title: Commissioning and quality assurance of RapidArc radiotherapy delivery system.
abstract: OBJECTIVE
  The Varian RapidArc is a system for intensity-modulated radiotherapy (IMRT) treatment planning and delivery. RapidArc incorporates capabilities such as variable dose-rate, variable gantry speed, and accurate and fast dynamic multileaf collimators (DMLC), to optimize dose conformality, delivery efficiency, accuracy and reliability. We developed RapidArc system commissioning and quality assurance (QA) procedures.
  
  
  METHODS
  Tests have been designed that evaluate RapidArc performance in a stepwise manner. First, the accuracy of DMLC position during gantry rotation is examined. Second, the ability to vary and control the dose-rate and gantry speed is evaluated. Third, the combined use of variable DMLC speed and dose-rate is studied.
  
  
  RESULTS
  Adapting the picket fence test for RapidArc, we compared the patterns obtained with stationary gantry and in RapidArc mode, and showed that the effect of gantry rotation on leaf accuracy was minimal (< or =0.2 mm). We then combine different dose-rates (111-600 MU/min), gantry speeds (5.5-4.3 degrees /s), and gantry range (Deltatheta = 90-12.9 degrees ) to give the same dose to seven parts of a film. When normalized to a corresponding open field (to account for flatness and asymmetry), the dose of the seven portions show good agreement, with a mean deviation of 0.7%. In assessing DMLC speed (0.46, 0.92, 1.84, and 2.76 cm/s) during RapidArc, the analysis of designed radiation pattern indicates good agreement, with a mean deviation of 0.4%.
  
  
  CONCLUSIONS
  The results of these tests provide strong evidence that DMLC movement, variable dose-rates and gantry speeds can be precisely controlled during RapidArc.
authors.affiliation: Varian Medical Systems, Palo Alto, CA, USA. lingc@mskcc.org
authors.forename: C Clifton
authors.initials: CC
authors.lastname: Ling
authors.forename: Pengpeng
authors.initials: P
authors.lastname: Zhang
authors.forename: Yves
authors.initials: Y
authors.lastname: Archambault
authors.forename: Jiri
authors.initials: J
authors.lastname: Bocanek
authors.forename: Grace
authors.initials: G
authors.lastname: Tang
authors.forename: Thomas
authors.initials: T
authors.lastname: Losasso
mesh_terms: D002138:Calibration; D005373:Film Dosimetry; D010315:Particle Accelerators / Q000295:instrumentation* / Q000592:standards; D011786:Quality Control; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D012399:Rotation