title: Accuracy of real-time couch tracking during 3-dimensional conformal radiation therapy, intensity modulated radiation therapy, and volumetric modulated arc therapy for prostate cancer.
abstract: OBJECTIVE
  To evaluate the accuracy of real-time couch tracking for prostate cancer.
  
  
  METHODS
  Intrafractional motion trajectories of 15 prostate cancer patients were the basis for this phantom study; prostate motion had been monitored with the Calypso System. An industrial robot moved a phantom along these trajectories, motion was detected via an infrared camera system, and the robotic HexaPOD couch was used for real-time counter-steering. Residual phantom motion during real-time tracking was measured with the infrared camera system. Film dosimetry was performed during delivery of 3-dimensional conformal radiation therapy (3D-CRT), step-and-shoot intensity modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT).
  
  
  RESULTS
  Motion of the prostate was largest in the anterior-posterior direction, with systematic (∑) and random (σ) errors of 2.3 mm and 2.9 mm, respectively; the prostate was outside a threshold of 5 mm (3D vector) for 25.0%±19.8% of treatment time. Real-time tracking reduced prostate motion to ∑=0.01 mm and σ = 0.55 mm in the anterior-posterior direction; the prostate remained within a 1-mm and 5-mm threshold for 93.9%±4.6% and 99.7%±0.4% of the time, respectively. Without real-time tracking, pass rates based on a γ index of 2%/2 mm in film dosimetry ranged between 66% and 72% for 3D-CRT, IMRT, and VMAT, on average. Real-time tracking increased pass rates to minimum 98% on average for 3D-CRT, IMRT, and VMAT.
  
  
  CONCLUSIONS
  Real-time couch tracking resulted in submillimeter accuracy for prostate cancer, which transferred into high dosimetric accuracy independently of whether 3D-CRT, IMRT, or VMAT was used.
authors.affiliation: Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Juergen
authors.initials: J
authors.lastname: Wilbert
authors.forename: Kurt
authors.initials: K
authors.lastname: Baier
authors.forename: Christian
authors.initials: C
authors.lastname: Hermann
authors.forename: Michael
authors.initials: M
authors.lastname: Flentje
authors.forename: Matthias
authors.initials: M
authors.lastname: Guckenberger
mesh_terms: D006801:Humans; D008297:Male; D009068:Movement; D019047:Phantoms, Imaging; D011467:Prostate; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012371:Robotics / Q000295:instrumentation