title: A comparative study of dose distribution of PBT, 3D-CRT and IMRT for pediatric brain tumors.
abstract: BACKGROUND
  It was reported that proton beam therapy (PBT) reduced the normal brain dose compared with X-ray therapy for pediatric brain tumors. We considered whether there was not the condition that PBT was more disadvantageous than intensity modulated photon radiotherapy (IMRT) and 3D conventional radiotherapy (3D-CRT) for treatment of pediatric brain tumors about the dose reduction for the normal brain when the tumor location or tumor size were different.
  
  
  METHODS
  The subjects were 12 patients treated with PBT at our institute, including 6 cases of ependymoma treated by local irradiation and 6 cases of germinoma treated by irradiation of all four cerebral ventricles. IMRT and 3D-CRT treatment plans were made for these 12 cases, with optimization using the same planning conditions as those for PBT. Model cases were also compared using sphere targets with different diameters or locations in the brain, and the normal brain doses with PBT, IMRT and 3D-CRT were compared using the same planning conditions.
  
  
  RESULTS
  PBT significantly reduced the average dose to normal brain tissue compared to 3D-CRT and IMRT in all cases. There was no difference between 3D-CRT and IMRT. The average normal brain doses for PBT, 3D-CRT, and IMRT were 5.1-34.8% (median 14.9%), 11.0-48.5% (23.8%), and 11.5-53.1% (23.5%), respectively, in ependymoma cases; and 42.3-61.2% (48.9%), 54.5-74.0% (62.8%), and 56.3-72.1% (61.2%), respectively, in germinoma cases. In the model cases, PBT significantly reduced the average normal brain dose for larger tumors and for tumors located at the periphery of the brain.
  
  
  CONCLUSIONS
  PBT reduces the average dose to normal brain tissue, compared with 3D-CRT and IMRT. The effect is higher for a tumor that is larger or located laterally.
authors.affiliation: Department of Radiation Oncology, University of Tsukuba, Tsukuba, Ibaraki, Japan. dtakizawa@pmrc.tsukuba.ac.jp.
authors.forename: Daichi
authors.initials: D
authors.lastname: Takizawa
authors.affiliation: Department of Radiation Oncology, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Mizumoto
authors.affiliation: Department of Neurosurgery, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Department of Radiation Oncology, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Oshiro
authors.affiliation: Department of Child Health, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Fukushima
authors.affiliation: Department of Child Health, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Fukushima
authors.affiliation: Proton Medical Research Center, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Terunuma
authors.affiliation: Department of Radiation Oncology, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Okumura
authors.affiliation: Department of Radiation Oncology, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Tsuboi
authors.affiliation: Department of Radiation Oncology, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Sakurai
mesh_terms: D000293:Adolescent; D001932:Brain Neoplasms / Q000532:radiotherapy*; D002648:Child; D002675:Child, Preschool; D004806:Ependymoma / Q000532:radiotherapy*; D005260:Female; D018237:Germinoma / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods
keywords: 3D-CRT; Brain; IMRT; PBT; Pediatric tumor