title: Dosimetric comparison of absolute and relative dose distributions between tissue maximum ratio and convolution algorithms for acoustic neurinoma plans in Gamma Knife radiosurgery.
abstract: BACKGROUND
  The treatment planning for Gamma Knife (GK) stereotactic radiosurgery (SRS) that performs dose calculations based on tissue maximum ratio (TMR) algorithm has disadvantages in predicting dose in tissue heterogeneity. The latest version of the planning software is equipped with a convolution dose algorithm as an optional extra and the new algorithm is able to compensate for head inhomogeneity. However, the effect of this improved calculation method requires detailed validation in clinical cases. In this study, we compared absolute and relative dose distributions of treatment plans for acoustic neurinoma between TMR and the convolution calculation.
  
  
  METHODS
  Twenty-nine clinically used plans created by TMR algorithm were recalculated by convolution method. Differences between TMR and convolution were evaluated in terms of absolute dose (beam-on time), dosimetric parameters including target coverage, selectivity, conformity index, gradient index, radical homogeneity index and the dose-volume relationship.
  
  
  RESULTS
  The discrepancy in estimated absolute dose to the target ranged from 1 to 7 % between TMR and convolution. In addition, dosimetric parameters of the two methods achieved statistical significance. However, it was difficult to see the change of relative dose distribution by visual assessment on a monitor.
  
  
  CONCLUSIONS
  Convolution, heterogeneity correction calculation, and the algorithm are necessary to reduce the dosimetric uncertainty of each case in GK SRS.
authors.affiliation: Department of Radiological Sciences, Nagoya University Graduate School of Medicine, 1-1-20 Daikominami, Higashiku, Nagoya, Aichi, 461-8673, Japan, hnakazawa@kaikou.or.jp.
authors.forename: Hisato
authors.initials: H
authors.lastname: Nakazawa
authors.forename: Masataka
authors.initials: M
authors.lastname: Komori
authors.forename: Yuta
authors.initials: Y
authors.lastname: Shibamoto
authors.forename: Takahiko
authors.initials: T
authors.lastname: Tsugawa
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Mori
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Kobayashi
mesh_terms: D000465:Algorithms; D006801:Humans; D009010:Monte Carlo Method; D009464:Neuroma, Acoustic / Q000601:surgery*; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted