title: Clinical applicability of biologically effective dose calculation for spinal cord in fractionated spine stereotactic body radiation therapy.
abstract: BACKGROUND
  The aim of the study was to investigate whether biologically effective dose (BED) based on linear-quadratic model can be used to estimate spinal cord tolerance dose in spine stereotactic body radiation therapy (SBRT) delivered in 4 or more fractions.
  
  
  METHODS
  Sixty-three metastatic spinal lesions in 47 patients were retrospectively evaluated. The most frequently prescribed dose was 36 Gy in 4 fractions. In planning, we tried to limit the maximum dose to the spinal cord or cauda equina less than 50% of prescription or 45 Gy2/2. BED was calculated using maximum point dose of spinal cord.
  
  
  RESULTS
  Maximum spinal cord dose per fraction ranged from 2.6 to 6.0 Gy (median 4.3 Gy). Except 4 patients with 52.7, 56.4, 62.4, and 67.9 Gy2/2, equivalent total dose in 2-Gy fraction of the patients was not more than 50 Gy2/2 (12.1-67.9, median 32.0). The ratio of maximum spinal cord dose to prescription dose increased up to 82.2% of prescription dose as epidural spinal cord compression grade increased. No patient developed grade 2 or higher radiation-induced spinal cord toxicity during follow-up period of 0.5 to 53.9 months.
  
  
  CONCLUSIONS
  In fractionated spine SBRT, BED can be used to estimate spinal cord tolerance dose, provided that the dose per fraction to the spinal cord is moderate, e.g. < 6.0 Gy. It appears that a maximum dose of up to 45-50 Gy2/2 to the spinal cord is tolerable in 4 or more fractionation regimen.
authors.affiliation: Department of Radiation Oncology; Gachon University Gil Medical Center, Republic of Korea.
authors.forename: Seung Heon
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology; Gachon University Gil Medical Center, Republic of Korea.
authors.forename: Kyu Chan
authors.initials: KC
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology; Gachon University Gil Medical Center, Republic of Korea.
authors.forename: Jinho
authors.initials: J
authors.lastname: Choi
authors.affiliation: Department of Radiation Oncology; Gachon University Gil Medical Center, Republic of Korea.
authors.forename: So Hyun
authors.initials: SH
authors.lastname: Ahn
authors.affiliation: Department of Radiation Oncology; Gachon University Gil Medical Center, Republic of Korea.
authors.forename: Seok Ho
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology; Gachon University Gil Medical Center, Republic of Korea.
authors.forename: Ki Hoon
authors.initials: KH
authors.lastname: Sung
authors.affiliation: Gachon Medical Research Institute, Gachon University Gil Medical Center, Republic of Korea.
authors.forename: Se Hee
authors.initials: SH
authors.lastname: Kil
keywords: biologically effective dose; linear quadratic model; spinal cord; spine stereotactic body radiation therapy; tolerance dose