title: Online planning and delivery technique for radiotherapy of spinal metastases using cone-beam CT: image quality and system performance.
abstract: OBJECTIVE
  To assess the feasibility of an online strategy for palliative radiotherapy (RT) of spinal bone metastasis, which integrates imaging, planning, and treatment delivery in a single step at the treatment unit. The technical challenges of this approach include cone-beam CT (CBCT) image quality for target definition, online planning, and efficient process integration.
  
  
  METHODS
  An integrated imaging, planning, and delivery system was constructed and tested with phantoms. The magnitude of CBCT image artifacts following the use of an antiscatter grid and a nonlinear scatter correction was quantified using phantom data and images of patients receiving conventional palliative RT of the spine. The efficacy of online planning was then assessed using corrected CBCT images. Testing of the complete process was performed on phantoms with assessment of timing and dosimetric accuracy.
  
  
  RESULTS
  The use of image corrections reduced the cupping artifact from 30% to 4.5% on CBCT images of a body phantom and improved the accuracy of CBCT numbers (water: +/- 20 Hounsfield unit [HU], and lung and bone: to within +/- 130 HU). Bony anatomy was clearly visible and was deemed sufficient for target definition. The mean total time (n = 5) for application of the online approach was 23.1 min. Image-guided dose placement was assessed using radiochromic film measurements with good agreement (within 5% of dose difference and 2 mm of distance to agreement).
  
  
  CONCLUSIONS
  The technical feasibility of CBCT-guided online planning and delivery for palliative single treatment has been demonstrated. The process was performed in one session equivalent to an initial treatment slot (<30 min) with dosimetric accuracy satisfying accepted RT standards.
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario, Canada. daniel.letourneau@rmp.uhn.on.ca
authors.forename: Daniel
authors.initials: D
authors.lastname: Létourneau
authors.forename: Rebecca
authors.initials: R
authors.lastname: Wong
authors.forename: Douglas
authors.initials: D
authors.lastname: Moseley
authors.forename: Michael B
authors.initials: MB
authors.lastname: Sharpe
authors.forename: Stephen
authors.initials: S
authors.lastname: Ansell
authors.forename: Mary
authors.initials: M
authors.lastname: Gospodarowicz
authors.forename: David A
authors.initials: DA
authors.lastname: Jaffray
mesh_terms: D016477:Artifacts; D002138:Calibration; D004867:Equipment Design; D005240:Feasibility Studies; D006801:Humans; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D013125:Spinal Neoplasms / Q000532:radiotherapy* / Q000556:secondary; D013679:Technology, Radiologic / Q000295:instrumentation