title: A comparison of forward and inverse treatment planning for intensity-modulated radiotherapy of head and neck cancer.
abstract: OBJECTIVE
  To compare intensity-modulated treatment plans of patients with head and neck cancer generated by forward and inverse planning.
  
  
  METHODS
  Ten intensity-modulated treatment plans, planned and treated with a step&shoot technique using a forward planning approach, were retrospectively re-planned with an inverse planning algorithm. For this purpose, two strategies were applied. First, inverse planning was performed with the same beam directions as forward planning. In addition, nine equidistant, coplanar incidences were used. The main objective of the optimisation process was the sparing of the parotid glands beside an adequate treatment of the planning target volume (PTV). Inverse planning was performed both with pencil beam and Monte Carlo dose computation to investigate the influence of dose computation on the result of the optimisation.
  
  
  RESULTS
  In most cases, both inverse planning strategies managed to improve the treatment plans distinctly due to a better target coverage, a better sparing of the parotid glands or both. A reduction of the mean dose by 3-11Gy for at least one of the parotid glands could be achieved for most of the patients. For three patients, inverse planning allowed to spare a parotid gland that had to be sacrificed by forward planning. Inverse planning increased the number of segments compared to forward planning by a factor of about 3; from 9-15 to 27-46. No significant differences for PTV and parotid glands between both inverse planning approaches were found. Also, the use of Monte Carlo instead of pencil beam dose computation did not influence the results significantly.
  
  
  CONCLUSIONS
  The results demonstrate the potential of inverse planning to improve intensity-modulated treatment plans for head and neck cases compared to forward planning while retaining clinical utility in terms of treatment time and quality assurance.
authors.affiliation: Medical Physics Division, University Hospital for Radiation Oncology, Hoppe-Seyler-Str. 3, Tübingen 72076, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Bär
authors.forename: Marco
authors.initials: M
authors.lastname: Schwarz
authors.forename: Markus
authors.initials: M
authors.lastname: Alber
authors.forename: Luc J
authors.initials: LJ
authors.lastname: Bos
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Mijnheer
authors.forename: Coen
authors.initials: C
authors.lastname: Rasch
authors.forename: Christoph
authors.initials: C
authors.lastname: Schneider
authors.forename: Fridtjof
authors.initials: F
authors.lastname: Nüsslin
authors.forename: Eugene M F
authors.initials: EM
authors.lastname: Damen
mesh_terms: D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*