title: Random positional variation among the skull, mandible, and cervical spine with treatment progression during head-and-neck radiotherapy.
abstract: OBJECTIVE
  With 54 degrees of freedom from the skull to mandible to C7, ensuring adequate immobilization for head-and-neck radiotherapy (RT) is complex. We quantify variations in skull, mandible, and cervical spine movement between RT sessions.
  
  
  METHODS
  Twenty-three sequential head-and-neck RT patients underwent serial computed tomography. Patients underwent planned rescanning at 11, 22, and 33 fractions for a total of 93 scans. Coordinates of multiple bony elements of the skull, mandible, and cervical spine were used to calculate rotational and translational changes of bony anatomy compared with the original planning scan.
  
  
  RESULTS
  Mean translational and rotational variations on rescanning were negligible, but showed a wide range. Changes in scoliosis and lordosis of the cervical spine between fractions showed similar variability. There was no correlation between positional variation and fraction number and no strong correlation with weight loss or skin separation. Semi-independent rotational and translation movement of the skull in relation to the lower cervical spine was shown. Positioning variability measured by means of vector displacement was largest in the mandible and lower cervical spine.
  
  
  CONCLUSIONS
  Although only small overall variations in position between head-and-neck RT sessions exist on average, there is significant random variation in patient positioning of the skull, mandible, and cervical spine elements. Such variation is accentuated in the mandible and lower cervical spine. These random semirigid variations in positioning of the skull and spine point to a need for improved immobilization and/or confirmation of patient positioning in RT of the head and neck.
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center and Albert Einstein College of Medicine, Bronx, NY, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Ahn
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Ahn
authors.forename: C Joe
authors.initials: CJ
authors.lastname: Lee
authors.forename: Jin
authors.initials: J
authors.lastname: Shen
authors.forename: Ekeni
authors.initials: E
authors.lastname: Miller
authors.forename: Alex
authors.initials: A
authors.lastname: Lukaj
authors.forename: Elissa
authors.initials: E
authors.lastname: Milan
authors.forename: Ravindra
authors.initials: R
authors.lastname: Yaparpalvi
authors.forename: Shalom
authors.initials: S
authors.lastname: Kalnicki
authors.forename: Madhur K
authors.initials: MK
authors.lastname: Garg
mesh_terms: D002574:Cervical Vertebrae / Q000000981:diagnostic imaging*; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D007103:Immobilization / Q000379:methods*; D008334:Mandible / Q000000981:diagnostic imaging*; D009068:Movement; D011446:Prospective Studies; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated; D012399:Rotation; D012886:Skull / Q000000981:diagnostic imaging*