title: Volumetric modulated arc therapy for delivery of prostate radiotherapy: comparison with intensity-modulated radiotherapy and three-dimensional conformal radiotherapy.
abstract: OBJECTIVE
  Volumetric modulated arc therapy (VMAT) is a novel form of intensity-modulated radiotherapy (IMRT) optimization that allows the radiation dose to be delivered in a single gantry rotation of up to 360 degrees , using either a constant dose rate (cdr-VMAT) or variable dose rate (vdr-VMAT) during rotation. The goal of this study was to compare VMAT prostate RT plans with three-dimensional conformal RT (3D-CRT) and IMRT plans.
  
  
  METHODS
  The 3D-CRT, five-field IMRT, cdr-VMAT, and vdr-VMAT RT plans were created for 10 computed tomography data sets from patients undergoing RT for prostate cancer. The parameters evaluated included the doses to organs at risk, equivalent uniform doses, dose homogeneity and conformality, and monitor units required for delivery of a 2-Gy fraction.
  
  
  RESULTS
  The IMRT and both VMAT techniques resulted in lower doses to normal critical structures than 3D-CRT plans for nearly all dosimetric endpoints analyzed. The lowest doses to organs at risk and most favorable equivalent uniform doses were achieved with vdr-VMAT, which was significantly better than IMRT for the rectal and femoral head dosimetric endpoints (p < 0.05) and significantly better than cdr-VMAT for most bladder and rectal endpoints (p < 0.05). The vdr-VMAT and cdr-VMAT plans required fewer monitor units than did the IMRT plans (relative reduction of 42% and 38%, respectively; p = 0.005) but more than for the 3D-CRT plans (p = 0.005).
  
  
  CONCLUSIONS
  The IMRT and VMAT techniques achieved highly conformal treatment plans. The vdr-VMAT technique resulted in more favorable dose distributions than the IMRT or cdr-VMAT techniques, and reduced the monitor units required compared with IMRT.
authors.affiliation: Radiation Oncology Program, British Columbia Cancer Agency, Vancouver, BC, Canada. dpalma@bccancer.bc.ca
authors.forename: David
authors.initials: D
authors.lastname: Palma
authors.forename: Emily
authors.initials: E
authors.lastname: Vollans
authors.forename: Kerry
authors.initials: K
authors.lastname: James
authors.forename: Sandy
authors.initials: S
authors.lastname: Nakano
authors.forename: Vitali
authors.initials: V
authors.lastname: Moiseenko
authors.forename: Richard
authors.initials: R
authors.lastname: Shaffer
authors.forename: Michael
authors.initials: M
authors.lastname: McKenzie
authors.forename: James
authors.initials: J
authors.lastname: Morris
authors.forename: Karl
authors.initials: K
authors.lastname: Otto
mesh_terms: D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D016896:Treatment Outcome