title: Evaluation of hippocampus dose for patients undergoing intensity-modulated radiotherapy for nasopharyngeal carcinoma.
abstract: OBJECTIVE
  To evaluate the dose received by the hippocampus among patients undergoing intensity-modulated radiotherapy (IMRT) for nasopharyngeal cancer.
  
  
  METHODS
  10 patients with biopsy-proven, locally advanced nasopharyngeal cancer constituted the study population. The total prescribed dose to the planning target volume (PTV) was 70 Gy (D95%) delivered in 2.12-Gy daily fractions using IMRT. Using established anatomical guidelines, MRI co-registration and the assistance of a board-certified neuroradiologist, the right and left hippocampi were delineated on axial imaging from the CT scan obtained at simulation for each patient beginning at the most anterior portion of the lateral ventricle. IMRT treatment plans were generated without dose-volume constraints to the hippocampus. A range of dose-volume statistics was calculated.
  
  
  RESULTS
  The mean hippocampus volume was 6.01 ± 2.61 cm(3). The mean V20 was 72.2%; V40 was 22.0%; V50 was 10.2%; and V60 was 5.5%. The average mean, minimum and maximum hippocampus doses were 30.27 Gy (range, 19.08-47.99 Gy); 17.54 Gy (range, 11.66-33.17 Gy); and 54.95 Gy (range, 35.59-75.57 Gy), respectively. The hippocampus received a maximum dose exceeding 70 Gy in 30% of cases.
  
  
  CONCLUSIONS
  Our dosimetric analysis suggests that, for patients undergoing IMRT for nasopharyngeal cancer, the hippocampus routinely receives significantly high doses.
  
  
  CONCLUSIONS
  The hippocampus receives a fair amount of incidental radiation during treatment for nasopharyngeal cancer. Given the importance of this structure with respect to memory and neurocognitive function, consideration should be given to identifying the hippocampus as a critical organ at risk in the IMRT optimization process.
authors.affiliation: Department of Radiation Oncology, University of California Davis Comprehensive Cancer Center, Sacramento, CA, USA.
authors.forename: B
authors.initials: B
authors.lastname: Khodayari
authors.forename: A L
authors.initials: AL
authors.lastname: Michaud
authors.forename: S
authors.initials: S
authors.lastname: Stanic
authors.forename: O H
authors.initials: OH
authors.lastname: Wooten
authors.forename: A
authors.initials: A
authors.lastname: Dublin
authors.forename: J A
authors.initials: JA
authors.lastname: Purdy
authors.forename: A M
authors.initials: AM
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D002277:Carcinoma; D005260:Female; D006624:Hippocampus / Q000528:radiation effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D058958:Organs at Risk / Q000528:radiation effects; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed