title: 3D dose verification using tomotherapy CT detector array.
abstract: OBJECTIVE
  To evaluate a three-dimensional dose verification method based on the exit dose using the onboard detector of tomotherapy.
  
  
  METHODS
  The study included 347 treatment fractions from 24 patients, including 10 prostate, 5 head and neck (HN), and 9 spinal stereotactic body radiation therapy (SBRT) cases. Detector sonograms were retrieved and back-projected to calculate entrance fluence, which was then forward-projected on the CT images to calculate the verification dose, which was compared with ion chamber and film measurement in the QA plans and with the planning dose in patient plans.
  
  
  RESULTS
  Root mean square (RMS) errors of 2.0%, 2.2%, and 2.0% were observed comparing the dose verification (DV) and the ion chamber measured point dose in the phantom plans for HN, prostate, and spinal SBRT patients, respectively. When cumulative dose in the entire treatment is considered, for HN patients, the error of the mean dose to the planning target volume (PTV) varied from 1.47% to 5.62% with a RMS error of 3.55%. For prostate patients, the error of the mean dose to the prostate target volume varied from -5.11% to 3.29%, with a RMS error of 2.49%. The RMS error of maximum doses to the bladder and the rectum were 2.34% (-4.17% to 2.61%) and 2.64% (-4.54% to 3.94%), respectively. For the nine spinal SBRT patients, the RMS error of the minimum dose to the PTV was 2.43% (-5.39% to 2.48%). The RMS error of maximum dose to the spinal cord was 1.05% (-2.86% to 0.89%).
  
  
  CONCLUSIONS
  An excellent agreement was observed between the measurement and the verification dose. In the patient treatments, the agreement in doses to the majority of PTVs and organs at risk is within 5% for the cumulative treatment course doses. The dosimetric error strongly depends on the error in multileaf collimator leaf opening time with a sensitivity correlating to the gantry rotation period.
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, VA 22908, USA. ks2mc@virginia.edu
authors.forename: Ke
authors.initials: K
authors.lastname: Sheng
authors.forename: Ryan
authors.initials: R
authors.lastname: Jones
authors.forename: Wensha
authors.initials: W
authors.lastname: Yang
authors.forename: Siddharth
authors.initials: S
authors.lastname: Saraiya
authors.forename: Bernard
authors.initials: B
authors.lastname: Schneider
authors.forename: Quan
authors.initials: Q
authors.lastname: Chen
authors.forename: Geoff
authors.initials: G
authors.lastname: Sobering
authors.forename: Gustavo
authors.initials: G
authors.lastname: Olivera
authors.forename: Paul
authors.initials: P
authors.lastname: Read
mesh_terms: D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D006801:Humans; D008297:Male; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D011786:Quality Control; D011832:Radiation Injuries; D011859:Radiography; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D016634:Radiosurgery / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061106:Radiotherapy Setup Errors; D012189:Retrospective Studies; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D047368:Tumor Burden