title: Reirradiation with stereotactic body radiotherapy: analysis of human spinal cord tolerance using the generalized linear-quadratic model.
abstract: OBJECTIVE
  Using the generalized linear-quadratic (gLQ) model, we reanalyzed published dosimetric data from patients with radiation myelopathy (RM) after reirradiation with spinal stereotactic body radiotherapy (SBRT).
  
  
  METHODS
  Based on a published study, the thecal sac dose of five RM patients and 14 no RM patients were reanalyzed using gLQ model. Maximum point doses (Pmax) in the thecal sac were obtained. The gLQ-based biological effective doses were calculated and normalized (nBEDgLQ) to a 2-Gy equivalent dose (nBEDgLQ = Gy2/2_gLQ). The initial conventional radiotherapy dose, converted to Gy2/2_gLQ, was added.
  
  
  RESULTS
  Total (conventional radiotherapy + SBRT) mean Pmax nBEDgLQ was lower in no RM than RM patients: 59.2 Gy2/2_gLQ (range: 37.5-101.9) versus 94.8 Gy2/2_gLQ (range: 70.2-133.4) (p = 0.0016). The proportion of total Pmax nBEDgLQ accounted for by the SBRT Pmax nBEDgLQ was higher for RM patients. No RMs were seen below a total spinal cord nBEDgLQ of 70 Gy2/2_gLQ.
  
  
  CONCLUSIONS
  The gLQ-derived spinal cord tolerance for total nBEDgLQ was 70 Gy2/2_gLQ.
authors.affiliation: Department of Radiation Oncology, East Carolina University, Greenville, NC, USA.
authors.forename: Zhibin
authors.initials: Z
authors.lastname: Huang
authors.forename: Nina A
authors.initials: NA
authors.lastname: Mayr
authors.forename: William T
authors.initials: WT
authors.lastname: Yuh
authors.forename: Jian Z
authors.initials: JZ
authors.lastname: Wang
authors.forename: Simon S
authors.initials: SS
authors.lastname: Lo
mesh_terms: D000016:Abnormalities, Radiation-Induced / Q000473:pathology / Q000628:therapy*; D000293:Adolescent; D000328:Adult; D000368:Aged; D006801:Humans; D016014:Linear Models; D008875:Middle Aged; D011829:Radiation Dosage; D011836:Radiation Tolerance; D016634:Radiosurgery; D019233:Retreatment; D013116:Spinal Cord / Q000473:pathology / Q000528:radiation effects; D013118:Spinal Cord Diseases / Q000473:pathology / Q000628:therapy*; D013125:Spinal Neoplasms / Q000473:pathology / Q000532:radiotherapy*