title: Toward correcting drift in target position during radiotherapy via computer-controlled couch adjustments on a programmable Linac.
abstract: OBJECTIVE
  Real-time tracking of respiratory target motion during radiation therapy is technically challenging, owing to rapid and possibly irregular breathing variations. The authors report on a method to predict and correct respiration-averaged drift in target position by means of couch adjustments on an accelerator equipped with such capability.
  
  
  METHODS
  Dose delivery is broken up into a sequence of 10 s field segments, each followed by a couch adjustment based on analysis of breathing motion from an external monitor as a surrogate of internal target motion. Signal averaging over three respiratory cycles yields a baseline representing target drift. A Kalman filter predicts the baseline position 5 s in advance, for determination of the couch correction. The method's feasibility is tested with a motion phantom programmed according to previously recorded patient signals. Computed couch corrections are preprogrammed into a research mode of an accelerator capable of computer-controlled couch translations synchronized with the motion phantom. The method's performance is evaluated with five cases recorded during hypofractionated treatment and five from respiration-correlated CT simulation, using a root-mean-squared deviation (RMSD) of the baseline from the treatment planned position.
  
  
  RESULTS
  RMSD is reduced in all 10 cases, from a mean of 4.9 mm (range 2.7-9.4 mm) before correction to 1.7 mm (range 0.7-2.3 mm) after correction. Treatment time is increased ∼5% relative to that for no corrections.
  
  
  CONCLUSIONS
  This work illustrates the potential for reduction in baseline respiratory drift with periodic adjustments in couch position during treatment. Future treatment machine capabilities will enable the use of "on-the-fly" couch adjustments during treatment.
authors: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA.
authors: Joseph E
authors: JE
authors: McNamara
authors: Rajesh
authors: R
authors: Regmi
authors: D
authors: D
authors: Michael Lovelock
authors: Ellen D
authors: ED
authors: Yorke
authors: Karyn A
authors: KA
authors: Goodman
authors: Andreas
authors: A
authors: Rimner
authors: Hassan
authors: H
authors: Mostafavi
authors: Gig S
authors: GS
authors: Mageras
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D009068:Movement; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*
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