title: Quantitative assessment of inter-clinician variability of target volume delineation for medulloblastoma: quality assurance for the SIOP PNET 4 trial protocol.
abstract: OBJECTIVE
  To assess inter-clinician variability amongst specialist paediatric radiation oncologists in delineating clinical target volumes for treating medulloblastoma as a quality assurance exercise prior to the introduction of the SIOP PNET 4 trial protocol of conformal radiotherapy to the posterior fossa and tumour bed.
  
  
  METHODS
  Participants from 17 UK centres attended an educational meeting and then completed a clinical planning exercise to outline: (1) the whole posterior fossa and (2) the tumour bed. Quantitative analysis of the volumes, lengths, spatial positioning and axial planes for each individual was carried out and variation between individuals analysed.
  
  
  RESULTS
  Outlining of the posterior fossa was reasonably consistent, although most variation was seen in defining the superior border of the tentorium. A major difference was the decision whether or not to include the post-surgical meningocoele in the clinical target volume (CTV). The CTV for the tumour bed was under treated by all participants due to lack of inclusion of pre-operative tumour extent.
  
  
  CONCLUSIONS
  This exercise demonstrated several ambiguities in the draft protocol and highlighted particular areas of inter-clinician variation. Consequently the protocol was revised and improved to take account of these findings. We recommend that planning exercises, in conjunction with education and training, should be implemented before the start of any new radiotherapy trial. In the future, the use of image transfer will allow prospective peer review of target volumes before treatment commences. These measures are essential to ensure that alterations in clinical practice are achieved in a uniform way.
authors.affiliation: Oncology Centre, Addenbrooke's Hospital, Box 193, Hills Road, Cambridge CB2 2QQ, UK.
authors.forename: Charlotte E
authors.initials: CE
authors.lastname: Coles
authors.forename: Andrew C F
authors.initials: AC
authors.lastname: Hoole
authors.forename: Susan V
authors.initials: SV
authors.lastname: Harden
authors.forename: Neil G
authors.initials: NG
authors.lastname: Burnet
authors.forename: Nicola
authors.initials: N
authors.lastname: Twyman
authors.forename: Roger E
authors.initials: RE
authors.lastname: Taylor
authors.forename: Rolf D
authors.initials: RD
authors.lastname: Kortmann
authors.forename: Michael V
authors.initials: MV
authors.lastname: Williams
mesh_terms: D002528:Cerebellar Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D002648:Child; D006801:Humans; D008279:Magnetic Resonance Imaging; D008527:Medulloblastoma / Q000175:diagnosis / Q000532:radiotherapy*; D015337:Multicenter Studies as Topic; D015588:Observer Variation; D011785:Quality Assurance, Health Care; D011829:Radiation Dosage; D020266:Radiotherapy, Conformal / Q000592:standards*; D016032:Randomized Controlled Trials as Topic / Q000592:standards