title: Correction of diffusion-weighted magnetic resonance imaging for brachytherapy of locally advanced cervical cancer.
abstract: BACKGROUND
  Geometrical distortion is a major obstacle for the use of echo planar diffusion-weighted magnetic resonance imaging (DW-MRI) in planning of radiotherapy. This study compares geometrical distortion correction methods of DW-MRI at time of brachytherapy (BT) in locally advanced cervical cancer patients.
  
  
  METHODS
  In total 21 examinations comprising DW-MRI, dual gradient echo (GRE) for B₀ field map calculation and T2-weighted (T2W) fat-saturated MRI of eight patients with locally advanced cervical cancer were acquired during BT with a plastic tandem and ring applicator in situ. The ability of B0 field map correction (B₀M) and deformable image registration (DIR) to correct DW-MRI geometric image distortion was compared to the non-corrected DW-MRI including evaluation of apparent diffusion coefficient (ADC) for the gross tumor volume (GTV).
  
  
  RESULTS
  Geometrical distortion correction decreased tandem displacement from 3.3 ± 0.9 mm (non-corrected) to 2.9 ± 1.0 mm (B₀M) and 1.9 ± 0.6 mm (DIR), increased mean normalized cross-correlation from 0.69 ± 0.1 (non- corrected) to 0.70 ± 0.10 (B₀M) and 0.77 ± 0.1 (DIR), and increased the Jaccard similarity coefficient from 0.72 ± 0.1 (non-corrected) to 0.73 ± 0.06 (B₀M) and 0.77 ± 0.1 (DIR). For all parameters only DIR corrections were significant (p < 0.05). ADC of the GTV did not change significantly with either correction method.
  
  
  CONCLUSIONS
  DIR significantly improved geometrical accuracy of DW-MRI, with remaining residual uncertainties of less than 2 mm, while no significant improvement was seen using B₀ field map correction.
authors.affiliation: Department of Clinical Engineering, Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Søren
authors.initials: S
authors.lastname: Haack
authors.forename: Jesper F
authors.initials: JF
authors.lastname: Kallehauge
authors.forename: Sune N
authors.initials: SN
authors.lastname: Jespersen
authors.forename: Jacob C
authors.initials: JC
authors.lastname: Lindegaard
authors.forename: Kari
authors.initials: K
authors.lastname: Tanderup
authors.forename: Erik M
authors.initials: EM
authors.lastname: Pedersen
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004574:Electromagnetic Fields; D005260:Female; D006801:Humans; D015203:Reproducibility of Results; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy*