title: Interstitial brachytherapy in the head and neck region: when has imaging for treatment planning to be performed?
abstract: OBJECTIVE
  The relation of real and virtual anatomy in 3D treatment planning is influencing the quality of a brachytherapy treatment. Aim of this study was to evaluate how far prior to plastic tube implantation for fractionated interstitial brachytherapy performed imaging is appropriate for treatment planning purposes in regard to iatrogenic, morphologic changes of anatomy.
  
  
  METHODS
  Until April 1, 2001, 51 patients were included in this examination. Primary tumor sites were in the base of tongue (35), oro-/hypopharynx (9), floor of the mouth (4) as well as soft palate (3). Cross section imaging (MRI) in all the patients was performed before and three to six days after implantation of plastic tubes. To evaluate the morphologic alterations due to implant procedure and postimplant edema, distances were measured between two anatomically clearly defined landmarks of whom one had to be invariant to applicator implantation.
  
  
  RESULTS
  Between two anatomical landmarks initially mean standard distances were measured: Vertebra-pharyngeal mucosa 1.46 cm, mandibular-pharyngeal wall 3.14 cm, mandibular tip-base of tongue 5.12 cm, tongue width 4.77 cm. The comparison of pre- and postimplant MRI then revealed mean distance alterations: Vertebra-pharyngeal mucosa 3.1 mm, mandibular-pharyngeal wall 4.2 mm, mandibular tip-base of tongue 5.9 mm, tongue width 6.0 mm.
  
  
  CONCLUSIONS
  Mean applicator induced anatomic deviations between 3.1 and 6.0 mm compared to pre-implant anatomy, can severely change the target dose distribution. Basis of 3D-treatment planning therefore has to be always postimplant cross sectional imaging with adequate soft tissue depiction.
authors.affiliation: Interdisciplinary Center of Brachytherapy, University Hospital of the Christian-Albrechts-University, Kiel, Germany. schultze@onco.uni-kiel.de
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schultze
authors.forename: Ralf
authors.initials: R
authors.lastname: Schneider
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kimmig
authors.forename: György
authors.initials: G
authors.lastname: Kovacs
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D003131:Combined Modality Therapy; D019583:Dose Fractionation, Radiation; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010039:Otorhinolaryngologic Neoplasms / Q000175:diagnosis / Q000532:radiotherapy* / Q000601:surgery; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant; D012680:Sensitivity and Specificity