title: A magnetic resonance imaging study of prostate deformation relative to implanted gold fiducial markers.
abstract: OBJECTIVE
  To describe prostate deformation during radiotherapy and determine the margins required to account for prostate deformation after setup to intraprostatic fiducial markers (FM).
  
  
  METHODS
  Twenty-five patients with T1c-T2c prostate cancer had three gold FMs implanted. The patients presented with a full bladder and empty rectum for two axial magnetic resonance imaging (MRI) scans using a gradient recalled echo (GRE) sequence capable of imaging the FMs. The MRIs were done at the time of radiotherapy (RT) planning and a randomly assigned fraction. A single observer contoured the prostate surfaces. They were entered into a finite element model and aligned using the centroid of the three FMs.
  
  
  RESULTS
  During RT, the prostate volume decreased by 0.5%/fraction (p = 0.03) and the FMs in-migrated by 0.05 mm/fraction (p < 0.05). Prostate deformation was unrelated to differential bladder and bowel filling, but was related to a transurethral resection of the prostate (TURP) (p = 0.003). The standard deviation for systematic uncertainty of prostate surface contouring was 0.8 mm and for FM centroid localization was 0.4 mm. The standard deviation of random interfraction prostate deformation was 1.5 mm and for FM centroid variability was 1.1 mm. These uncertainties from prostate deformation can be incorporated into a margin recipe to determine the total margins required for RT.
  
  
  CONCLUSIONS
  During RT, the prostate exhibited: volume decrease, deformation, and in-migration of FMs. Patients with TURPs were prone to prostate deformation.
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital and University of Toronto, Toronto, Canada.
authors.forename: Alan M
authors.initials: AM
authors.lastname: Nichol
authors.forename: Kristy K
authors.initials: KK
authors.lastname: Brock
authors.forename: Gina A
authors.initials: GA
authors.lastname: Lockwood
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Moseley
authors.forename: Tara
authors.initials: T
authors.lastname: Rosewall
authors.forename: Padraig R
authors.initials: PR
authors.lastname: Warde
authors.forename: Charles N
authors.initials: CN
authors.lastname: Catton
authors.forename: David A
authors.initials: DA
authors.lastname: Jaffray
mesh_terms: D000368:Aged; D020342:Finite Element Analysis; D006046:Gold; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009068:Movement; D011467:Prostate / Q000473:pathology* / Q000601:surgery; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000532:radiotherapy / Q000601:surgery; D019736:Prostheses and Implants; D015203:Reproducibility of Results; D020728:Transurethral Resection of Prostate
chemical_list: D006046:Gold