title: Volumetric modulated arc therapy versus step-and-shoot intensity modulated radiation therapy in the treatment of large nerve perineural spread to the skull base: a comparative dosimetric planning study.
abstract: BACKGROUND
  Cutaneous squamous cell carcinoma with large nerve perineural (LNPN) infiltration of the base of skull is a radiotherapeutic challenge given the complex target volumes to nearby organs at risk (OAR). A comparative planning study was undertaken to evaluate dosimetric differences between volumetric modulated arc therapy (VMAT) versus intensity modulated radiation therapy (IMRT) in the treatment of LNPN.
  
  
  METHODS
  Five consecutive patients previously treated with IMRT for LNPN were selected. VMAT plans were generated for each case using the same planning target volumes (PTV), dose prescriptions and OAR constraints as IMRT. Comparative parameters used to assess target volume coverage, conformity and homogeneity included V95 of the PTV (volume encompassed by the 95% isodose), conformity index (CI) and homogeneity index (HI). In addition, OAR maximum point doses, V20, V30, non-target tissue (NTT) point max doses, NTT volume above reference dose, monitor units (MU) were compared.
  
  
  RESULTS
  IMRT and VMAT plans generated were comparable for CI (P = 0.12) and HI (P = 0.89). VMAT plans achieved better V95 (P = < 0.001) and reduced V20 and V30 by 652 cubic centimetres (cc) (28.5%) and 425.7 cc (29.1%), respectively. VMAT increased MU delivered by 18% without a corresponding increase in NTT dose.
  
  
  CONCLUSIONS
  Compared with IMRT plans for LNPN, VMAT achieved comparable HI and CI.
authors.affiliation: Department of Radiation Oncology, Princess Alexandra Hospital Woolloongabba, Queensland, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Gorayski
authors.affiliation: Department of Radiation Oncology, Princess Alexandra Hospital Woolloongabba, Queensland, Australia.
authors.forename: Rhys
authors.initials: R
authors.lastname: Fitzgerald
authors.affiliation: Department of Radiation Oncology, Princess Alexandra Hospital Woolloongabba, Queensland, Australia.
authors.forename: Tamara
authors.initials: T
authors.lastname: Barry
authors.affiliation: Nursing Practice Development Unit, Princess Alexandra Hospital & Research Centre for Clinical and Community Practice Innovation, Griffith University Brisbane, Queensland, Australia.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Burmeister
authors.affiliation: Department of Radiation Oncology, Princess Alexandra Hospital Woolloongabba, Queensland, Australia ; Diamantina Institute, University of Queensland Brisbane, Queensland, Australia.
authors.forename: Matthew
authors.initials: M
authors.lastname: Foote
keywords: Base of skull; cranial nerve diseases; intensity modulated radiation therapy; skin neoplasms; squamous cell carcinoma