title: Patterns of epidural progression following postoperative spine stereotactic body radiotherapy: implications for clinical target volume delineation.
abstract: OBJECTIVE
  The authors performed a pattern-of-failure analysis, with a focus on epidural disease progression, in patients treated with postoperative spine stereotactic body radiotherapy (SBRT).
  
  
  METHODS
  Of the 70 patients with 75 spinal metastases (cases) treated with postoperative spine SBRT, there were 26 cases of local disease recurrence and 25 cases with a component of epidural disease progression. Twenty-four of the 25 cases had preoperative epidural disease with subsequent epidural disease progression, and this cohort was the focus of this epidural-specific pattern-of-failure investigation. Preoperative, postoperative, and follow-up MRI scans were reviewed, and epidural disease was characterized based on location according to a system in which the vertebral anatomy is divided into 6 sectors, with the anterior compartment comprising Sectors 1, 2, and 6, and the posterior compartment comprising Sectors 3, 4, and 5.
  
  
  RESULTS
  Patterns of epidural progression are reported specifically for the 24 cases with preoperative epidural disease and subsequent epidural progression. Epidural disease progression within the posterior compartment was observed to be significantly lower in those with preoperative epidural disease confined to the anterior compartment than in those with preoperative epidural disease involving both anterior and posterior compartments (56% vs. 93%, respectively; p = 0.047). In a high proportion of patients with epidural disease progression, treatment failure was found in the anterior compartment, including both those with preoperative epidural disease confined to the anterior compartment and those with preoperative epidural disease involving both anterior and posterior compartments (100% vs. 73%, respectively). When epidural disease was confined to the anterior compartment on the preoperative and postoperative MRIs, no epidural disease progression was observed in Sector 4, which is the most posterior sector. Postoperative epidural disease characteristics alone were not predictive of the pattern of epidural treatment failure.
  
  
  CONCLUSIONS
  Reviewing the extent of epidural disease on preoperative MRI is imperative when planning postoperative SBRT. When epidural disease is confined to the anterior epidural sectors pre- and postoperatively, covering the entire epidural space circumferentially with a prophylactic "donut" distribution may not be needed.
authors.affiliation: Departments of 1 Medical Imaging and.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Chan
authors.affiliation: Department of Radiation Oncology, Odette Cancer Centre, and.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Thibault
authors.affiliation: Departments of 3 Biostatistics and.
authors.forename: Eshetu G
authors.initials: EG
authors.lastname: Atenafu
authors.affiliation: Radiology, University Health Network, University of Toronto;
authors.forename: Eugene
authors.initials: E
authors.lastname: Yu
authors.affiliation: Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto; and.
authors.forename: B C
authors.initials: BC
authors.lastname: John Cho
authors.affiliation: Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto; and.
authors.forename: Daniel
authors.initials: D
authors.lastname: Letourneau
authors.affiliation: Department of Radiation Oncology, Odette Cancer Centre, and.
authors.forename: Young
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, Sunnybrook Health Sciences Centre, University of Toronto; 
authors.forename: Albert
authors.initials: A
authors.lastname: Yee
authors.affiliation: Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University of Toronto, Ontario, Canada.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Fehlings
authors.affiliation: Department of Radiation Oncology, Odette Cancer Centre, and.|Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto; and.
authors.forename: Arjun
authors.initials: A
authors.lastname: Sahgal
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002292:Carcinoma, Renal Cell / Q000473:pathology / Q000601:surgery*; D018450:Disease Progression; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000175:diagnosis / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000601:surgery*; D016634:Radiosurgery / Q000379:methods; D013125:Spinal Neoplasms / Q000601:surgery*; D013131:Spine / Q000601:surgery*; D055815:Young Adult
keywords: CTV = clinical target volume; ISRC = International Spine Radiosurgery Consortium; LC = local control; OS = overall survival; PTV = planning tumor volume; SBRT = stereotactic body radiotherapy; Vrec = recurrent tumor volume; epidural disease; local recurrence; malignant epidural spinal cord compression; oncology; patterns of failure; postoperative radiosurgery; spinal metastases; spine radiosurgery; stereotactic body radiotherapy