title: Dose specification for hippocampal sparing whole brain radiotherapy (HS WBRT): considerations from the UK HIPPO trial QA programme.
abstract: OBJECTIVE
  The HIPPO trial is a UK randomized Phase II trial of hippocampal sparing (HS) vs conventional whole-brain radiotherapy after surgical resection or radiosurgery in patients with favourable prognosis with 1-4 brain metastases. Each participating centre completed a planning benchmark case as part of the dedicated radiotherapy trials quality assurance programme (RTQA), promoting the safe and effective delivery of HS intensity-modulated radiotherapy (IMRT) in a multicentre trial setting.
  
  
  METHODS
  Submitted planning benchmark cases were reviewed using visualization for radiotherapy software (VODCA) evaluating plan quality and compliance in relation to the HIPPO radiotherapy planning and delivery guidelines.
  
  
  RESULTS
  Comparison of the planning benchmark data highlighted a plan specified using dose to medium as an outlier by comparison with those specified using dose to water. Further evaluation identified that the reported plan statistics for dose to medium were lower as a result of the dose calculated at regions of PTV inclusive of bony cranium being lower relative to brain.
  
  
  CONCLUSIONS
  Specification of dose to water or medium remains a source of potential ambiguity and it is essential that as part of a multicentre trial, consideration is given to reported differences, particularly in the presence of bone. Evaluation of planning benchmark data as part of an RTQA programme has highlighted an important feature of HS IMRT dosimetry dependent on dose being specified to water or medium, informing the development and undertaking of HS IMRT as part of the HIPPO trial. Advances in knowledge: The potential clinical impact of differences between dose to medium and dose to water are demonstrated for the first time, in the setting of HS whole-brain radiotherapy.
authors.affiliation: 1 National Radiotherapy Trials Quality Assurance Group (RTTQA), Mount Vernon Hospital, London, UK.
authors.forename: Daniel
authors.identifier: http://orcid.org/0000-0001-8622-9671
authors.initials: D
authors.lastname: Megias
authors.affiliation: 2 Cancer Research UK and University College London Cancer Trials Centre, London, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Phillips
authors.affiliation: 2 Cancer Research UK and University College London Cancer Trials Centre, London, UK.
authors.forename: Laura
authors.initials: L
authors.lastname: Clifton-Hadley
authors.affiliation: 3 Nottingham University Hospitals NHS Trust, Nottingham City Hospital, Nottingham, UK.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Harron
authors.affiliation: 1 National Radiotherapy Trials Quality Assurance Group (RTTQA), Mount Vernon Hospital, London, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Eaton
authors.affiliation: 4 Queen Elizabeth Hospital, Hall Edwards Radiotherapy Research Group, Birmingham, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Sanghera
authors.affiliation: 5 University of Manchester, Manchester Cancer Research Centre, Manchester Academic Health Science Centre, Christie NHS Foundation Trust, Manchester, UK.
authors.forename: Gillian
authors.initials: G
authors.lastname: Whitfield
mesh_terms: D001932:Brain Neoplasms / Q000532:radiotherapy*; D006624:Hippocampus / Q000528:radiation effects*; D006801:Humans; D059351:Organ Sparing Treatments / Q000379:methods*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D006113:United Kingdom