title: Local tumor control after retreatment of spinal metastasis using stereotactic body radiotherapy; comparison with initial treatment group.
abstract: BACKGROUND
  The aim of this study is to evaluate local control rates after stereotactic body radiotherapy (SBRT) in recurrent spinal metastasis after external beam radiotherapy (EBRT) and new spinal metastatic lesions.
  
  
  METHODS
  Retrospective review of medical records and radiological data was performed on 54 retreatment and 131 initial SBRT patients. To compare various fractionation schedules, the biologically effective dose (BED) was applied. SBRT dose was calculated with linear-quadratic model and normalized to a 2-Gy equivalent dose (nBED, α/β =2 Gy for spinal cord, α/β =10 Gy for tumor). Doses to a point within the spinal cord that received the maximum dose (Pmax) were checked. Local control failure was defined as progression by imaging study. Overall survival, progression free survival, delivered radiation dose to tumor and spinal cord, and spinal cord Pmax nBED were compared in two groups.
  
  
  RESULTS
  The mean delivered radiation doses to tumor margin during SBRT were 51.1 Gy2/10 (retreatment) and 50.7 Gy2/10 (initial treatment). Mean survival was 29.6 months (overall)/20.7 months (retreatment)/ 32.4 months (initial treatment). Mean progression free period was 23.9 months (overall)/18.0 months (retreatment)/ 26.0 months (initial treatment). Radiological control rates of retreatment and initial treatment group were 96%/95% at six months, 81%/89% at 12 months and 79%/90% at 24 months. Among 54 retreatment lesions, 13 lesions showed local control failure during follow-up. With regard to spinal cord radiation dose during SBRT, Spinal cord Pmax nBED was 46.2 Gy2/2 (retreatment) and 48.7 Gy2/2 (initial treatment). In retreatment group, total nBED to spinal cord was a mean of 83.4 Gy2/2. There was no case of radiation myelopathy detected.
  
  
  CONCLUSIONS
  Retreatment of spinal metastases using SBRT provided effective local control without neurological complications.
authors.affiliation: Department of Neurosurgery, Korean Cancer Center Hospital, Korea Institute of Radiological and Medical Science. changungkyu@yahoo.co.kr
authors.forename: Ung-Kyu
authors.initials: UK
authors.lastname: Chang
authors.forename: Won-Ik
authors.initials: WI
authors.lastname: Cho
authors.forename: Mi-Sook
authors.initials: MS
authors.lastname: Kim
authors.forename: Chul Koo
authors.initials: CK
authors.lastname: Cho
authors.forename: Dong Han
authors.initials: DH
authors.lastname: Lee
authors.forename: Chang Hun
authors.initials: CH
authors.lastname: Rhee
mesh_terms: D001943:Breast Neoplasms / Q000401:mortality / Q000473:pathology / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000401:mortality / Q000473:pathology / Q000601:surgery*; D011832:Radiation Injuries; D011836:Radiation Tolerance; D016634:Radiosurgery; D012062:Relative Biological Effectiveness; D019233:Retreatment; D012189:Retrospective Studies; D013125:Spinal Neoplasms / Q000401:mortality / Q000556:secondary* / Q000601:surgery*; D015996:Survival Rate