title: MRI guidance for accelerated partial breast irradiation in prone position: imaging protocol design and evaluation.
abstract: OBJECTIVE
  To design and evaluate a magnetic resonance imaging (MRI) protocol to be incorporated in the simulation process for external beam accelerated partial breast irradiation.
  
  
  METHODS
  An imaging protocol was developed based on an existing breast MRI technique with the patient in the prone position on a dedicated coil. Pulse sequences were customized to exploit T1 and T2 contrast mechanisms characteristic of lumpectomy cavities. A three-dimensional image warping algorithm was included to correct for geometric distortions related to nonlinearity of spatially encoding gradients. Respiratory motion, image distortions, and susceptibility artifacts of 3.5-mm titanium surgical clips were examined. Magnetic resonance images of volunteers were acquired repeatedly to analyze residual setup deviations resulting from breast tissue deformation.
  
  
  RESULTS
  The customized sequences generated high-resolution magnetic resonance images emphasizing lumpectomy cavity morphology. Respiratory motion was negligible with the subject in the prone position. The gradient-induced nonlinearity was reduced to less than 1 mm in a region 15 cm away from the isocenter of the magnet. Signal-void regions of surgical clips were 4 mm and 8 mm for spin echo and gradient echo images, respectively. Typical residual repositioning errors resulting from breast deformation were estimated to be 3 mm or less.
  
  
  CONCLUSIONS
  MRI guidance for accelerated partial breast irradiation with the patient in the prone position with adequate contrast, spatial fidelity, and resolution is possible.
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, CA, USA. ahn.2007@stanford.edu
authors.forename: Kang-Hyun
authors.initials: KH
authors.lastname: Ahn
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
authors.forename: Marcus T
authors.initials: MT
authors.lastname: Alley
authors.forename: Kathleen C
authors.initials: KC
authors.lastname: Horst
authors.forename: Gary
authors.initials: G
authors.lastname: Luxton
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Daniel
authors.forename: Dimitre
authors.initials: D
authors.lastname: Hristov
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001943:Breast Neoplasms / Q000473:pathology* / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods; D015412:Mastectomy, Segmental; D009068:Movement; D016684:Prone Position; D011878:Radiotherapy / Q000379:methods; D015203:Reproducibility of Results; D012119:Respiration; D049291:Seroma / Q000473:pathology*