title: Variability in spine radiosurgery treatment planning - results of an international multi-institutional study.
abstract: BACKGROUND
  The aim of this study was to quantify the variability in spinal radiosurgery (SRS) planning practices between five international institutions, all member of the Elekta Spine Radiosurgery Research Consortium.
  
  
  METHODS
  Four institutions provided one representative patient case each consisting of the medical history, CT and MR imaging. A step-wise planning approach was used where, after each planning step a consensus was generated that formed the basis for the next planning step. This allowed independent analysis of all planning steps of CT-MR image registration, GTV definition, CTV definition, PTV definition and SRS treatment planning. In addition, each institution generated one additional SRS plan for each case based on intra-institutional image registration and contouring, independent of consensus results.
  
  
  RESULTS
  Averaged over the four cases, image registration variability ranged between translational 1.1 mm and 2.4 mm and rotational 1.1° and 2.0° in all three directions. GTV delineation variability was 1.5 mm in axial and 1.6 mm in longitudinal direction averaged for the four cases. CTV delineation variability was 0.8 mm in axial and 1.2 mm in longitudinal direction. CTV-to-PTV margins ranged between 0 mm and 2 mm according to institutional protocol. Delineation variability was 1 mm in axial directions for the spinal cord. Average PTV coverage for a single fraction18 Gy prescription was 87 ± 5 %; Dmin to the PTV was 7.5 ± 1.8 Gy averaged over all cases and institutions. Average Dmax to the PRV_SC (spinal cord + 1 mm) was 10.5 ± 1.6 Gy and the average Paddick conformity index was 0.69 ± 0.06.
  
  
  CONCLUSIONS
  Results of this study reflect the variability in current practice of spine radiosurgery in large and highly experienced academic centers. Despite close methodical agreement in the daily workflow, clinically significant variability in all steps of the treatment planning process was demonstrated. This may translate into differences in patient clinical outcome and highlights the need for consensus and established delineation and planning criteria.
authors.affiliation: Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany. toussaint_a@ukw.de.
authors.forename: André
authors.initials: A
authors.lastname: Toussaint
authors.affiliation: Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Richter
authors.affiliation: Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Frederick
authors.initials: F
authors.lastname: Mantel
authors.affiliation: Departments of Neurological Surgery and Radiation Oncology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Flickinger
authors.affiliation: William Beaumont Hospital, Royal Oak, MI, USA.
authors.forename: Inga Siiner
authors.initials: IS
authors.lastname: Grills
authors.affiliation: William Beaumont Hospital, Royal Oak, MI, USA.
authors.forename: Neelam
authors.initials: N
authors.lastname: Tyagi
authors.affiliation: Department of Radiation Oncology, Sunnybrook Odette Cancer Center, University of Toronto, Toronto, ON, Canada.
authors.forename: Arjun
authors.initials: A
authors.lastname: Sahgal
authors.affiliation: Princess Margaret Cancer Center, Toronto, ON, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Letourneau
authors.affiliation: University of Virginia School of Medicine, Charlottesville, VA, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Sheehan
authors.affiliation: University of Virginia School of Medicine, Charlottesville, VA, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Schlesinger
authors.affiliation: Departments of Neurological Surgery and Radiation Oncology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: Peter Carlos
authors.initials: PC
authors.lastname: Gerszten
authors.affiliation: Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany.|Division of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Guckenberger
mesh_terms: D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007391:International Cooperation; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D058958:Organs at Risk; D011874:Radiometry / Q000379:methods; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D013116:Spinal Cord / Q000528:radiation effects; D013125:Spinal Neoplasms / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
keywords: Delineation; Planning variability; Spine radiosurgery; Vertebral metastases