title: Influence of the type of imaging on the delineation process during the treatment planning.
abstract: OBJECTIVE
  The aim of this study was to compare the intra- and interobserver contouring variability for structures with density of organ at risk in two types of tomography: kilovoltage computed tomography (KVCT) versus megavoltage computed tomography (MVCT). The intra- and interobserver differences were examined on both types of tomography for structures which simulate human tissue or organs.
  
  
  METHODS
  Six structures with density of the liver, bone, trachea, lung, soft tissue and muscle were created and used. For the measurements, the special water phantom with all structures was designed. To evaluate interobserver variability, five observers delineated the structures in both types of computed tomography (CT).
  
  
  RESULTS
  Intraobserver variability was in the range of 1-14% and was the largest for the liver. The observers segmented larger volumes on MVCT compared with KVCT for the trachea (79.56 ccm vs.74.91 ccm), lung (87.61 vs. 82.50), soft tissue (154.24 vs. 145.47) and muscle (164.01 vs. 157.89). For the liver (98.13 vs. 99.38) and bone (51.86 vs. 67.97), the volume on MVCT was smaller than KVCT. The statistically significant differences between observers were observed for structures with density of the liver, bone and soft tissue on KVCT and for the liver, lung and soft tissue on MVCT. For the structures with density of the trachea and muscles, there were no significant differences for both types of tomography.
  
  
  CONCLUSIONS
  During the contouring process the interobserver and intraobserver contouring uncertainty was larger on MVCT, especially for structures with HU near 80, compared with KVCT.
authors.affiliation: Radiotherapy Department I, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Weronika
authors.initials: W
authors.lastname: Jackowiak
authors.affiliation: Radiotherapy Department II, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Bąk
authors.affiliation: Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Kowalik
authors.affiliation: Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Ryczkowski
authors.affiliation: Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Skórska
authors.affiliation: Radiotherapy Department II, Greater Poland Cancer Centre, Poznan, Poland.
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Paszek-Widzińska
keywords: Delineation; Interobserver variability; Kilovoltage computed tomography; Megavoltage computed tomography