title: Radiochromic film-based quality assurance for CT-based high-dose-rate brachytherapy.
abstract: OBJECTIVE
  In the past, film dosimetry was developed into a powerful tool for external beam radiotherapy treatment verification and quality assurance. The objective of this work was the development and clinical testing of the EBT3 model GafChromic film based brachytherapy quality assurance (QA) system.
  
  
  METHODS
  Retrospective dosimetry study was performed to test a patient-specific QA system for preoperative endorectal brachytherapy that uses a radiochromic film dosimetry system. A dedicated phantom for brachytherapy applicator used for rectal cancer treatment was fabricated enabling us to compare calculated-to-measured dose distributions. Starting from the same criteria used for external beam intensity-modulated radiation therapy QA (3%, 3 mm), passing criteria for high- and low-dose gradient regions were subsequently determined. Finally, we investigated the QA system's sensitivity to controlled source positional errors on selected patient plans.
  
  
  RESULTS
  In low-dose gradient regions, measured dose distributions with criteria of 3%, 3 mm barely passed the test, as they showed 95% passing pixels. However, in the high-dose gradient region, a more stringent condition could be established. Both criteria of 2%, 3 mm and 3%, 2 mm with gamma function calculated using normalization to the same absolute dose value in both measured and calculated dose distributions, and matrix sizes rescaled to match each other showed more than 95% of pixels passing, on average, for 15 patient plans analyzed.
  
  
  CONCLUSIONS
  Although the necessity of the patient-specific brachytherapy QA needs yet to be justified, we described a radiochromic film dosimetry-based QA system that can be a part of the brachytherapy commissioning process, as well as yearly QA program.
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Radiation Oncology, Jewish General Hospital, McGill University, Montréal, Québec, Canada.
authors: Saeid
authors: S
authors: Asgharizadeh
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Radiation Oncology, Jewish General Hospital, McGill University, Montréal, Québec, Canada.
authors: Hamed
authors: H
authors: Bekerat
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Radiation Oncology, Jewish General Hospital, McGill University, Montréal, Québec, Canada.
authors: Alasdair
authors: A
authors: Syme
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Radiation Oncology, Jewish General Hospital, McGill University, Montréal, Québec, Canada.
authors: Saad
authors: S
authors: Aldelaijan
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Radiation Oncology, Jewish General Hospital, McGill University, Montréal, Québec, Canada.
authors: François
authors: F
authors: DeBlois
authors: Department of Radiation Oncology, Jewish General Hospital, McGill University, Montréal, Québec, Canada.
authors: Té
authors: T
authors: Vuong
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Medical Physics, McGill University Health Centre, Montréal, Québec, Canada.
authors: Michael
authors: M
authors: Evans
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada.
authors: Jan
authors: J
authors: Seuntjens
authors: Medical Physics Unit, McGill University, Montréal, Québec, Canada; Department of Radiation Oncology, Jewish General Hospital, McGill University, Montréal, Québec, Canada. Electronic address: slobodan.devic@mcgill.ca.
authors: Slobodan
authors: S
authors: Devic
mesh_terms: D001918:Brachytherapy / Q000379:methods / Q000592:standards*; D005373:Film Dosimetry; D006801:Humans; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care / Q000379:methods*; D011874:Radiometry; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated; D012004:Rectal Neoplasms / Q000532:radiotherapy*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
keywords: Brachytherapy; Quality assurance; Radiochromic film dosimetry