title: Retrospective review of locally set tolerances for VMAT prostate patient specific QA using the COMPASS(®) system.
abstract: OBJECTIVE
  This study retrospectively reviewed locally set pass rates/tolerances for COMPASS(®) pre-treatment quality assurance results for RapidArc prostate plans to determine if these are appropriate. This was performed via quantifying the agreement between treatment planning system calculations and measurements based on absolute dose comparisons (3% tolerance for all dose points) and global gamma index assessment (3%/3 mm criterion for 97% of points).
  
  
  METHODS
  Seventy-three prostate one-arc RapidArc plans, delivered by four dosimetrically matched linacs, were measured using the MatriXX Evolution two-dimensional array and analysed using COMPASS(®) (v.3, IBA Dosimetry). For the planning target volumes (PTV) considered, the D99%, D50%, D1% and DMean differences were analysed. The percentage volume with gamma greater than 1, average gamma and DMean difference were investigated for all structures. Nine plans were also assessed across the linac fleet to investigate potential linac dependence of results.
  
  
  CONCLUSIONS
  Regarding PTV DMean differences, all plans fell within the 3% tolerance and mostly within 2%, although there was a relatively small systematic difference. The absolute percentage differences of average and median doses suggested a weak linac dependence of the results which was found to be clinically insignificant. New stricter tolerances were established both for dose comparisons and gamma evaluation. Correlation between the gamma pass rates and the differences in the D99%, D50% and D1% was found to be moderate suggesting that gamma analysis in isolation has questionable clinical meaning and should only be used to indicate outliers for further analysis.
authors.affiliation: Department of Radiation Physics, Queen's Centre for Oncology and Haematology, Hull and East Yorkshire Hospitals NHS Trust, UK. Electronic address: athina.sdrolia@hey.nhs.uk.
authors.forename: A
authors.initials: A
authors.lastname: Sdrolia
authors.affiliation: Department of Radiation Physics, Queen's Centre for Oncology and Haematology, Hull and East Yorkshire Hospitals NHS Trust, UK.
authors.forename: K M
authors.initials: KM
authors.lastname: Brownsword
authors.affiliation: Department of Radiation Physics, Queen's Centre for Oncology and Haematology, Hull and East Yorkshire Hospitals NHS Trust, UK.
authors.forename: J E
authors.initials: JE
authors.lastname: Marsden
authors.affiliation: Department of Radiation Physics, Queen's Centre for Oncology and Haematology, Hull and East Yorkshire Hospitals NHS Trust, UK.
authors.forename: K T
authors.initials: KT
authors.lastname: Alty
authors.affiliation: Department of Radiation Physics, Queen's Centre for Oncology and Haematology, Hull and East Yorkshire Hospitals NHS Trust, UK.
authors.forename: C S
authors.initials: CS
authors.lastname: Moore
authors.affiliation: Department of Radiation Physics, Queen's Centre for Oncology and Haematology, Hull and East Yorkshire Hospitals NHS Trust, UK.
authors.forename: A W
authors.initials: AW
authors.lastname: Beavis
mesh_terms: D000465:Algorithms; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011785:Quality Assurance, Health Care; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D035501:Uncertainty
keywords: 3D quality assurance; COMPASS; Tolerance; VMAT prostate