title: Hippocampal-sparing whole-brain radiotherapy: a "how-to" technique using helical tomotherapy and linear accelerator-based intensity-modulated radiotherapy.
abstract: OBJECTIVE
  Sparing the hippocampus during cranial irradiation poses important technical challenges with respect to contouring and treatment planning. Herein we report our preliminary experience with whole-brain radiotherapy using hippocampal sparing for patients with brain metastases.
  
  
  METHODS
  Five anonymous patients previously treated with whole-brain radiotherapy with hippocampal sparing were reviewed. The hippocampus was contoured, and hippocampal avoidance regions were created using a 5-mm volumetric expansion around the hippocampus. Helical tomotherapy and linear accelerator (LINAC)-based intensity-modulated radiotherapy (IMRT) treatment plans were generated for a prescription dose of 30 Gy in 10 fractions.
  
  
  RESULTS
  On average, the hippocampal avoidance volume was 3.3 cm(3), occupying 2.1% of the whole-brain planned target volume. Helical tomotherapy spared the hippocampus, with a median dose of 5.5 Gy and maximum dose of 12.8 Gy. LINAC-based IMRT spared the hippocampus, with a median dose of 7.8 Gy and maximum dose of 15.3 Gy. On a per-fraction basis, mean dose to the hippocampus (normalized to 2-Gy fractions) was reduced by 87% to 0.49 Gy(2) using helical tomotherapy and by 81% to 0.73 Gy(2) using LINAC-based IMRT. Target coverage and homogeneity was acceptable with both IMRT modalities, with differences largely attributed to more rapid dose fall-off with helical tomotherapy.
  
  
  CONCLUSIONS
  Modern IMRT techniques allow for sparing of the hippocampus with acceptable target coverage and homogeneity. Based on compelling preclinical evidence, a Phase II cooperative group trial has been developed to test the postulated neurocognitive benefit.
authors.affiliation: Department of Human Oncology, University of Wisconsin Comprehensive Cancer Center, Madison, WI 53792, USA.
authors.forename: Vinai
authors.initials: V
authors.lastname: Gondi
authors.forename: Ranjini
authors.initials: R
authors.lastname: Tolakanahalli
authors.forename: Minesh P
authors.initials: MP
authors.lastname: Mehta
authors.forename: Dinesh
authors.initials: D
authors.lastname: Tewatia
authors.forename: Howard
authors.initials: H
authors.lastname: Rowley
authors.forename: John S
authors.initials: JS
authors.lastname: Kuo
authors.forename: Deepak
authors.initials: D
authors.lastname: Khuntia
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Tomé
mesh_terms: D000679:Amygdala / Q000000981:diagnostic imaging; D001932:Brain Neoplasms / Q000532:radiotherapy / Q000556:secondary; D003072:Cognition Disorders / Q000517:prevention & control*; D016371:Cranial Irradiation / Q000379:methods*; D006624:Hippocampus / Q000166:cytology / Q000000981:diagnostic imaging / Q000528:radiation effects*; D006801:Humans; D010315:Particle Accelerators; D011832:Radiation Injuries / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013234:Stem Cells / Q000166:cytology / Q000528:radiation effects; D036542:Tomography, Spiral Computed / Q000379:methods*