title: Inter-scan and inter-observer tumour volume delineation variability on cone beam computed tomography in patients treated with stereotactic body radiation therapy for early-stage non-small cell lung cancer.
abstract: BACKGROUND
  Quantification of volume changes on cone beam computed tomography (CBCT) during lung stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC) may provide a useful radiological marker for radiation response and for adaptive treatment planning. This study quantifies inter-scan and inter-observer variability in tumour volume delineation on CBCT.
  
  
  METHODS
  Three clinicians independently contoured the primary gross tumour volume (GTV) manually on CBCTs taken immediately before SBRT treatment (pre) and after the same SBRT treatment (post) for 19 NSCLC patients. Relative volume differences (RVD) were calculated between the pre- and post-CBCTs for a given treatment and between any two of three observers for a given CBCT. Coefficient of variation (CV) was used to quantitatively measure and compare the extent of variability.
  
  
  RESULTS
  Inter-observer variability had a significantly higher CV of 0.15 ± 0.13 compared to inter-scan CV of 0.03 ± 0.04 with P < 0.0001. The greatest variability was observed with tumours (<2 cm in diameter) versus larger tumours with 95% limit of agreement (LOA) (Mean ± Standard Deviation) of 1.90% ± 19.55% vs. -0.97% ± 12.26% for inter-scan RVD and 29.99% ± 73.84% vs. 9.37% ± 29.95% for inter-observer RVD respectively.
  
  
  CONCLUSIONS
  Inter-observer variability was greater than inter-scan variability for tumour volume delineation on CBCT with greatest variability for small tumours (<2 cm in diameter). LOA for inter-scan variability (~12%) helps defines a threshold for clinically meaningful tumour volume change during SBRT treatment for tumours with diameter greater than 2 cm, with larger thresholds needed for smaller tumours.
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Hou
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: Vishesh
authors.initials: V
authors.lastname: Agrawal
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: John
authors.initials: J
authors.lastname: Romano
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Baldini
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Aileen B
authors.initials: AB
authors.lastname: Chen
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Kozono
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Killoran
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Wagar
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Fred L
authors.initials: FL
authors.lastname: Hacker
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Hugo Jwl
authors.initials: HJ
authors.lastname: Aerts
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Lewis
authors.affiliation: Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Raymond H
authors.initials: RH
authors.lastname: Mak
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy*; D008297:Male; D015588:Observer Variation; D016634:Radiosurgery / Q000379:methods*; D015203:Reproducibility of Results; D047368:Tumor Burden
keywords: 
  CBCT
  ; 
  NSCLC
  ; 
  SBRT
  ; inter-observer variability; inter-scan variability