title: Parotid gland sparing effect by computed tomography-based modified lower field margin in whole brain radiotherapy.
abstract: OBJECTIVE
  Parotid gland can be considered as a risk organ in whole brain radiotherapy (WBRT). The purpose of this study is to evaluate the parotid gland sparing effect of computed tomography (CT)-based WBRT compared to 2-dimensional plan with conventional field margin.
  
  
  METHODS
  From January 2008 to April 2011, 53 patients underwent WBRT using CT-based simulation. Bilateral two-field arrangement was used and the prescribed dose was 30 Gy in 10 fractions. We compared the parotid dose between 2 radiotherapy plans using different lower field margins: conventional field to the lower level of the atlas (CF) and modified field fitted to the brain tissue (MF).
  
  
  RESULTS
  Averages of mean parotid dose of the 2 protocols with CF and MF were 17.4 Gy and 8.7 Gy, respectively (p < 0.001). Mean parotid dose of both glands ≥20 Gy were observed in 15 (28.3%) for CF and in 0 (0.0%) for MF. The whole brain percentage volumes receiving >98% of prescribed dose were 99.7% for CF and 99.5% for MF.
  
  
  CONCLUSIONS
  Compared to WBRT with CF, CT-based lower field margin modification is a simple and effective technique for sparing the parotid gland, while providing similar dose coverage of the whole brain.
authors.affiliation: Department of Radiation Oncology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Oyeon
authors.initials: O
authors.lastname: Cho
authors.forename: Mison
authors.initials: M
authors.lastname: Chun
authors.forename: Sung Ho
authors.initials: SH
authors.lastname: Park
authors.forename: Young-Taek
authors.initials: YT
authors.lastname: Oh
authors.forename: Mi-Hwa
authors.initials: MH
authors.lastname: Kim
authors.forename: Hae-Jin
authors.initials: HJ
authors.lastname: Park
authors.forename: Sang Soo
authors.initials: SS
authors.lastname: Nam
authors.forename: Jaesung
authors.initials: J
authors.lastname: Heo
authors.forename: O Kyu
authors.initials: OK
authors.lastname: Noh
keywords: Normal tissue complication probability; Parotid gland sparing; Whole brain radiotherapy; Xerostomia