title: Image quality and dose distributions of three linac-based imaging modalities.
abstract: OBJECTIVE
  Linac-based patient imaging is possible with a variety of techniques using different photon energies. The purpose of this work is to compare three imaging systems operating at 6 MV, flattening free filter (FFF) 1 MV, and 121 kV.
  
  
  METHODS
  The dose distributions of all pretreatment set-up images (over 1,000) were retrospectively calculated on the planning computed tomography (CT) images for all patients with prostate and head-and-neck cancer treated at our institution in 2013. We analyzed the dose distribution and the dose to organs at risk.
  
  
  RESULTS
  For head-and-neck cancer patients, the imaging dose from 6-MV cone beam CT (CBCT) reached maximum values at around 8 cGy. The 1-MV CBCT dose was about 63-79 % of the 6-MV CBCT dose for all organs at risk. Planar imaging reduced the imaging dose from CBCT to 30-40 % for both megavoltage modalities. The dose from the kilovoltage CBCT was 4-10 % of the 6-MV CBCT dose. For prostate cancer patients, the maximum dose from 6-MV CBCT reached 13-15 cGy, and was reduced to 66-73 % for 1 MV. Planar imaging reduces the MV CBCT dose to 10-20 %. The kV CBCT dose is 15-20 % of the 6-MV CBCT dose, slightly higher than the dose from MV axes. The dose distributions differ markedly in response to the different beam profiles and dose-depth characteristics.
authors.affiliation: Klinik für Strahlentherapie und Radioonkologie, Universitätsklinikum des Saarlandes, Kirrberger Straße Geb. 6.5, 66421, Homburg/Saar, Deutschland, Yvonne.dzierma@uks.eu.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Dzierma
authors.forename: Evemarie
authors.initials: E
authors.lastname: Ames
authors.forename: Frank
authors.initials: F
authors.lastname: Nuesken
authors.forename: Jan
authors.initials: J
authors.lastname: Palm
authors.forename: Norbert
authors.initials: N
authors.lastname: Licht
authors.forename: Christian
authors.initials: C
authors.lastname: Rübe
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D010315:Particle Accelerators; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*