title: Applicator reconstruction in MRI 3D image-based dose planning of brachytherapy for cervical cancer.
abstract: OBJECTIVE
  To elaborate a method for applicator reconstruction for MRI-based brachytherapy for cervical cancer.
  
  
  METHODS
  Custom-made plastic catheters with a copper sulphate solution were made for insertion in the source channels of MR-CT compatible applicators: plastic and titanium tandem ring applicators, and titanium needles. The applicators were CT and MR scanned in a phantom for accurate 3D assessment of applicator visibility and geometry. A reconstruction method was developed and evaluated in 19 patient MR examinations with ring applicator (plastic: 14, titanium: 5). MR applicator reconstruction uncertainties related to inter-observer variation were evaluated.
  
  
  RESULTS
  The catheters were visible in the plastic applicator on T1-weighted images in phantom and in 14/14 clinical applications. On T2-weighted images, the catheters appeared weaker but still visible in phantom and in 13/14 MR clinical applications. In the titanium applicator, the catheters could not be separated from the artifacts from the applicator itself. However, these artifacts could be used to localize both titanium ring applicator (5/5 clinical applications) and needles (6/6 clinical applications). Standard deviations of inter-observer differences were below 2 mm in all directions.
  
  
  CONCLUSIONS
  3D applicator reconstruction based on MR imaging could be performed for plastic and titanium applicators. Plastic applicators proved well to be suited for MRI-based reconstruction. For improved practicability of titanium applicator reconstruction, development of MR applicator markers is essential. Reconstruction of titanium applicator and needles at 1.5 T MR requires geometric evaluations in phantoms before using the applicator in patients.
authors.affiliation: Department of Biomedical Engineering, Aarhus University Hospital, Aarhus, Denmark. sha@mta.aaa.dk
authors.forename: Søren
authors.initials: S
authors.lastname: Haack
authors.forename: Søren Kynde
authors.initials: SK
authors.lastname: Nielsen
authors.forename: Jacob Christian
authors.initials: JC
authors.lastname: Lindegaard
authors.forename: John
authors.initials: J
authors.lastname: Gelineck
authors.forename: Kari
authors.initials: K
authors.lastname: Tanderup
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015588:Observer Variation; D011880:Radiotherapy Planning, Computer-Assisted; D014025:Titanium; D014057:Tomography, X-Ray Computed; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*
chemical_list: D014025:Titanium