title: Assessment of a 2D electronic portal imaging devices-based dosimetry algorithm for pretreatment andin-vivomidplane dose verification.
abstract: BACKGROUND
  The use of electronic portal imaging devices (EPIDs) is a method for the dosimetric verification of radiotherapy plans, both pretreatment andin vivo. The aim of this study is to test a 2D EPID-based dosimetry algorithm for dose verification of some plans inside a homogenous and anthropomorphic phantom andin vivoas well.
  
  
  METHODS
  Dose distributions were reconstructed from EPID images using a 2D EPID dosimetry algorithm inside a homogenous slab phantom for a simple 10 × 10 cm2box technique, 3D conformal (prostate, head-and-neck, and lung), and intensity-modulated radiation therapy (IMRT) prostate plans inside an anthropomorphic (Alderson) phantom and in the patients (one fractionin vivo) for 3D conformal plans (prostate, head-and-neck and lung).
  
  
  RESULTS
  The planned and EPID dose difference at the isocenter, on an average, was 1.7% for pretreatment verification and less than 3% for allin vivoplans, except for head-and-neck, which was 3.6%. The mean γ values for a seven-field prostate IMRT plan delivered to the Alderson phantom varied from 0.28 to 0.65. For 3D conformal plans applied for the Alderson phantom, all γ1% values were within the tolerance level for all plans and in both anteroposterior and posteroanterior (AP-PA) beams.
  
  
  CONCLUSIONS
  The 2D EPID-based dosimetry algorithm provides an accurate method to verify the dose of a simple 10 × 10 cm2field, in two dimensions, inside a homogenous slab phantom and an IMRT prostate plan, as well as in 3D conformal plans (prostate, head-and-neck, and lung plans) applied using an anthropomorphic phantom andin vivo. However, further investigation to improve the 2D EPID dosimetry algorithm for a head-and-neck case, is necessary.
authors.affiliation: Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran; Department of Medical Physics, School of Medicine, Rafsanjan University of Medical Sciences, Rafsanjan, Iran; Department of Medical Physics, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran.
authors.forename: Ali
authors.initials: A
authors.lastname: Jomehzadeh
authors.affiliation: Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Parvaneh
authors.initials: P
authors.lastname: Shokrani
authors.affiliation: Department of Radiation Oncology, Isfahan Milad Hospital, Isfahan, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Mohammadi
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Alireza
authors.initials: A
authors.lastname: Amouheidari
keywords: Algorithm; electronic portal imaging devices dosimetry; in vivo dosimetry; midplane; pretreatment verification