title: Estimation of optimal margin for intrafraction movements during frameless brain radiosurgery.
abstract: OBJECTIVE
  To examine the dosimetric effect of intrafraction movements occurred during image-guided frameless brain radiosurgery and to derive the optimal margin recipe to compensate the movement.
  
  
  METHODS
  The patients' movements during image-guided radiosurgeries were measured using skull-tracking method incorporated in the CyberKnife system. The dosimetric changes with the movements were computed using the six different dynamic-arc treatment plans based on the dose-grid analysis method. The authors extensively searched the proper relationship between the dose variations and the intrafraction geometric errors. The optimal margin for intrafraction movement was estimated via statistical analysis of the dosimetric changes with 262 actual patients' data.
  
  
  RESULTS
  The overall geometric effect of intrafraction movements was approximated as 1.0 r+0.2σ, where r and σ are the average and standard deviation of the movements, respectively. The authors computed the required margins to compensate the movements with various confidence levels and with various estimated times for completing the treatments. The computed optimal margins were calculated as 2.1, 3.2, and 4.2 mm at 90% confidence level when the authors assumed the estimated treatment times of 10, 20, and 30 min, respectively.
  
  
  CONCLUSIONS
  The authors provide a quantitative relationship for dosimetric change with the intrafraction movement and derived appropriate margin recipes to ensure the prescribed dose delivery to targeted area for frameless brain radiosurgery.
authors: Department of Radiation Oncology, School of Medicine and Institute of Health Science, Gyeongsang National University, Jinju 660-702, South Korea.
authors: Ki Mun
authors: KM
authors: Kang
authors: Gyu Young
authors: GY
authors: Chai
authors: Bae Kwon
authors: BK
authors: Jeong
authors: In-Bong
authors: IB
authors: Ha
authors: Sangbong
authors: S
authors: Lee
authors: Kyung Bum
authors: KB
authors: Park
authors: Jin-Myung
authors: JM
authors: Jung
authors: Young Kyung
authors: YK
authors: Lim
authors: Seung Hoon
authors: SH
authors: Yoo
authors: Hojin
authors: H
authors: Jeong
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging*; D019583:Dose Fractionation, Radiation; D006801:Humans; D009068:Movement; D011859:Radiography; D011874:Radiometry; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013997:Time Factors