title: [Analysis of differences on delineation of the gross tumor volume (GTV) of nasopharyngeal carcinoma].
abstract: OBJECTIVE
  Accurate delineation of tumor target volume and organ at risk based on CT simulation, is essential in modern radiotherapy planning. It is also the basic requirement to improve the treatment outcome and quality of life in nasopharyngeal carcinoma (NPC). In this study, the impact factors on delineation of the gross tumor volume (GTV) of NPC were analysis. by comparing difference among various doctors' contours.
  
  
  METHODS
  Thirty cases of NPC treatment planning with contrast enhanced CT scan were reviewed. Primary GTV delineated by in-charged physician was defined as GTV1. Another GTV delineated by author and a radiologist was defined as GTV2, while GTV1 was concealed by the functions of the treatment planning system, the longest diameters of each axis of GTV were measured and recorded respectively as X(1), Y(1), Z(1), and X(2), Y(2), Z(2). The volumes of GTV were calculated as V1 and V2. Maximum permitted error (MPE) was 2 mm on X and Y axes and 3 mm on Z axis. Margin of each axis was compared to Coparable MPEs by matching t-test.
  
  
  RESULTS
  The differences on axes of X, Y, Z between GTV1 and GTV2 were 2.95+/-4.33, 6.24+/-7.52, 6.25+/-9.35, respectively (P</=0.001). GTV1 was universally delineated too much, 33.33%(10/30) of them were over contour of air cavity. In all of the cases, at least difference in 1 site was found, while 19 cases had differences in 3 or more sites. However, one third was deficient on Z axis.
  
  
  CONCLUSIONS
  The delineation of GTV of NPC varied by radiation oncologists remarkably. This should be taken into consideration as one of uncertainties in treatment planning designation. Further training of radiology for radiation oncologist to improve their imaging diagnosis ability and implementation of more advance imaging equipment are warranted.
authors.affiliation: Department of Nasopharyngeal Carcinoma, Cancer Hospital, Shantou University Medical College, Shantou, Guangdong, 515031, P.R.China. pxpx@21cn.com
authors.forename: Xun
authors.initials: X
authors.lastname: Peng
authors.forename: Zhi-Xiong
authors.initials: ZX
authors.lastname: Lin
authors.forename: Wei-Bin
authors.initials: WB
authors.lastname: Lin
authors.forename: De-Rui
authors.initials: DR
authors.lastname: Li
authors.forename: Hong-Guang
authors.initials: HG
authors.lastname: Hong
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000532:radiotherapy; D015588:Observer Variation; D020266:Radiotherapy, Conformal; D014057:Tomography, X-Ray Computed / Q000379:methods*