title: Evaluation of inter- and intrafraction organ motion during intensity modulated radiation therapy (IMRT) for localized prostate cancer measured by a newly developed on-board image-guided system.
abstract: OBJECTIVE
  To investigate prostatic organ motion at both setup and intrafraction using an onboard image-guided system. An intrafraction field-based repositioning method also was evaluated.
  
  
  METHODS
  A dual fluoroscopy with amorphous-silicon flat panel (DFFP) system was used for the three-dimensional registration of implanted markers in the prostate of eight organ-confined cancer patients planned for treatment with intensity modulated radiation therapy (IMRT). Day-to-day motion errors were quantified and intrafraction displacements of more than +/-1 mm were corrected.
  
  
  RESULTS
  Among 214 fractions and 565 system views, day-to-day mean magnitude of marker discrepancy +/- standard deviation (SD) was 1.76 +/- 1.4 mm, 3.14 +/- 1.6 mm, and 3.78 +/- 2.4 mm in the right-left, cranial-caudal, and anterior-posterior directions, respectively. The intrafractional mean magnitude +/- SD of marker displacement was 0.45 +/- 0.7 mm, 1.08 +/- 1.38 mm and 1.45 +/- 1.70 mm in the right-left, cranial-caudal, and anterior-posterior directions, respectively. Intrafraction corrected sessions (84/214) showed a median (range) of motion of 0.1 mm (-1.2 to 0.7 mm), -0.2 mm (-2.1 to 1.1 mm), and -0.2 mm (-1.7 to 2.0 mm) in the right-left, cranial-caudal, and anterior-posterior directions, respectively.
  
  
  CONCLUSIONS
  Motion uncertainty can be considerably decreased with daily use of the DFFP system. Reduced intrafraction organ motion clearly endorsed the value of the repositioning approach, allowing a safer dose escalation protocol.
authors.affiliation: Department of Radiation Oncology, Tohoku University Graduate School of Medicine, Japan.
authors.forename: Keith R
authors.initials: KR
authors.lastname: Britton
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Takai
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Mitsuya
authors.forename: Kenji
authors.initials: K
authors.lastname: Nemoto
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Shogo
authors.initials: S
authors.lastname: Yamada
mesh_terms: D005471:Fluoroscopy; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008297:Male; D009068:Movement; D011467:Prostate; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*