title: Cone beam CT dose reduction in prostate radiotherapy using Likert scale methods.
abstract: OBJECTIVE
  To use a Likert scale method to optimize image quality (IQ) for cone beam CT (CBCT) soft-tissue matching for image-guided radiotherapy of the prostate.
  
  
  METHODS
  23 males with local/locally advanced prostate cancer had the CBCT IQ assessed using a 4-point Likert scale (4 = excellent, no artefacts; 3 = good, few artefacts; 2 = poor, just able to match; 1 = unsatisfactory, not able to match) at three levels of exposure. The lateral separations of the subjects were also measured. The Friedman test and Wilcoxon signed-rank tests were used to determine if the IQ was associated with the exposure level. We used the point-biserial correlation and a χ(2) test to investigate the relationship between the separation and IQ.
  
  
  RESULTS
  The Friedman test showed that the IQ was related to exposure (p = 2 × 10(-7)) and the Wilcoxon signed-rank test demonstrated that the IQ decreased as exposure decreased (all p-values <0.005). We did not find a correlation between the IQ and the separation (correlation coefficient 0.045), but for separations <35 cm, it was possible to use the lowest exposure parameters studied.
  
  
  CONCLUSIONS
  We can reduce exposure factors to 80% of those supplied with the system without hindering the matching process for all patients. For patients with lateral separations <35 cm, the exposure factors can be reduced further to 64% of the original values.
  
  
  CONCLUSIONS
  Likert scales are a useful tool for measuring IQ in the optimization of CBCT IQ for soft-tissue matching in radiotherapy image guidance applications.
authors.affiliation: 1 Departments of Medical Physics, City Hospital Campus, Nottingham University Hospitals NHS Trust, Nottingham.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Langmack
authors.affiliation: 1 Departments of Medical Physics, City Hospital Campus, Nottingham University Hospitals NHS Trust, Nottingham.
authors.forename: Louise A
authors.initials: LA
authors.lastname: Newton
authors.affiliation: 2 Departments of Radiotherapy, City Hospital Campus, Nottingham University Hospitals NHS Trust, Nottingham.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Jordan
authors.affiliation: 2 Departments of Radiotherapy, City Hospital Campus, Nottingham University Hospitals NHS Trust, Nottingham.
authors.forename: Ruth
authors.initials: R
authors.lastname: Smith
mesh_terms: D054893:Cone-Beam Computed Tomography; D006801:Humans; D008297:Male; D011467:Prostate / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*