title: Investigation of a real-time EPID-based patient dose monitoring safety system using site-specific control limits.
abstract: OBJECTIVE
  The aim of this study is to investigate the performance and limitations of a real-time transit electronic portal imaging device (EPID) dosimetry system for error detection during dynamic intensity modulated radiation therapy (IMRT) treatment delivery. Sites studied are prostate, head and neck (HN), and rectal cancer treatments.
  
  
  METHODS
  The system compares measured cumulative transit EPID image frames with predicted cumulative image frames in real-time during treatment using a χ comparison with 4 %, 4 mm criteria. The treatment site-specific thresholds (prostate, HN and rectum IMRT) were determined using initial data collected from 137 patients (274 measured treatment fractions) and a statistical process control methodology. These thresholds were then applied to data from 15 selected patients including 5 prostate, 5 HN, and 5 rectum IMRT treatments for system evaluation and classification of error sources.
  
  
  RESULTS
  Clinical demonstration of real-time transit EPID dosimetry in IMRT was presented. For error simulation, the system could detect gross errors (i.e. wrong patient, wrong plan, wrong gantry angle) immediately after EPID stabilisation; 2 seconds after the start of treatment. The average rate of error detection was 7.0 % (prostate = 5.6 %, HN= 8.7 % and rectum = 6.7 %). The detected errors were classified as either clinical in origin (e.g. patient anatomical changes), or non-clinical in origin (e.g. detection system errors). Classified errors were 3.2 % clinical and 3.9 % non-clinical.
  
  
  CONCLUSIONS
  An EPID-based real-time error detection method for treatment verification during dynamic IMRT has been developed and tested for its performance and limitations. The system is able to detect gross errors in real-time, however improvement in system robustness is required to reduce the non-clinical sources of error detection.
authors: Faculty of Engineering and Built Environment, School of Electrical Engineering and Computer Science, University of Newcastle, Newcastle, NSW, Australia. Todsaporn.fuangrod@uon.edu.au.
authors: Todsaporn
authors: T
authors: Fuangrod
authors: Faculty of Science and IT, School of Mathematical and Physical Sciences, The University of Newcastle, Newcastle, NSW, Australia.|Calvary Mater Newcastle Hospital, Newcastle, NSW, Australia.
authors: Peter B
authors: PB
authors: Greer
authors: Radiation Physics Laboratory Sydney Medical School, The University of Sydney, Sydney, NSW, Australia.
authors: Henry C
authors: HC
authors: Woodruff
authors: Faculty of Science and IT, School of Mathematical and Physical Sciences, The University of Newcastle, Newcastle, NSW, Australia.|Calvary Mater Newcastle Hospital, Newcastle, NSW, Australia.
authors: John
authors: J
authors: Simpson
authors: Calvary Mater Newcastle Hospital, Newcastle, NSW, Australia.
authors: Shashank
authors: S
authors: Bhatia
authors: Faculty of Science and IT, School of Mathematical and Physical Sciences, The University of Newcastle, Newcastle, NSW, Australia.|Central Coast Cancer Centre, Gosford, NSW, Australia.
authors: Benjamin
authors: B
authors: Zwan
authors: Division of Medical Physics, CancerCare Manitoba, Winnipeg, MB, Canada.|Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB, Canada.|Department of Radiology, University of Manitoba, Winnipeg, MB, Canada.
authors: Timothy A
authors: TA
authors: vanBeek
authors: Division of Medical Physics, CancerCare Manitoba, Winnipeg, MB, Canada.|Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB, Canada.|Department of Radiology, University of Manitoba, Winnipeg, MB, Canada.
authors: Boyd M C
authors: BM
authors: McCurdy
authors: Faculty of Engineering and Built Environment, School of Electrical Engineering and Computer Science, University of Newcastle, Newcastle, NSW, Australia.
authors: Richard H
authors: RH
authors: Middleton
mesh_terms: D000465:Algorithms; D003199:Computer Systems; D006801:Humans; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated
keywords: EPID; Real-time patient dose monitoring safety system; Statistical process control