title: GTV delineation in supraglottic laryngeal carcinoma: interobserver agreement of CT versus CT-MR delineation.
abstract: BACKGROUND
  GTV delineation is the first crucial step in radiotherapy and requires high accuracy, especially with the growing use of highly conformal and adaptive radiotherapy techniques. If GTV delineations of observers concord, they are considered to be of high accuracy. The aim of the study is to determine the interobserver agreement for GTV delineations of supraglottic laryngeal carcinoma on CT and on CT combined with MR-images and to determine the effect of adding MR images to CT-based delineation on the delineated volume and the interobserver agreement.
  
  
  METHODS
  Twenty patients with biopsy proven T1-T4 supraglottic laryngeal cancer, treated with curative intent were included. For all patients a contrast enhanced planning CT and a 1.5-T MRI with gadolinium were acquired in the same head-and-shoulder mask for fixation as used during treatment. For MRI, a two element surface coil was used as a receiver coil. Three dedicated observers independently delineated the GTV on CT. After an interval of 2 weeks, a set of co-registered CT and MR-images was provided to delineate the GTV on CT. Common volumes (C) and encompassing volumes (E) were calculated and C/E ratios were determined for each pair of observers. The conformity index general (CIgen) was used to quantify the interobserver agreement.
  
  
  RESULTS
  In general, a large variation in interobserver agreement was found for CT (range: 0.29-0.77) as well as for CT-MR delineations (range: 0.17-0.80). The mean CIgen for CT (0.61) was larger compared to CT-MR (0.57) (p = 0.032). Mean GTV volume delineated on CT-MR (6.6 cm(3)) was larger compared to CT (5.6 cm(3)) (p = 0.002).
  
  
  CONCLUSIONS
  Delineation on CT with co-registered MR-images resulted in a larger mean GTV volume and in a decrease in interobserver agreement compared to CT only delineation for supraglottic laryngeal carcinoma.
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Q01.118; Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands. e.a.jager-3@umcutrecht.nl.
authors.forename: Elise Anne
authors.initials: EA
authors.lastname: Jager
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Q01.118; Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands. n.kasperts@umcutrecht.nl.
authors.forename: Nicolien
authors.initials: N
authors.lastname: Kasperts
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Q01.118; Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands. j.caldasmagalhaes-2@umcutrecht.nl.
authors.forename: Joana
authors.initials: J
authors.lastname: Caldas-Magalhaes
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Q01.118; Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands. m.philippens@umcutrecht.nl.
authors.forename: Mariëlle E P
authors.initials: ME
authors.lastname: Philippens
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Q01.118; Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands. f.a.pameijer@umcutrecht.nl.
authors.forename: Frank A
authors.initials: FA
authors.lastname: Pameijer
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Q01.118; Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands. c.h.j.terhaard@umcutrecht.nl.
authors.forename: Chris H J
authors.initials: CH
authors.lastname: Terhaard
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Q01.118; Heidelberglaan 100, 3584 CX, Utrecht, the Netherlands. c.p.j.raaijmakers@umcutrecht.nl.
authors.forename: Cornelis P J
authors.initials: CP
authors.lastname: Raaijmakers
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000473:pathology* / Q000532:radiotherapy; D005931:Glottis / Q000473:pathology*; D006801:Humans; D007822:Laryngeal Neoplasms / Q000473:pathology* / Q000532:radiotherapy; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015588:Observer Variation; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated; D014057:Tomography, X-Ray Computed / Q000379:methods*