title: Prediction error and required internal margin provided for irregular respiratory movements: a phantom study.
abstract: OBJECTIVE
  To estimate the prediction error and required internal margin provided for irregular respiratory movements.
  
  
  METHODS
  Twenty-eight patterns of irregular movement were prepared using a moving phantom. For irregular cycle movement, a cycle of 2.0-5.0 s was inserted into the baseline movement data (3.5-s cycle, 6-mm amplitude) every four cycles. In addition, a cycle of 2.5-4.5 s was further inserted into one of the irregular data points every four cycles to produce more complicated irregularity. For irregular amplitude movement, an amplitude of 3.0-9.0 mm was inserted into the baseline respiratory movement data. In addition, an amplitude of 4.0-8.0 mm was further inserted into one of the irregular data points every four cycles to produce more complicated irregularity. Images of the moving target were acquired using a real-time position management (RPM) and four-dimensional CT (4DCT) system. The displacement from the baseline image and required margin to compensate for irregular movement were calculated.
  
  
  RESULTS
  Amplitude irregularity tended to lose stable placement and need larger margins to compensate for the reduction of image reproducibility than cycle irregularity. There was a large displacement and required margin when the target moved with more complicated irregular amplitude.
  
  
  CONCLUSIONS
  The RPM and 4DCT system has a risk of prediction error, which may result from the complicated amplitude irregularity of respiratory movement.
authors: Proton Medical Research Center, University of Tsukuba, 1-1-1, Tennoudai, Tsukuba, 305-8575, Japan, fukumitsun@yahoo.co.jp.
authors: Nobuyoshi
authors: N
authors: Fukumitsu
authors: Haruko
authors: H
authors: Numajiri
authors: Kayoko
authors: K
authors: Ohnishi
authors: Masashi
authors: M
authors: Mizumoto
authors: Teruhito
authors: T
authors: Aihara
authors: Hitoshi
authors: H
authors: Ishikawa
authors: Toshiyuki
authors: T
authors: Okumura
authors: Koji
authors: K
authors: Tsuboi
authors: Toshiyuki
authors: T
authors: Terunuma
authors: Takeji
authors: T
authors: Sakae
authors: Hideyuki
authors: H
authors: Sakurai
mesh_terms: D016477:Artifacts; D056973:Four-Dimensional Computed Tomography; D007091:Image Processing, Computer-Assisted; D008954:Models, Biological; D009068:Movement; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012119:Respiration