title: Sensitivity of a helical diode array dosimeter to Volumetric Modulated Arc Therapy delivery errors.
abstract: OBJECTIVE
  To study the sensitivity of an ArcCHECK dosimeter in detecting delivery errors during the delivery of Volumetric Modulated Arc Therapy (VMAT).
  
  
  METHODS
  Three types of errors in Multi Leaf Collimator (MLC) position and dose delivery were simulated separately in the delivery of five prostate and five head and neck (H&N) VMAT plans: (i) Gantry independent: a systematic shift in MLC position and variation in output to the whole arc; (ii) Gantry dependent: sag in MLC position and output variation as a function of gantry angle; (iii) Control point specific MLC and output errors introduced to only a specific number of Control Points (CP). The difference in local and global gamma (γ) pass rate between the no-error and error-simulated measurements with 2%/2 mm and 3%/3 mm tolerances was calculated to assess the sensitivity of ArcCHECK. The clinical impact of these errors was also calculated.
  
  
  RESULTS
  ArcCHECK was able to detect a minimum 3 mm MLC error and 3% output error for Gantry independent errors using either local or global gamma with 2%/2 mm tolerance. For the Gantry dependent error scenario a minimum 3 mm MLC error and 3% dose error was identifiable by ArcCHECK using either global or local gamma with 2%/2 mm tolerance. In errors introduced to specific CPs a MLC error of 10 mm and dose error of 100% introduced to 4CPs were detected by ArcCHECK.
  
  
  CONCLUSIONS
  ArcCHECK used with either local or global gamma analysis and 2%/2 mm criteria can be confidently used in the clinic to detect errors above the stated error values.
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia. Electronic address: Sankar.Arumugam@sswahs.nsw.gov.au.
authors.forename: Sankar
authors.initials: S
authors.lastname: Arumugam
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia.
authors.forename: Aitang
authors.initials: A
authors.lastname: Xing
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia.
authors.forename: Tony
authors.initials: T
authors.lastname: Young
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; South West Clinical School, University of New South Wales, Sydney, NSW, Australia; Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia.
authors.forename: Lois
authors.initials: L
authors.lastname: Holloway
mesh_terms: D055615:Electrical Equipment and Supplies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D008297:Male; D019300:Medical Errors; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*
keywords: Delivery error; Helical diode array detector; VMAT