title: Improvement of therapeutic index for brain tumors with daily image guidance.
abstract: BACKGROUND
  Image-guidance maximizes the therapeutic index of brain irradiation by decreasing setup uncertainty. As dose-volume data emerge defining the tolerance of critical normal structures responsible for neuroendocrine function and neurocognition, minimizing clinical target volume (CTV) to planning target volume (PTV) expansion of targets near these structures potentially lessens long-term toxicity.
  
  
  METHODS
  We reviewed the treatment records of 29 patients with brain tumors, with a total of 517 fractions analyzed. The CTV was uniformly expanded by 3 mm to create the PTV for all cases. We determined the effect of patient specific factors (prescribed medications, weight gain, tumor location) and image-guidance technique on setup uncertainty and plotted the mean +/- standard deviation for each factor. ANOVA was used to determine significance between these factors on setup uncertainty. We determined the impact of applying the initial three fraction variation as custom PTV-expansion on dose to normal structures.
  
  
  RESULTS
  The initial 3 mm margin encompassed 88% of all measured shifts from daily imaging for all fractions. There was no difference (p = n.s.) in average setup uncertainty between CBCT or kV imaging for all patients. Vertical, lateral, longitudinal, and 3D shifts were similar (p = n.s.) between days 1, 2, and 3 imaging and later fractions. Patients prescribed sedatives experienced increased setup uncertainty (p < 0.05), while weight gain, corticosteroid administration, and anti-seizure medication did not associate with increased setup uncertainty. Patients with targets near OAR with individualized margins led to decreased OAR dose. No reductions to targets occurred with individualized PTVs.
  
  
  CONCLUSIONS
  Daily imaging allows application of individualized CTV expansion to reduce dose to OAR responsible for neurocognition, learning, and neuroendocrine function below doses shown to correlate with long-term morbidity. The demonstrated reduction in dose to OAR in this study has implications for quality of life and provides the motivation to pursue custom PTV expansion.
authors.forename: Lisa Be
authors.initials: LB
authors.lastname: Shields
authors.forename: James M
authors.initials: JM
authors.lastname: Coons
authors.forename: Catherine
authors.initials: C
authors.lastname: Dedich
authors.forename: Maria
authors.initials: M
authors.lastname: Ragains
authors.forename: Kristi
authors.initials: K
authors.lastname: Scalf
authors.forename: Todd W
authors.initials: TW
authors.lastname: Vitaz
authors.affiliation: The Brain Tumor Center, Norton Healthcare, Louisville, KY, USA. acspalding1@gmail.com.
authors.forename: Aaron C
authors.initials: AC
authors.lastname: Spalding
mesh_terms: D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography; D005910:Glioma / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008579:Meningioma / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D058958:Organs at Risk; D019047:Phantoms, Imaging; D010911:Pituitary Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011788:Quality of Life; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted