title: Radiation dose-fractionation effects in spinal cord: comparison of animal and human data.
abstract: OBJECTIVE
  Recognizing spinal cord dose limits in various fractionations is essential to ensure adequate dose for tumor control while minimizing the chance of radiation-induced myelopathy (RIM). This study aimed to determine the α/β ratio of the spinal cord and the cord dose limit in terms of BED50, the biological equivalent dose (BED) that induces 50 % chance of RIM, by fitting data collected from published animal and patient studies.
  
  
  METHODS
  RIM data from five rat studies; three large animal studies on monkeys, dogs, and pigs; and 18 patient studies were included for the investigation. The α/β ratios were derived, respectively, for rat (group A), large animal (group B), patient (group C), and combined data (group D).
  
  
  RESULTS
  The α/β ratio (and its 95 % confidental interval) was 4.1 (3.2, 5.0) or 3.6 (2.6, 4.6) Gy for group A, depending on fitting algorithms. It was 3.9 (3.0, 4.8), 3.7 (2.2, 8.2) and 3.9 (3.0, 4.9) for groups B, C, and D, respectively. BED50 was 111 Gy for the combined data. It corresponds to a D50 of 73.4 Gy in 2 Gy/FX, or 19.0 Gy in single fraction. BED5, which is the BED to induce 5 % of RIM, was calculated to be 83.9 Gy. It corresponds to D5 of 55.4 Gy in 2 Gy/FX, or 16.2 Gy in single fraction.
  
  
  CONCLUSIONS
  The study showed that all four groups had similar α/β ratios close to 3.9 Gy, suggesting that the spinal cord has a similar fractionation effect for different species, including human beings.
authors.affiliation: Department of Radiation Oncology, Georgia Regents University, Augusta, GA 30912 USA.
authors.forename: Jian-Yue
authors.initials: JY
authors.lastname: Jin
authors.affiliation: Department of Radiation Oncology, Henry Ford Hospital, Detroit, MI 48202 USA.
authors.forename: Yimei
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Department of Radiation Oncology, Henry Ford Hospital, Detroit, MI 48202 USA.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Brown
authors.affiliation: Department of Radiation Oncology, Henry Ford Hospital, Detroit, MI 48202 USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Movsas
authors.affiliation: Department of Radiation Oncology, Georgia Regents University, Augusta, GA 30912 USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Kaminski
authors.affiliation: Department of Radiation Oncology, Henry Ford Hospital, Detroit, MI 48202 USA.
authors.forename: Indrin J
authors.initials: IJ
authors.lastname: Chetty
authors.affiliation: Department of Radiation Oncology, Stony Brook University, Stony Brook, NY 11794 USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Ryu
authors.affiliation: Department of Radiation Oncology, Georgia Regents University, Augusta, GA 30912 USA.
authors.forename: Feng-Ming Spring
authors.initials: FS
authors.lastname: Kong
keywords: Cord dose tolerance; Dose fractionation effect; Myelopathy; α/β ratio