title: Prostatic displacement during extreme hypofractionated radiotherapy using volumetric modulated arc therapy (VMAT).
abstract: BACKGROUND
  To determine prostate displacement during extreme hypofractionated volume modulated arc radiotherapy (VMAT) using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers.
  
  
  METHODS
  A total of 150 image pairs were obtained from 30 patients who underwent extreme hypofractionated radiotherapy to a dose of 40 Gy in five fractions on standard linear accelerators. Position verification was obtained with orthogonal x-rays before and after treatment and were used to determine intra-fraction prostate displacement.
  
  
  RESULTS
  The mean prostate displacements were 0.03 ± 1.23 mm (1SD), 0.18 ± 1.55 mm, and 0.37 ± 1.95 mm in the left-right, superior-inferior, and anterior-posterior directions, respectively. The mean 3D displacement was 2.32 ± 1.55 mm. Only 6 (4%) fractions had a 3D displacement of >5 mm. The average time of treatment delivery for a given fraction was 195 ± 59 seconds.
  
  
  CONCLUSIONS
  The mean intra-fraction prostate displacement during a course of extreme hypofractionated radiotherapy delivered via VMAT, continues to be small. Clinical margins typically used in a similar fixed-angle IMRT treatment are adequate. The use of VMAT in further extreme hypofractionation may limit prostatic motion uncertainties that would be otherwise be associated with longer treatment times.
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Canada. adam.gladwich@sunnybrook.ca.
authors.forename: Adam
authors.initials: A
authors.lastname: Gladwish
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Canada. geordi.pang@sunnybrook.ca.|Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. geordi.pang@sunnybrook.ca.
authors.forename: Geordi
authors.initials: G
authors.lastname: Pang
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Canada. patrick.cheung@sunnybrook.ca.|Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. patrick.cheung@sunnybrook.ca.
authors.forename: Patrick
authors.initials: P
authors.lastname: Cheung
authors.affiliation: Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. laura.dalimonte@sunnybrook.ca.
authors.forename: Laura
authors.initials: L
authors.lastname: D'Alimonte
authors.affiliation: Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. andrea.deabreu@sunnybrook.ca.
authors.forename: Andrea
authors.initials: A
authors.lastname: Deabreu
authors.affiliation: Department of Radiation Oncology, University of Toronto, Toronto, Canada. andrew.loblaw@sunnybrook.ca.|Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. andrew.loblaw@sunnybrook.ca.|Department of Radiation Oncology, Sunnybrook Health Sciences Centre, 2075 Bayview Ave, Rm T2-103, Toronto, Ontario, M4N 3 M5, Canada. andrew.loblaw@sunnybrook.ca.
authors.forename: Andrew
authors.initials: A
authors.lastname: Loblaw
mesh_terms: D016477:Artifacts; D019583:Dose Fractionation, Radiation; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D009038:Motion; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D016032:Randomized Controlled Trials as Topic