title: Does 4 MV perform better compared to 6 MV in the presence of air cavities in the head and neck region?
abstract: OBJECTIVE
  The underdose near air cavities in the head and neck region at photon energies of 4 MV and 6 MV was studied in search for clinical advantages of the 4 MV over 6 MV treatments.
  
  
  METHODS
  The on-axis and off-axis dose distributions were measured with a parallel-plate ionization chamber and films in polystyrene phantoms containing an air cavity of appropriate size based on the results of computed tomography scans.
  
  
  RESULTS
  Although most results are similar for both energies, the 4 MV photon beams give a somewhat smaller underdose effect and a faster re-build up than the 6 MV. For both energies a significant underdose effect was observed at the edge of the field in the larynx phantom. This proved to be true for small and large fields, for smaller and larger cavities, for one-beam as well as parallel-opposed beams.
  
  
  CONCLUSIONS
  For most clinically relevant situations there is no remarkable benefit in the use of either of the two energies.
authors.affiliation: Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Petoukhova
authors.forename: Chris H J
authors.initials: CH
authors.lastname: Terhaard
authors.forename: Hans
authors.initials: H
authors.lastname: Welleweerd
mesh_terms: D000388:Air; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007830:Larynx / Q000033:anatomy & histology; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy