title: A quality assurance method that utilizes 3D dosimetry and facilitates clinical interpretation.
abstract: OBJECTIVE
  To demonstrate a new three-dimensional (3D) quality assurance (QA) method that provides comprehensive dosimetry verification and facilitates evaluation of the clinical significance of QA data acquired in a phantom. Also to apply the method to investigate the dosimetric efficacy of base-of-skull (BOS) intensity-modulated radiotherapy (IMRT) treatment.
  
  
  METHODS
  Two types of IMRT QA verification plans were created for 6 patients who received BOS IMRT. The first plan enabled conventional 2D planar IMRT QA using the Varian portal dosimetry system. The second plan enabled 3D verification using an anthropomorphic head phantom. In the latter, the 3D dose distribution was measured using the DLOS/Presage dosimetry system (DLOS = Duke Large-field-of-view Optical-CT System, Presage Heuris Pharma, Skillman, NJ), which yielded isotropic 2-mm data throughout the treated volume. In a novel step, measured 3D dose distributions were transformed back to the patient's CT to enable calculation of dose-volume histograms (DVH) and dose overlays. Measured and planned patient DVHs were compared to investigate clinical significance.
  
  
  RESULTS
  Close agreement between measured and calculated dose distributions was observed for all 6 cases. For gamma criteria of 3%, 2 mm, the mean passing rate for portal dosimetry was 96.8% (range, 92.0%-98.9%), compared to 94.9% (range, 90.1%-98.9%) for 3D. There was no clear correlation between 2D and 3D passing rates. Planned and measured dose distributions were evaluated on the patient's anatomy, using DVH and dose overlays. Minor deviations were detected, and the clinical significance of these are presented and discussed.
  
  
  CONCLUSIONS
  Two advantages accrue to the methods presented here. First, treatment accuracy is evaluated throughout the whole treated volume, yielding comprehensive verification. Second, the clinical significance of any deviations can be assessed through the generation of DVH curves and dose overlays on the patient's anatomy. The latter step represents an important development that advances the clinical relevance of complex treatment QA.
authors.affiliation: Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710, USA. mark.oldham@duke.edu
authors.forename: Mark
authors.initials: M
authors.lastname: Oldham
authors.forename: Andrew
authors.initials: A
authors.lastname: Thomas
authors.forename: Jennifer
authors.initials: J
authors.lastname: O'Daniel
authors.forename: Titania
authors.initials: T
authors.lastname: Juang
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Ibbott
authors.forename: John
authors.initials: J
authors.lastname: Adamovics
authors.forename: John P
authors.initials: JP
authors.lastname: Kirkpatrick
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008577:Meningeal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D008579:Meningioma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D009442:Neurilemmoma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D009464:Neuroma, Acoustic / Q000000981:diagnostic imaging / Q000532:radiotherapy; D058958:Organs at Risk / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care / Q000379:methods / Q000592:standards*; D011859:Radiography; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods / Q000592:standards*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods / Q000592:standards*; D019292:Skull Base Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*