title: Analysis of inter-fraction setup errors and organ motion by daily kilovoltage cone beam computed tomography in intensity modulated radiotherapy of prostate cancer.
abstract: BACKGROUND
  Intensity-modulated radiotherapy (IMRT) enables a better conformality to the target while sparing the surrounding normal tissues and potentially allows to increase the dose to the target, if this is precisely and accurately determined. The goal of this work is to determine inter-fraction setup errors and prostate motion in IMRT for localized prostate cancer, guided by daily kilovoltage cone beam computed tomography (kVCBCT).
  
  
  METHODS
  Systematic and random components of the shifts were retrospectively evaluated by comparing two matching modalities (automatic bone and manual soft-tissue) between each of the 641 daily kVCBCTs (18 patients) and the planning kVCT. A simulated Adaptive Radiation Therapy (ART) protocol using the average of the first 5 kVCBCTs was tested by non-parametric bootstrapping procedure.
  
  
  RESULTS
  Shifts were < 1 mm in left-right (LR) and in supero-inferior (SI) direction. In antero-posterior (AP) direction systematic prostate motion (2.7 ± 0.7 mm) gave the major contribution to the variability of results; the averages of the absolute total shifts were significantly larger in anterior (6.3 ± 0.2 mm) than in posterior (3.9 mm ± 0.2 mm) direction. The ART protocol would reduce margins in LR, SI and anterior but not in posterior direction.
  
  
  CONCLUSIONS
  The online soft-tissue correction based on daily kVCBCT during IMRT of prostate cancer is fast and efficient. The large random movements of prostate respect to bony anatomy, especially in the AP direction, where anisotropic margins are needed, suggest that daily kVCBCT is at the present time preferable for high dose and high gradients IMRT prostate treatments.
authors.affiliation: Department of Physics, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy.
authors.forename: Marcella
authors.initials: M
authors.lastname: Palombarini
authors.forename: Stefano
authors.initials: S
authors.lastname: Mengoli
authors.forename: Paola
authors.initials: P
authors.lastname: Fantazzini
authors.forename: Cecilia
authors.initials: C
authors.lastname: Cadioli
authors.forename: Claudio
authors.initials: C
authors.lastname: Degli Esposti
authors.forename: Giovanni Piero
authors.initials: GP
authors.lastname: Frezza
mesh_terms: D000230:Adenocarcinoma / Q000532:radiotherapy*; D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D009038:Motion; D015588:Observer Variation; D009862:Online Systems; D058958:Organs at Risk; D010384:Pelvic Bones; D011467:Prostate; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D015641:Radiography, Interventional / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric