title: Deviations in delineated GTV caused by artefacts in 4DCT.
abstract: OBJECTIVE
  Four-dimensional computed tomography (4DCT) is used for breathing-adapted radiotherapy planning. Irregular breathing, large tumour motion or interpolation of images can cause artefacts in the 4DCT. This study evaluates the impact of artefacts on gross tumour volume (GTV) size.
  
  
  METHODS
  In 19 4DCT scans of patients with peripheral lung tumours, GTV was delineated in all bins. Variations in GTV size between bins in each 4DCT scan were analysed and correlated to tumour motion and variations in breathing signal amplitude and breathing signal period. End-expiration GTV size (GTVexp) was considered as reference for GTV size. Intra-session delineation error was estimated by re-delineation of GTV in eight of the 4DCT scans.
  
  
  RESULTS
  In 16 of the 4DCT scans the maximum deviations from GTVexp were larger than could be explained by delineation error. The deviations were largest in the bins adjacent to the end-inspiration bin. The coefficient of variation of GTV size was significantly correlated to tumour motion in the cranio-caudal direction, but no significant correlation was found to breathing signal variations.
  
  
  CONCLUSIONS
  We found considerable variations in GTV size throughout the 4DCT scans. Awareness of the error introduced by artefacts is important especially if radiotherapy planning is based on a single 4DCT bin.
authors.affiliation: Department of Radiation Oncology, Rigshospitalet, Copenhagen, Denmark. gitte.persson@rh.regionh.dk
authors.forename: Gitte Fredberg
authors.initials: GF
authors.lastname: Persson
authors.forename: Ditte Eklund
authors.initials: DE
authors.lastname: Nygaard
authors.forename: Carsten
authors.initials: C
authors.lastname: Brink
authors.forename: Jonas Westberg
authors.initials: JW
authors.lastname: Jahn
authors.forename: Per
authors.initials: P
authors.lastname: Munck af Rosenschöld
authors.forename: Lena
authors.initials: L
authors.lastname: Specht
authors.forename: Stine Sofia
authors.initials: SS
authors.lastname: Korreman
mesh_terms: D016477:Artifacts; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy; D019583:Dose Fractionation, Radiation; D005260:Female; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy; D009038:Motion; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration; D012307:Risk Factors; D012494:Sampling Studies; D047368:Tumor Burden