title: Volumetric modulated Arc therapy and conventional intensity-modulated radiotherapy for simultaneous maximal intraprostatic boost: a planning comparison study.
abstract: OBJECTIVE
  Volumetric modulated arc therapy (VMAT) is a novel extension of intensity-modulated radiotherapy (IMRT) where an optimised three-dimensional dose distribution may be delivered in a single gantry rotation. This optimisation algorithm is the predecessor to Varian's RapidArc. The aim of this study was to compare the ability of conventional static nine-field IMRT (cIMRT) and VMAT to boost as much of the clinical target volume (CTV) as possible to 88.8Gy without exceeding organ at risk (OAR) dose-volume constraints.
  
  
  METHODS
  Optimal cIMRT and VMAT radiotherapy plans were produced for 10 patients with localised prostate cancer using common planning objectives: (1) Treat >or=98% of the planning target volume (PTV) to >or=95% of the prescription dose (74Gy in 37 fractions); (2) keep OAR doses within predefined limits; (3) treat as much of prostate CTV (minus urethra) as possible to >or=120% of prescription dose (=88.8Gy); (4) keep within maximum dose limits in and out of target volumes; (5) conformality index (volume of 95% isodose/volume of PTV)<or=1.2.
  
  
  RESULTS
  VMAT and cIMRT boosted an average of 68.8 and 63.5% of the CTV to >or=120% of the prescription dose (P=0.002). All dose constraints were kept within predefined limits. VMAT and cIMRT required an average of 949 and 1819 monitor units and 3.7 and 9.6min, respectively, to deliver a single radiation fraction.
  
  
  CONCLUSIONS
  VMAT is able to boost more of the CTV to >or=120% than cIMRT without contravening OAR dose constraints, and uses 48% fewer monitor units. Treatment times were 61% less than with cIMRT.
authors.affiliation: British Columbia Cancer Agency, 600 West 10th Avenue, Vancouver, British Columbia, Canada. rickyshaffer@yahoo.co.uk
authors.forename: R
authors.initials: R
authors.lastname: Shaffer
authors.forename: W J
authors.initials: WJ
authors.lastname: Morris
authors.forename: V
authors.initials: V
authors.lastname: Moiseenko
authors.forename: M
authors.initials: M
authors.lastname: Welsh
authors.forename: C
authors.initials: C
authors.lastname: Crumley
authors.forename: S
authors.initials: S
authors.lastname: Nakano
authors.forename: M
authors.initials: M
authors.lastname: Schmuland
authors.forename: T
authors.initials: T
authors.lastname: Pickles
authors.forename: K
authors.initials: K
authors.lastname: Otto
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D016555:Matched-Pair Analysis; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D047368:Tumor Burden