title: Target delineation variability and corresponding margins of peripheral early stage NSCLC treated with stereotactic body radiotherapy.
abstract: OBJECTIVE
  To quantify the target delineation variability in peripheral early stage lung cancer treated with SBRT and derive corresponding margins.
  
  
  METHODS
  Sixteen early stage NSCLC GTV's were delineated by 11 radiation oncologists from 4 institutes. A median surface was computed and the delineation variation perpendicular to this surface was measured (local standard deviation=SD). The overall target delineation variability was quantified by the root-mean-square (rms) of the local SD. The required margin was determined by expanding all delineations to encompass the median surface, where after the underlying probability distribution was modeled by a number of uncorrelated 'pimples-and-dimples'.
  
  
  RESULTS
  The overall target delineation variability was 2.1mm (rms). Institute I-III delineated significantly smaller volumes than institute IV, yielding target delineation variabilities of 1.2mm and 1.8mm respectively. The margin required to obtain 90% coverage of the delineated contours was 3.4mm and 5.9mm respectively. The factor α in M=αΣ required to calculate adequate margins was 2.8-3.2, which is larger than the 2.5 found for 3D rigid target displacement.
  
  
  CONCLUSIONS
  A relatively small target delineation uncertainty of 1.2mm-1.8mm (1SD) was observed for early stage NSCLC. A 3.4-5.9mm GTV-to-PTV margin was required to account for this uncertainty alone, ignoring other sources of geometric uncertainties.
authors.affiliation: The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Heike
authors.initials: H
authors.lastname: Peulen
authors.affiliation: The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: José
authors.initials: J
authors.lastname: Belderbos
authors.affiliation: Department of Radiation Oncology, University of Wuerzburg, Germany; Department of Radiation Oncology, University Hospital Zurich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Guckenberger
authors.affiliation: University of Toronto and Princess Margaret Cancer Center, Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Hope
authors.affiliation: Beaumont Hospital, Royal Oak, USA.
authors.forename: Inga
authors.initials: I
authors.lastname: Grills
authors.affiliation: The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
authors.affiliation: The Netherlands Cancer Institute, Amsterdam, The Netherlands. Electronic address: j.sonke@nki.nl.
authors.forename: Jan-Jakob
authors.initials: JJ
authors.lastname: Sonke
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D009367:Neoplasm Staging; D014057:Tomography, X-Ray Computed / Q000379:methods; D035501:Uncertainty
keywords: NSCLC; PTV margins; SBRT; Target delineation