title: Hippocampal sparing radiotherapy for pediatric medulloblastoma: impact of treatment margins and treatment technique.
abstract: BACKGROUND
  We investigated how varying the treatment margin and applying hippocampal sparing and proton therapy impact the risk of neurocognitive impairment in pediatric medulloblastoma patients compared with current standard 3D conformal radiotherapy.
  
  
  METHODS
  We included 17 pediatric medulloblastoma patients to represent the variability in tumor location relative to the hippocampal region. Treatment plans were generated using 3D conformal radiotherapy, hippocampal sparing intensity-modulated radiotherapy, and spot-scanned proton therapy, using 3 different treatment margins for the conformal tumor boost. Neurocognitive impairment risk was estimated based on dose-response models from pediatric CNS malignancy survivors and compared among different margins and treatment techniques.
  
  
  RESULTS
  Mean hippocampal dose and corresponding risk of cognitive impairment were decreased with decreasing treatment margins (P < .05). The largest risk reduction, however, was seen when applying hippocampal sparing proton therapy-the estimated risk of impaired task efficiency (95% confidence interval) was 92% (66%-98%), 81% (51%-95%), and 50% (30%-70%) for 3D conformal radiotherapy, intensity-modulated radiotherapy, and proton therapy, respectively, for the smallest boost margin and 98% (78%-100%), 90% (60%-98%), and 70% (39%-90%) if boosting the whole posterior fossa. Also, the distance between the closest point of the planning target volume and the center of the hippocampus can be used to predict mean hippocampal dose for a given treatment technique.
  
  
  CONCLUSIONS
  We estimate a considerable clinical benefit of hippocampal sparing radiotherapy. In choosing treatment margins, the tradeoff between margin size and risk of neurocognitive impairment quantified here should be considered.
authors: Department of Oncology, Sahlgrenska University Hospital, Gothenburg, Sweden (M.B.); Centre for Brain Repair and Rehabilitation, Institute of Neuroscience and Physiology, University of Gothenburg, Gothenburg, Sweden (M.B.); Radiation Medicine Research Center, Department of Radiation Oncology, Rigshospitalet, Copenhagen, Denmark (N.P.B., P.M.R., A.K.-B., C.H., I.R.V., S.M.B.); Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark (N.P.B., P.M.R.); Department of Clinical Physiology and Nuclear Medicine, Centre of Diagnostic Investigations, Copenhagen, Denmark (A.K.-B.); Department of Pediatric Oncology, the Queen Silvia Children's Hospital, University of Gothenburg, Gothenburg, Sweden (B.L.); Department of Human Oncology, University of Wisconsin Medical School, Madison, Wisconsin (S.M.B.); Department of Radiation Oncology, Sahlgrenska University Hospital, Gothenburg, Sweden (T.B.-E.).
authors: N Patrik
authors: NP
authors: Brodin
authors: Per
authors: P
authors: Munck af Rosenschöld
authors: Malin
authors: M
authors: Blomstrand
authors: Anne
authors: A
authors: Kiil-Berthlesen
authors: Christian
authors: C
authors: Hollensen
authors: Ivan R
authors: IR
authors: Vogelius
authors: Birgitta
authors: B
authors: Lannering
authors: Søren M
authors: SM
authors: Bentzen
authors: Thomas
authors: T
authors: Björk-Eriksson
mesh_terms: D000293:Adolescent; D002528:Cerebellar Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006624:Hippocampus; D006801:Humans; D008297:Male; D008527:Medulloblastoma / Q000473:pathology / Q000532:radiotherapy*; D059351:Organ Sparing Treatments; D058958:Organs at Risk; D011379:Prognosis; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D050397:Radiotherapy, Intensity-Modulated
keywords: cognitive risk estimation; hippocampal sparing; medulloblastoma; tumor bed boost