title: CyberKnife stereotactic radiotherapy for spinal tumors: value of computed tomographic myelography in spinal cord delineation.
abstract: OBJECTIVE
  For para- and intraspinal tumors, precise spinal cord delineation is critical for CyberKnife (Accuray, Inc., Sunnyvale, CA) stereotactic radiotherapy. We evaluated whether computed tomographic (CT) myelography is superior to magnetic resonance imaging (MRI) for accurate spinal cord delineation. Treatment parameters and short-term outcome and toxicity are also presented.
  
  
  METHODS
  The planning CT scan, the gadolinium-enhanced, T1-weighted, 3-dimensional (3D) fast imaging employing steady-state acquisition MRI scan, and the CT myelogram were fused before volume-of-interest delineation. The planning target volume margin was less than 1 mm using the Xsight Spine tracking system (Accuray). We present data from 11 heavily pretreated patients who underwent CyberKnife stereotactic radiosurgery between November 2006 and January 2008.
  
  
  RESULTS
  Spatial resolution was 0.46 and 0.93 mm/pixel for CT myelography and 3D-fast imaging employing steady-state acquisition MRI, respectively. The contrast between cerebrospinal fluid and spinal cord was excellent with CT myelography. A transient postmyelography headache occurred in 1 patient. The mean gross tumor volume was 51.1 mL. The mean prescribed dose was 34 Gy in 4 fractions (range, 2-7 fractions) with 147 beams (range, 79-232 beams) to the 75% reference isodose line (range, 68-80%), covering 95% (range, 86-99%) of the gross tumor volume with a mean conformity index of 1.4 (range, 1.1-1.8). No short-term toxicity on the spinal cord was noted at 1- to 6-months of follow-up.
  
  
  CONCLUSIONS
  CT myelography was more accurate for spinal cord delineation than 3D-fast imaging employing steady-state acquisition MRI (used for its myelographic effect), particularly in the presence of ferromagnetic artifacts in heavily pretreated patients or in patients with severe spinal compression. Because other MRI sequences (T2 and gadolinium-enhanced T1) provide excellent tumor characterization, we suggest trimodality imaging for spinal tumor treatment to yield submillimetric delineation accuracy. Combined with CyberKnife technology, CT myelography can improve the feasibility of dose escalation or reirradiation of spinal tumors in selected patients, thereby increasing local control while avoiding myelopathy. Further follow-up and prospective studies are warranted.
authors.affiliation: Department of Radiation Oncology, Antoine Lacassagne Anti-Cancer Center, Sophia Antipolis University, Nice, France. jthariat@hotmail.com
authors.forename: Juliette
authors.initials: J
authors.lastname: Thariat
authors.forename: Joel
authors.initials: J
authors.lastname: Castelli
authors.forename: Stephane
authors.initials: S
authors.lastname: Chanalet
authors.forename: Serge
authors.initials: S
authors.lastname: Marcie
authors.forename: Hamid
authors.initials: H
authors.lastname: Mammar
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: Bondiau
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009192:Myelography / Q000295:instrumentation / Q000379:methods*; D011877:Radionuclide Imaging; D016634:Radiosurgery; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed