title: Twin machines validation for VMAT treatments using electronic portal-imaging device: a multicenter study.
abstract: OBJECTIVE
  To verify the accuracy of volumetric arc therapy (VMAT) using the RapidArc™ device when switching patients from one single linear accelerator (linac) to a paired energy and mechanics "twin" linac without reoptimization of the original treatment plan.
  
  
  METHODS
  Four centers using 8 linacs were involved in this study. Seventy-four patients previously treated with the 6MV photon RapidArc™ technique were selected for analysis, using 242 measurements. In each institution, all patients were planned on linac A, and their plans were verified both on linac A and on the twin linac B. Verifications were done using the amorphous silicium electronic portal imager (EPID) of the linacs and were analyzed with the EpiQa software (Epidos, Bratislavia, Slovakia). The gamma index formalism was used for validation with a double threshold of 3 % and 3 mm with a measurement resolution of 0.39 mm/pixel, and a smoothed resolution of approximately 2.5 mm.
  
  
  RESULTS
  The number of points passing the gamma criteria between the measured and computed doses was 94.79 ± 2.57 % for linac A and 94.61 ± 2.46 % for linac B. Concerning the smoothed measurement analysis, 98.67 ± 1.26 % and 98.59 ± 1.20 % points passing the threshold were obtained for linacs A and B, respectively. The difference between the 2 dose matrices acquired on the EPID was very small, with 99.92 ± 0.06 % of the points passing the criteria.
  
  
  CONCLUSIONS
  For linacs sharing the same mechanical and energy parameters, this study tends to indicate that patients may be safely switched from treatment with one linac to treatment with its twin linac using the same VMAT plan.
authors.affiliation: Département d'Oncologie Radiothérapie, Institut régional du Cancer de Montpellier (ICM), 208 rue des Apothicaires, F-34298, Montpellier, Cedex 5, France. pascal.fenoglietto@icm.unicancer.fr.
authors.forename: P
authors.initials: P
authors.lastname: Fenoglietto
authors.affiliation: Département d'Oncologie Radiothérapie, Institut de Cancérologie de la Loire (ICL), Saint Etienne, France. mustapha.khodri@icloire.fr.
authors.forename: M
authors.initials: M
authors.lastname: Khodri
authors.affiliation: Service de radiothérapie, Groupe ORLAM, Mâcon, France. nguyen.daniel@yahoo.fr.
authors.forename: D
authors.initials: D
authors.lastname: Nguyen
authors.affiliation: Service de radiothérapie, Groupe ORLAM, Villeurbanne, France. florentin.jp@gmail.com.
authors.forename: F
authors.initials: F
authors.lastname: Josserand-Pietri
authors.affiliation: Département d'Oncologie Radiothérapie, Institut régional du Cancer de Montpellier (ICM), 208 rue des Apothicaires, F-34298, Montpellier, Cedex 5, France. norbert.ailleres@icm.unicancer.fr.
authors.forename: N
authors.initials: N
authors.lastname: Aillères
mesh_terms: D000465:Algorithms; D002138:Calibration; D004581:Electronics; D005260:Female; D005602:France; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D009369:Neoplasms / Q000532:radiotherapy*; D016011:Normal Distribution; D010315:Particle Accelerators; D010386:Pelvic Neoplasms / Q000532:radiotherapy*; D011785:Quality Assurance, Health Care; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012984:Software