title: Tolerance of pyramidal tract to gamma knife radiosurgery based on diffusion-tensor tractography.
abstract: OBJECTIVE
  To minimize the morbidity of radiosurgery for critically located lesions, we integrated diffusion-tensor tractography into treatment planning for gamma-knife radiosurgery. We calculated the refined tolerance of the pyramidal tract (PT) after prospective application of the technique to additional patients.
  
  
  METHODS
  The relationship between the dosimetry during treatment planning and the development of subsequent motor complications was investigated in 24 patients, 9 studied retrospectively and 15 studied prospectively. The maximal dose to the PT and the volumes of the PT that received > or = 20 Gy (20-Gy volume) and > or = 25 Gy (25-Gy volume) were calculated. Univariate logistic regression analyses were used to produce dose-response curves. Differences in the tolerable dose according to the PT location were calculated.
  
  
  RESULTS
  Univariate logistic regression analysis of the motor complications revealed a significant independent correlation with the maximal dose to the PT and the 20- and 25-Gy volumes. The maximal dose to the PT with a 5% risk of motor complications was 23 Gy compared with 15 Gy in our previous report. The risk of motor complications was significantly greater in the internal capsule than in the corona radiata for the 20- and 25-Gy volumes in generalized Wilcoxon tests (p = 0.031), although no significant difference was observed for the maximal dose.
  
  
  CONCLUSIONS
  The tolerable dose of the PT was greater than that previously reported. The internal capsule was more sensitive to high-dose irradiation over a wide area of the PT, probably owing to the dense concentration of motor fibers.
authors.affiliation: Department of Neurosurgery, University of Tokyo Hospital, Tokyo, Japan. kskmaru-tky@umin.ac.jp
authors.forename: Keisuke
authors.initials: K
authors.lastname: Maruyama
authors.forename: Kyousuke
authors.initials: K
authors.lastname: Kamada
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ota
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Koga
authors.forename: Daisuke
authors.initials: D
authors.lastname: Itoh
authors.forename: Kenji
authors.initials: K
authors.lastname: Ino
authors.forename: Shigeki
authors.initials: S
authors.lastname: Aoki
authors.forename: Masao
authors.initials: M
authors.lastname: Tago
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Masutani
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shin
authors.forename: Nobuhito
authors.initials: N
authors.lastname: Saito
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011712:Pyramidal Tracts / Q000503:physiopathology / Q000528:radiation effects*; D011836:Radiation Tolerance; D016634:Radiosurgery / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D012189:Retrospective Studies