title: Radial displacement of clinical target volume in node negative head and neck cancer.
abstract: OBJECTIVE
  To evaluate the radial displacement of clinical target volume in the patients with node negative head and neck (H&N) cancer and to quantify the relative positional changes compared to that of normal healthy volunteers.
  
  
  METHODS
  Three node-negative H&N cancer patients and five healthy volunteers were enrolled in this study. For setup accuracy, neck thermoplastic masks and laser alignment were used in each of the acquired computed tomography (CT) images. Both groups had total three sequential CT images in every two weeks. The lymph node (LN) level of the neck was delineated based on the Radiation Therapy Oncology Group (RTOG) consensus guideline by one physician. We use the second cervical vertebra body as a reference point to match each CT image set. Each of the sequential CT images and delineated neck LN levels were fused with the primary image, then maximal radial displacement was measured at 1.5 cm intervals from skull base (SB) to caudal margin of LN level V, and the volume differences at each node level were quantified.
  
  
  RESULTS
  The mean radial displacements were 2.26 (±1.03) mm in the control group and 3.05 (±1.97) in the H&N cancer patients. There was a statistically significant difference between the groups in terms of the mean radial displacement (p = 0.03). In addition, the mean radial displacement increased with the distance from SB. As for the mean volume differences, there was no statistical significance between the two groups.
  
  
  CONCLUSIONS
  This study suggests that a more generous radial margin should be applied to the lower part of the neck LN for better clinical target coverage and dose delivery.
authors.affiliation: Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Wan
authors.initials: W
authors.lastname: Jeon
authors.forename: Hong-Gyun
authors.initials: HG
authors.lastname: Wu
authors.forename: Sang Hyuk
authors.initials: SH
authors.lastname: Song
authors.forename: Jung-In
authors.initials: JI
authors.lastname: Kim
keywords: Head and neck neoplasms; Image-guided; Lymph nodes; Radiotherapy