title: Evaluating the dosimetric effect of treatment-induced changes in virally mediated head and neck cancer patients.
abstract: BACKGROUND
  Patients with virally mediated head and neck cancer (VMHNC) often present with advanced nodal disease that is highly radioresponsive as demonstrated by tumour and nodal regression during treatment. The resultant changes may impact on the planned dose distribution and so adversely affect the therapeutic ratio. The aim of this study was to evaluate the dosimetric effect of treatment-induced anatomical changes in VMHNC patients who had undergone a replan.
  
  
  METHODS
  Thirteen patients with virally mediated oropharyngeal or nasopharyngeal cancer who presented for definitive radiotherapy between 2005 and 2010 and who had a replan generated were investigated. The dosimetric effect of anatomical changes was quantified by comparing dose-volume histograms (DVH) of primary and nodal gross target volumes and organs at risk (OAR), including spinal cord and parotid glands, from the original plan and a comparison plan.
  
  
  RESULTS
  Eleven three-dimensional conformal radiation therapy (3DCRT) and two intensity modulated radiation therapy (IMRT) plans were evaluated. Dose to the spinal cord and brainstem increased by 4.1% and 2.6%, respectively. Mean dose to the parotid glands also increased by 3.5%. In contrast, the dose received by 98% of the primary and nodal gross tumour volumes decreased by 0.15% and 0.3%, respectively, when comparing the initial treatment plan to the comparison plan.
  
  
  CONCLUSIONS
  In this study, treatment-induced anatomical changes had the greatest impact on OAR dose with negligible effect on the dose to nodal gross tumour volumes. In the era of IMRT, accounting for treatment-induced anatomical changes is important as focus is placed on minimizing the acute and long-term side effects of treatment.
authors.affiliation: Radiation Oncology Department, Princess Alexandra Hospital Brisbane, Queensland, Australia ; Queensland University of Technology Brisbane, Queensland, Australia.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Brown
authors.affiliation: Radiation Oncology Department, Radiation Oncology Mater Centre Brisbane, Queensland, Australia.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Owen
authors.affiliation: Queensland University of Technology Brisbane, Queensland, Australia.
authors.forename: Kerrie
authors.initials: K
authors.lastname: Mengersen
authors.affiliation: Queensland University of Technology Brisbane, Queensland, Australia.
authors.forename: Fiona
authors.initials: F
authors.lastname: Harden
authors.affiliation: Radiation Oncology Department, Princess Alexandra Hospital Brisbane, Queensland, Australia ; School of Medicine, University of Queensland Brisbane, Queensland, Australia.
authors.forename: Sandro
authors.initials: S
authors.lastname: Porceddu
keywords: HPV-16; Head and neck cancer; planning; radiation therapy