title: Assessment of cone beam CT registration for prostate radiation therapy: fiducial marker and soft tissue methods.
abstract: BACKGROUND
  This investigation aimed to assess the consistency and accuracy of radiation therapists (RTs) performing cone beam computed tomography (CBCT) alignment to fiducial markers (FMs) (CBCTFM ) and the soft tissue prostate (CBCTST ).
  
  
  METHODS
  Six patients receiving prostate radiation therapy underwent daily CBCTs. Manual alignment of CBCTFM and CBCTST was performed by three RTs. Inter-observer agreement was assessed using a modified Bland-Altman analysis for each alignment method. Clinically acceptable 95% limits of agreement with the mean (LoAmean ) were defined as ±2.0 mm for CBCTFM and ±3.0 mm for CBCTST . Differences between CBCTST alignment and the observer-averaged CBCTFM (AvCBCTFM ) alignment were analysed. Clinically acceptable 95% LoA were defined as ±3.0 mm for the comparison of CBCTST and AvCBCTFM .
  
  
  RESULTS
  CBCTFM and CBCTST alignments were performed for 185 images. The CBCTFM 95% LoAmean were within ±2.0 mm in all planes. CBCTST 95% LoAmean were within ±3.0 mm in all planes. Comparison of CBCTST with AvCBCTFM resulted in 95% LoA of -4.9 to 2.6, -1.6 to 2.5 and -4.7 to 1.9 mm in the superior-inferior, left-right and anterior-posterior planes, respectively.
  
  
  CONCLUSIONS
  Significant differences were found between soft tissue alignment and the predicted FM position. FMs are useful in reducing inter-observer variability compared with soft tissue alignment. Consideration needs to be given to margin design when using soft tissue matching due to increased inter-observer variability. This study highlights some of the complexities of soft tissue guidance for prostate radiation therapy.
authors: Radiation Therapy Services, Radiation Oncology Mater Centre, Brisbane, Queensland, Australia; Science and Engineering Faculty, Queensland University of Technology, Brisbane, Queensland, Australia.
authors: Timothy
authors: T
authors: Deegan
authors: Rebecca
authors: R
authors: Owen
authors: Tanya
authors: T
authors: Holt
authors: Andrew
authors: A
authors: Fielding
authors: Jennifer
authors: J
authors: Biggs
authors: Matthew
authors: M
authors: Parfitt
authors: Alicia
authors: A
authors: Coates
authors: Lisa
authors: L
authors: Roberts
mesh_terms: D000368:Aged; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation* / Q000379:methods; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D056888:Patient Positioning / Q000295:instrumentation* / Q000379:methods; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique / Q000295:instrumentation*; D016896:Treatment Outcome
keywords: cone beam computed tomography; image-guided; observer variation; prostate; radiotherapy