title: An external dosimetry audit programme to credential static and rotational IMRT delivery for clinical trials quality assurance.
abstract: OBJECTIVE
  External dosimetry audits give confidence in the safe and accurate delivery of radiotherapy. The RTTQA group have performed an on-site audit programme for trial recruiting centres, who have recently implemented static or rotational IMRT, and those with major changes to planning or delivery systems.
  
  
  METHODS
  Measurements of reference beam output were performed by the host centre, and by the auditor using independent equipment. Verification of clinical plans was performed using the ArcCheck helical diode array.
  
  
  RESULTS
  A total of 54 measurement sessions were performed between May 2014 and June 2016 at 28 UK institutions, reflecting the different combinations of planning and delivery systems used at each institution. Average ratio of measured output between auditor and host was 1.002±0.006. Average point dose agreement for clinical plans was -0.3±1.8%. Average (and 95% lower confidence intervals) of gamma pass rates at 2%/2mm, 3%/2mm and 3%/3mm respectively were: 92% (80%), 96% (90%) and 98% (94%). Moderately significant differences were seen between fixed gantry angle and rotational IMRT, and between combination of planning systems and linac manufacturer, but not between anatomical treatment site or beam energy.
  
  
  CONCLUSIONS
  An external audit programme has been implemented for universal and efficient credentialing of IMRT treatments in clinical trials. Good agreement was found between measured and expected doses, with few outliers, leading to a simple table of optimal and mandatory tolerances for approval of dosimetry audit results. Feedback was given to some centres leading to improved clinical practice.
authors.affiliation: Radiotherapy Trials QA Group (RTTQA), Mount Vernon Hospital, Northwood, UK. Electronic address: davideaton@nhs.net.
authors.forename: David J
authors.initials: DJ
authors.lastname: Eaton
authors.affiliation: RTTQA, Royal Marsden Hospital, Fulham Road, London, UK.
authors.forename: Justine
authors.initials: J
authors.lastname: Tyler
authors.affiliation: RTTQA, Royal Marsden Hospital, Fulham Road, London, UK.
authors.forename: Alex
authors.initials: A
authors.lastname: Backshall
authors.affiliation: RTTQA, Royal Marsden Hospital, Fulham Road, London, UK.
authors.forename: David
authors.initials: D
authors.lastname: Bernstein
authors.affiliation: RTTQA, Queen Elizabeth Hospital, Birmingham, UK.
authors.forename: Antony
authors.initials: A
authors.lastname: Carver
authors.affiliation: RTTQA, Royal Marsden Hospital, Fulham Road, London, UK.
authors.forename: Anne
authors.initials: A
authors.lastname: Gasnier
authors.affiliation: RTTQA, Royal Marsden Hospital, Fulham Road, London, UK.
authors.forename: Julia
authors.initials: J
authors.lastname: Henderson
authors.affiliation: Radiotherapy Trials QA Group (RTTQA), Mount Vernon Hospital, Northwood, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lee
authors.affiliation: Radiotherapy Trials QA Group (RTTQA), Mount Vernon Hospital, Northwood, UK.
authors.forename: Rushil
authors.initials: R
authors.lastname: Patel
authors.affiliation: Radiotherapy Trials QA Group (RTTQA), Mount Vernon Hospital, Northwood, UK.
authors.forename: Yatman
authors.initials: Y
authors.lastname: Tsang
authors.affiliation: Radiotherapy Trials QA Group (RTTQA), Mount Vernon Hospital, Northwood, UK.
authors.forename: Huiqi
authors.initials: H
authors.lastname: Yang
authors.affiliation: Radiotherapy Trials QA Group (RTTQA), Mount Vernon Hospital, Northwood, UK.
authors.forename: Rada
authors.initials: R
authors.lastname: Zotova
authors.affiliation: RTTQA, Royal Marsden Hospital, Fulham Road, London, UK.
authors.forename: Emma
authors.initials: E
authors.lastname: Wells
mesh_terms: D002986:Clinical Trials as Topic / Q000592:standards*; D003406:Credentialing; D011785:Quality Assurance, Health Care; D011874:Radiometry / Q000592:standards*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000592:standards; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D006113:United Kingdom
keywords: Dosimetry audit; IMRT; Quality assurance; Radiotherapy trials