title: First Experience With Real-Time EPID-Based Delivery Verification During IMRT and VMAT Sessions.
abstract: OBJECTIVE
  Gantry-mounted megavoltage electronic portal imaging devices (EPIDs) have become ubiquitous on linear accelerators. WatchDog is a novel application of EPIDs, in which the image frames acquired during treatment are used to monitor treatment delivery in real time. We report on the preliminary use of WatchDog in a prospective study of cancer patients undergoing intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) and identify the challenges of clinical adoption.
  
  
  METHODS
  At the time of submission, 28 cancer patients (head and neck, pelvis, and prostate) undergoing fractionated external beam radiation therapy (24 IMRT, 4 VMAT) had ≥1 treatment fraction verified in real time (131 fractions or 881 fields). EPID images acquired continuously during treatment were synchronized and compared with model-generated transit EPID images within a frame time (∼0.1 s). A χ comparison was performed to cumulative frames to gauge the overall delivery quality, and the resulting pass rates were reported graphically during treatment delivery. Every frame acquired (500-1500 per fraction) was saved for postprocessing and analysis.
  
  
  RESULTS
  The system reported the mean ± standard deviation in real time χ 91.1% ± 11.5% (83.6% ± 13.2%) for cumulative frame χ analysis with 4%, 4 mm (3%, 3 mm) criteria, global over the integrated image.
  
  
  CONCLUSIONS
  A real-time EPID-based radiation delivery verification system for IMRT and VMAT has been demonstrated that aims to prevent major mistreatments in radiation therapy.
authors.affiliation: Faculty of Science and Information Technology, School of Mathematical and Physical Sciences, University of Newcastle, New South Wales, Australia. Electronic address: henry.woodruff@newcastle.edu.au.
authors.forename: Henry C
authors.initials: HC
authors.lastname: Woodruff
authors.affiliation: Faculty of Engineering and Built Environment, School of Electrical Engineering and Computer Science, University of Newcastle, New South Wales, Australia.
authors.forename: Todsaporn
authors.initials: T
authors.lastname: Fuangrod
authors.affiliation: Division of Medical Physics, CancerCare Manitoba, Winnipeg, Manitoba, Canada; Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada; Department of Radiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Eric
authors.initials: E
authors.lastname: Van Uytven
authors.affiliation: Division of Medical Physics, CancerCare Manitoba, Winnipeg, Manitoba, Canada; Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada; Department of Radiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Boyd M C
authors.initials: BM
authors.lastname: McCurdy
authors.affiliation: Division of Medical Physics, CancerCare Manitoba, Winnipeg, Manitoba, Canada; Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada; Department of Radiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Timothy
authors.initials: T
authors.lastname: van Beek
authors.affiliation: Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales, Australia.
authors.forename: Shashank
authors.initials: S
authors.lastname: Bhatia
authors.affiliation: Faculty of Science and Information Technology, School of Mathematical and Physical Sciences, University of Newcastle, New South Wales, Australia; Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales, Australia.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Greer
mesh_terms: D016009:Chi-Square Distribution; D005740:Gases; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D010315:Particle Accelerators / Q000295:instrumentation*; D010386:Pelvic Neoplasms / Q000532:radiotherapy*; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011859:Radiography; D011874:Radiometry / Q000295:instrumentation; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging
chemical_list: D005740:Gases