title: Volumetric modulated arc therapy: planning and evaluation for prostate cancer cases.
abstract: OBJECTIVE
  To develop an optimization method using volumetric modulated arc therapy (VMAT) and evaluate VMAT plans relative to the standard intensity-modulated radiotherapy (IMRT) approach in prostate cancer.
  
  
  METHODS
  A single gantry rotation was modeled using 177 equispaced beams. Multileaf collimator apertures and dose rates were optimized with respect to gantry angle subject to dose-volume-based objectives. Our VMAT implementation used conjugate gradient descent to optimize dose rate, and stochastic sampling to find optimal multileaf collimator leaf positions. A treatment planning study of 11 prostate cancer patients with a prescription dose of 86.4 Gy was performed to compare VMAT with a standard five-field IMRT approach. Plan evaluation statistics included the percentage of planning target volume (PTV) receiving 95% of prescribed dose (V95), dose to 95% of PTV (D95), mean PTV dose, tumor control probability, and dosimetric endpoints of normal organs, whereas monitor unit (MU) and delivery time were used to assess delivery efficiency.
  
  
  RESULTS
  Patient-averaged PTV V95, D95, mean dose, and tumor control probability in VMAT plans were 96%, 82.6 Gy, 88.5 Gy, and 0.920, respectively, vs. 97%, 84.0 Gy, 88.9 Gy, and 0.929 in IMRT plans. All critical structure dose requirements were met. The VMAT plans presented better rectal wall sparing, with a reduction of 1.5% in normal tissue complication probability. An advantage of VMAT plans was that the average number of MUs (290 MU) was less than for IMRT plans (642 MU).
  
  
  CONCLUSIONS
  The VMAT technique can reduce beam on time by up to 55% while maintaining dosimetric quality comparable to that of the standard IMRT approach.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA. zhangp@mskcc.org
authors.forename: Pengpeng
authors.initials: P
authors.lastname: Zhang
authors.forename: Laura
authors.initials: L
authors.lastname: Happersett
authors.forename: Margie
authors.initials: M
authors.lastname: Hunt
authors.forename: Andrew
authors.initials: A
authors.lastname: Jackson
authors.forename: Michael
authors.initials: M
authors.lastname: Zelefsky
authors.forename: Gig
authors.initials: G
authors.lastname: Mageras
mesh_terms: D000465:Algorithms; D002138:Calibration; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D012189:Retrospective Studies