title: Evaluation of geometric changes of parotid glands during head and neck cancer radiotherapy using daily MVCT and automatic deformable registration.
abstract: OBJECTIVE
  To assess and evaluate geometrical changes in parotid glands using deformable image registration and megavoltage CT (MVCT) images.
  
  
  METHODS
  A deformable registration algorithm was applied to 330 daily MVCT images (10 patients) to create deformed parotid contours. The accuracy and robustness of the algorithm was evaluated through visual review, comparison with manual contours, and precision analysis. Temporal changes in the parotid gland geometry were observed.
  
  
  RESULTS
  The deformed parotid contours were qualitatively judged to be acceptable. Compared with manual contours, the uncertainties of automatically deformed contours were similar with regard to geometry and dosimetric endpoint. The day-to-day variations (1 standard deviation of errors) in the center-of-mass distance and volume were 1.61mm and 4.36%, respectively. The volumes tended to decrease with a median total loss of 21.3% (6.7-31.5%) and a median change rate of 0.7%/day (0.4-1.3%/day). Parotids migrated toward the patient center with a median total distance change of -5.26mm (0.00 to -16.35mm) and a median change rate of -0.22mm/day (0.02 to -0.56mm/day).
  
  
  CONCLUSIONS
  The deformable image registration and daily MVCT images provide an efficient and reliable assessment of parotid changes over the course of a radiation therapy.
authors: Department of Radiation Oncology, M.D. Anderson Cancer Center Orlando, Orlando, FL 32806, USA. Choonik.Lee@orhs.org
authors: Choonik
authors: C
authors: Lee
authors: Katja M
authors: KM
authors: Langen
authors: Weiguo
authors: W
authors: Lu
authors: Jason
authors: J
authors: Haimerl
authors: Eric
authors: E
authors: Schnarr
authors: Kenneth J
authors: KJ
authors: Ruchala
authors: Gustavo H
authors: GH
authors: Olivera
authors: Sanford L
authors: SL
authors: Meeks
authors: Patrick A
authors: PA
authors: Kupelian
authors: Thomas D
authors: TD
authors: Shellenberger
authors: Rafael R
authors: RR
authors: Mañon
mesh_terms: D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D010306:Parotid Gland / Q000000981:diagnostic imaging / Q000528:radiation effects*; D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D036542:Tomography, Spiral Computed