title: Fiducial-free real-time image-guided robotic radiosurgery for tumors of the sacrum/pelvis.
abstract: OBJECTIVE
  Radiosurgery is a non-invasive treatment for many spinal tumors. Sacral radiosurgery, however, requires invasive fiducial marker insertion to target and track the tumor's position. We present preliminary clinical results and phantom accuracy measurements of sacral radiosurgery using fiducial-free alignment based on vertebral anatomy distant to tumor location.
  
  
  METHODS
  Fifty-one lesions in 38 patients were treated using fiducial-free spinal tracking of the L5 vertebra. An anthropomorphic phantom was used for accuracy measurements of this approach. Dose planning was based on 1.0mm computer tomography slices using inverse treatment planning.
  
  
  RESULTS
  Tracked targets were up to 17cm from the treated tumor. Phantom tests produced an overall mean targeting error of 1.43mm (+/-0.47mm). Patient median follow-up was 12.7months. Local tumor control was 95%. Treatment doses were 12-25Gy with a median prescription isodose of 65% (40-70%) and tumor volumes between 1.3 and 152.8cc. No short-term adverse events were noted during the follow-up period.
  
  
  CONCLUSIONS
  Fiducial-free tracking of the lower lumbar vertebrae is a feasible, accurate, and reliable tool for radiosurgery of sacral and pelvic tumors. It is a valuable novel alternative to surgical procedures and conventional fractionated radiation therapy for these challenging cases.
authors: European Cyberknife Center Munich, Munich, Germany. Alexander.Muacevic@cyber-knife.net
authors: Alexander
authors: A
authors: Muacevic
authors: Christian
authors: C
authors: Drexler
authors: Markus
authors: M
authors: Kufeld
authors: Pantaleo
authors: P
authors: Romanelli
authors: Hans Juergen
authors: HJ
authors: Duerr
authors: Berndt
authors: B
authors: Wowra
mesh_terms: D004307:Dose-Response Relationship, Radiation; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation / Q000379:methods; D038361:Neuronavigation / Q000295:instrumentation / Q000379:methods; D010386:Pelvic Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D010388:Pelvis / Q000000981:diagnostic imaging / Q000601:surgery; D019047:Phantoms, Imaging; D011832:Radiation Injuries / Q000517:prevention & control; D011859:Radiography; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D018570:Risk Assessment; D012371:Robotics / Q000379:methods*; D012447:Sacrum / Q000000981:diagnostic imaging / Q000601:surgery*; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D025321:Surgery, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D013997:Time Factors; D016896:Treatment Outcome