title: Quantifying interobserver variation in target definition in palliative radiotherapy.
abstract: OBJECTIVE
  To describe the degree of interobserver and intraobserver variability in target and field definition when using three-dimensional (3D) volume- vs. two-dimensional (2D) field-based planning.
  
  
  METHODS
  Standardized case scenario and diagnostic imaging for 9 palliative cases (3 bone metastases, 3 palliative lung cancer, and 3 abdominal pelvis soft-tissue disease) were presented to 5 study radiation oncologists. After a decision on what the intended anatomic target should be, observers created two sets of treatment fields, first using a 2D field-based and then a 3D volume-based planning approach. Percent overlap, under-coverage, and over-coverage were used to describe interobserver and intraobserver variations in target definition.
  
  
  RESULTS
  The degree of interobserver variation for 2D and 3D planning was similar with a degree of overlap of 76% (range, 56%-85%) and 74% (range, 55%-88%), respectively. When comparing the treatment fields defined by the same observer using the two different planning methods, the mean degree of overlap was 78%; over-coverage, 22%; and under-coverage, 41%. There was statistically significantly more under-coverage when field-based planning was used for bone metastases (33%) vs. other anatomic sites (16%) (p = 0.02). In other words, 2D planning is more likely to result in geographic misses in bone metastases compared with other areas.
  
  
  CONCLUSIONS
  In palliative radiotherapy clinically significant interobserver and intraobserver variation existed when using both field- and volume-based planning approaches. Strategies that would reduce this variability deserve further investigation.
authors.affiliation: Centro Oncologia Mendel & Associados, Toronto, Ontario, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Grabarz
authors.forename: Tony
authors.initials: T
authors.lastname: Panzarella
authors.forename: Andrea
authors.initials: A
authors.lastname: Bezjak
authors.forename: Michael
authors.initials: M
authors.lastname: Mclean
authors.forename: Christine
authors.initials: C
authors.lastname: Elder
authors.forename: Rebecca K S
authors.initials: RK
authors.lastname: Wong
mesh_terms: D000008:Abdominal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D001859:Bone Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000556:secondary; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D015588:Observer Variation; D010166:Palliative Care / Q000592:standards; D010386:Pelvic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D018787:Radiation Oncology / Q000592:standards; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012983:Soft Tissue Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*