title: Evaluation of MLC performance in VMAT and dynamic IMRT by log file analysis.
abstract: OBJECTIVE
  This multi-institution study assessed the positioning accuracy of multileaf collimators (MLC) by analyzing log files. It determined the main machine parameters that affect MLC positioning errors for pre-TrueBeam (Clinac) and TrueBeam linacs.
  
  
  METHODS
  Around 30,000 dIMRT and VMAT log files belonging to 6 linacs from 4 different centers were analyzed. An in-house software was used to calculate 95th percentile and RMS error values and their correlation with certain parameters such as maximum leaf speed, mean leaf speed and gantry angle. The effect of MLC communication delay on error statistics was assessed in Clinac linacs. To that end MLC positioning error statistics were calculated with and without the delay effect.
  
  
  RESULTS
  For dIMRT treatments in Clinac linacs the mean leaf RMS error was 0.306mm with and 0.030mm without the delay effect. Leaf RMS error was closely linked to maximum and mean leaf speeds, but without the delay effect that link was weaker. No trend was observed between bank RMS error and gantry angle. Without the delay effect larger bank RMS errors were obtained for gantry angles with leaf movements against gravity. For VMAT treatments in TrueBeam linacs the mean leaf RMS error was 0.038mm. A link was also observed between leaf RMS error and maximum and mean leaf speeds.
  
  
  CONCLUSIONS
  TrueBeam MLC positioning errors are substantially lower than those of Clinac linacs. In Clinac machines the analysis of dynalogs without the delay effect allows us to study the influence of factors that are masked by the delay effect.
authors.affiliation: Medical Physics Department, OSI Araba, Hospital Universitario Araba, Cl. Jose Atxotegi s/n, Vitoria-Gasteiz, Araba, Spain. Electronic address: jose.olasolo@gmail.com.
authors.forename: José
authors.initials: J
authors.lastname: Olasolo-Alonso
authors.affiliation: Medical Physics Department, Centro de Investigación Biomédica de La Rioja, Cl. Piqueras 98, Logroño, La Rioja, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Vázquez-Galiñanes
authors.affiliation: Medical Physics Department, Complejo Hospitalario de Navarra, Cl. Irunlarrea 3, Pamplona, Navarra, Spain.
authors.forename: Santiago
authors.initials: S
authors.lastname: Pellejero-Pellejero
authors.affiliation: Medical Physics Department, Hospital Universitario de Cruces, Plz. Cruces, Barakaldo, Vizcaya, Spain.
authors.forename: José Fernando
authors.initials: JF
authors.lastname: Pérez-Azorín
mesh_terms: D006801:Humans; D010315:Particle Accelerators; D056888:Patient Positioning; D011786:Quality Control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D012984:Software
keywords: Dynalog; IMRT; Trajectory log file; VMAT