1.3mm, 2.4mm, 1.4mm) for iET(95). By correcting systematic prediction errors in the previous field, the iEP(95) was reduced significantly, by an average of 0.4mm in the CC (p<0.05) and by 0.3mm in the AP (p<0.01) directions.
  
  
  CONCLUSIONS
  Prediction errors were the primary cause of overall targeting errors, whereas mechanical errors were negligible. Furthermore, improvement of the prediction accuracy could be achieved by correcting systematic prediction errors in the previous field.
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Mukumoto
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan. Electronic address: m_nkmr@kuhp.kyoto-u.ac.jp.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yamada
authors.affiliation: Advanced Mechanical Systems Department, Mitsubishi Heavy Industries Ltd, Hiroshima, Japan.
authors.forename: Kunio
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Division of Radiation Oncology, Institute of Biomedical Research and Innovation, Kobe, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tanabe
authors.affiliation: Division of Clinical Radiology Service, Kyoto University Hospital, Japan.
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Yano
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Miyabe
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Nami
authors.initials: N
authors.lastname: Ueki
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Shuji
authors.initials: S
authors.lastname: Kaneko
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Matsuo
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizowaki
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan; Department of Radiological Technology, Faculty of Medical Science, Kyoto College of Medical Science, Nantan, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Sawada
authors.affiliation: Division of Radiation Oncology, Institute of Biomedical Research and Innovation, Kobe, Japan; Department of Radiation Oncology, Kobe City Medical Center General Hospital, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Kokubo
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University Graduate School of Medicine, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D057918:Fiducial Markers; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D007259:Infrared Rays; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009068:Movement; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods*
keywords: Dynamic tumour-tracking irradiation; Four-dimensional image-guided radiotherapy; Intra-fractional tracking accuracy; Respiratory motion; Vero4DRT