title: Proton Radiotherapy for Midline Central Nervous System Lesions: A Class Solution.
abstract: OBJECTIVE
  Midline and central lesions of the brain requiring conventional radiotherapy (RT) present complex difficulties in dose avoidance to organs at risk (OAR). In either definitive or adjuvant settings, proper RT coverage of these lesions involves unnecessary treatment of large volumes of normal brain. We propose a class solution for these lesions using proton radiotherapy (PrT).
  
  
  METHODS
  The records of the Indiana University Health Proton Therapy Center were reviewed for patients presenting between January 1, 2005 and October 1, 2013 with midline central nervous system (CNS) lesions. Twenty-four patients were identified. After Institutional Review Board approval was granted, their dosimetry was reviewed for target volume doses and OAR dose avoidance.
  
  
  RESULTS
  For these cases, meningiomas were the most common histology (8 cases), and next most prevalent were craniopharyngiomas (6 cases). The others were various different deep midline brain tumors (10 cases). In all cases, fields formed by vertex and/or anterior/posterior superior oblique PrT beams along the midsagittal plane were used to provide coverage with minimal dose to the brain stem or to the cerebral hemispheres. The median prescribed dose to the planning target volume for treating these patients was 54.0 Gy RBE (range 48.6-62.5) with a mean dose of 53.5 Gy RBE. The average of the mean doses to the brain stems using these fields in the 24 plans was 18.4 Gy RBE (range 0.0-44.7). Similarly, the average of the mean doses to the hippocampi was 15.8 Gy RBE (range 0.0-52.6).
  
  
  CONCLUSIONS
  We consider these patients to be optimally treated with PrT. The use of modified midsagittal PrT schemas allows for the treatment of midline CNS lesions with sparing of most of the uninvolved brain.
authors.affiliation: Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, Ind., USA.
authors.forename: Neil C
authors.initials: NC
authors.lastname: Estabrook
authors.forename: Mark W
authors.initials: MW
authors.lastname: McDonald
authors.forename: Ted A
authors.initials: TA
authors.lastname: Hoene
authors.forename: Greg K
authors.initials: GK
authors.lastname: Bartlett
authors.forename: Peter A S
authors.initials: PA
authors.lastname: Johnstone
authors.forename: Kevin P
authors.initials: KP
authors.lastname: McMullen
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Buchsbaum
mesh_terms: D001932:Brain Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D002490:Central Nervous System / Q000473:pathology* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D058958:Organs at Risk; D061766:Proton Therapy / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods