title: Evaluation of a 2D diode array for IMRT quality assurance.
abstract: OBJECTIVE
  The QA of intensity modulated radiotherapy (IMRT) dosimetry is a laborious task. The goal of this work is to evaluate the dosimetric characteristics of a new 2D diode array (MapCheck from Sun Nuclear Corporation, Melbourne, Florida) and assess the role it can play in routine IMRT QA.
  
  
  METHODS
  Fundamental properties of the MapCheck such as reproducibility, linearity and temperature dependence are studied for high-energy photon beams. The accuracy of the correction for difference of diode sensitivity is also assessed. The diode array is benchmarked against film and ion chambers for conventional and IMRT treatments. The MapCheck sensitivity to multileaf collimator position errors is determined.
  
  
  RESULTS
  The diode array response is linear with dose up to 295 cGy. All diodes are calibrated to within +/-1% of each other, and mostly within +/-0.5%. The MapCheck readings are reproducible to within a maximum SD of +/-0.15%. A temperature dependence of 0.57%/ degrees C was noted and should be taken into account for absolute dosimetric measurement. Clinical performance of the MapCheck for relative and absolute dosimetry is demonstrated with seven beam (6 MV) head and neck IMRT plans, and compares well with film and ion chamber measurements. Comparison to calculated dose maps demonstrates that the planning system model underestimates the dose gradients in the penumbra region.
  
  
  CONCLUSIONS
  The MapCheck offers the dosimetric characteristics required for performing both relative and absolute dose measurements. Its use in the clinic can simplify and reduce the IMRT QA workload.
authors.affiliation: Department of Radiation Oncology, William Beaumont Hospital, 3601 W. Thirteen Mile Road, Royal Oak, MI 48073, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Létourneau
authors.forename: Misbah
authors.initials: M
authors.lastname: Gulam
authors.forename: Di
authors.initials: D
authors.lastname: Yan
authors.forename: Mark
authors.initials: M
authors.lastname: Oldham
authors.forename: John W
authors.initials: JW
authors.lastname: Wong
mesh_terms: D004307:Dose-Response Relationship, Radiation; D005373:Film Dosimetry; D006801:Humans; D019047:Phantoms, Imaging; D011786:Quality Control; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D011882:Radiotherapy, High-Energy; D012307:Risk Factors; D012680:Sensitivity and Specificity