title: A simplified CT-based definition of the lymph node levels in the node negative neck.
abstract: OBJECTIVE
  Using three dimensional (3D) conformal radiotherapy (CRT) techniques for elective neck irradiation (ENI) may allow for local disease control to be maintained while diminishing xerostomia by eliminating major salivary glands (or parts thereof) from the treatment portals. The standardization of CT based target volumes for the clinically negative (elective) neck is a prerequisite for 3DCRT. The aim of the present study was to substantially modify an existing ('original') CT-based protocol for the delineation of the neck target volume, into a more practical ('simplified') protocol. This will allow for rapid contouring and the implementation of conformal ENI in routine clinical procedures.
  
  
  METHODS
  An earlier ('original') version of the CT-based definition for elective neck node regions 2-5 was re-evaluated, using 15 planning CT scans of previously treated patients. The contouring guidelines were simplified by (1) using a smaller number of easily identifiable soft tissue- and bony anatomical landmarks, which in turn had to be identified in only a limited number of CT slices, and (2) by subsequently interpolating the contoured lymph node regions. The adequacy of target coverage and the sparing using both 'original' and 'simplified' delineation protocols was evaluated by DVH analysis after contouring the primary tumor, the neck and the major salivary glands in a patient with supraglottic laryngeal (SGL) carcinoma who was treated using a 3DCRT technique.
  
  
  RESULTS
  The BEV projections of the 'original' and the 'simplified' versions of the 3D elective neck target showed good agreement and were found to be reproducible. The DVH's of the target and parotid glands were not significantly different using both contouring protocols.
  
  
  CONCLUSIONS
  The 'simplified' protocol for the delineation of the 3D elective neck target produced both comparable target coverage and sparing of the major salivary glands. When used together with an interpolation program, this 'simplified' protocol substantial reduced the contouring time and makes ENI with sparing of the major salivary glands a practical and achievable goal.
authors.affiliation: Department of Radiation Oncology, University Hospital Rotterdam/Daniel den Hoed Cancer Center, The Netherlands.
authors.forename: O B
authors.initials: OB
authors.lastname: Wijers
authors.forename: P C
authors.initials: PC
authors.lastname: Levendag
authors.forename: T
authors.initials: T
authors.lastname: Tan
authors.forename: E B
authors.initials: EB
authors.lastname: van Dieren
authors.forename: J
authors.initials: J
authors.lastname: van Sörnsen de Koste
authors.forename: H
authors.initials: H
authors.lastname: van der Est
authors.forename: S
authors.initials: S
authors.lastname: Senan
authors.forename: P J
authors.initials: PJ
authors.lastname: Nowak
mesh_terms: D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D008198:Lymph Nodes / Q000000981:diagnostic imaging* / Q000528:radiation effects; D009333:Neck / Q000000981:diagnostic imaging*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D014057:Tomography, X-Ray Computed