title: Daily image guidance with cone-beam computed tomography for head-and-neck cancer intensity-modulated radiotherapy: a prospective study.
abstract: OBJECTIVE
  To report on a prospective clinical trial of the use of daily kilovoltage cone-beam computed tomography (CBCT) to evaluate the interfraction and residual error motion of patients undergoing intensity-modulated radiotherapy for head-and-neck cancer.
  
  
  METHODS
  Patients were treated with intensity-modulated radiotherapy with an Elekta linear accelerator using a mounted CBCT scanner. CBCT was performed before every treatment, and translational (but not rotational) corrections were performed. At least once per week, a CBCT scan was obtained after intensity-modulated radiotherapy. Variations were measured in the medial-lateral, superoinferior, and anteroposterior dimensions, as well as in the rotation around these axes.
  
  
  RESULTS
  A total of 28 consecutive patients (1,013 CBCT scans) were studied. The average interfraction shift was 1.4 +/- 1.4, 1.7 +/- 1.9, and 1.8 +/- 2.1 mm in the medial-lateral, superoinferior, and anteroposterior dimensions, respectively. The corresponding average residual error shifts were 0.7 +/- 0.8, 0.9 +/- 0.9, and 0.9 +/- 0.9 mm. These data indicate that in the absence of daily CBCT image-guided radiotherapy, a clinical target volume to planning target volume margin of 3.9, 4.1, and 4.9 mm is needed in the medial-lateral, superoinferior, and anteroposterior dimensions, respectively. With daily CBCT, corresponding margins of 1.6, 2.5, and 1.9 mm should be acceptable. Subgroup analyses showed that larynx cancers and/or intratreatment weight loss indicate a need for slightly larger clinical target volume to planning target volume margins.
  
  
  CONCLUSIONS
  The results of our study have shown that image-guided radiotherapy using CBCT for head-and-neck cancer is effective. These data suggest it allows a reduction in the clinical target volume to planning target volume margins by about 50%, which could facilitate future studies of dose escalation and/or improved toxicity reduction. Caution is particularly warranted for cases in which the targets are mobile (e.g., the tongue).
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University Hospital, Philadelphia, PA 19107-5097, USA.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Den
authors.forename: Anthony
authors.initials: A
authors.lastname: Doemer
authors.forename: Greg
authors.initials: G
authors.lastname: Kubicek
authors.forename: Greg
authors.initials: G
authors.lastname: Bednarz
authors.forename: James M
authors.initials: JM
authors.lastname: Galvin
authors.forename: William M
authors.initials: WM
authors.lastname: Keane
authors.forename: Ying
authors.initials: Y
authors.lastname: Xiao
authors.forename: Mitchell
authors.initials: M
authors.lastname: Machtay
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D002138:Calibration; D054893:Cone-Beam Computed Tomography; D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D011446:Prospective Studies; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*