title: Robust Intensity Modulated Proton Therapy (IMPT) Increases Estimated Clinical Benefit in Head and Neck Cancer Patients.
abstract: OBJECTIVE
  To compare the clinical benefit of robust optimized Intensity Modulated Proton Therapy (minimax IMPT) with current photon Intensity Modulated Radiation Therapy (IMRT) and PTV-based IMPT for head and neck cancer (HNC) patients. The clinical benefit is quantified in terms of both Normal Tissue Complication Probability (NTCP) and target coverage in the case of setup and range errors.
  
  
  METHODS
  For 10 HNC patients, PTV-based IMRT (7 fields), minimax and PTV-based IMPT (2, 3, 4, 5 and 7 fields) plans were tested on robustness. Robust optimized plans differed from PTV-based plans in that they target the CTV and penalize possible error scenarios, instead of using the static isotropic CTV-PTV margin. Perturbed dose distributions of all plans were acquired by simulating in total 8060 setup (±3.5 mm) and range error (±3%) combinations. NTCP models for xerostomia and dysphagia were used to predict the clinical benefit of IMPT versus IMRT.
  
  
  RESULTS
  The robustness criterion was met in the IMRT and minimax IMPT plans in all error scenarios, but this was only the case in 1 of 40 PTV-based IMPT plans. Seven (out of 10) patients had relatively large NTCP reductions in minimax IMPT plans compared to IMRT. For these patients, xerostomia and dysphagia NTCP values were reduced by 17.0% (95% CI; 13.0-21.1) and 8.1% (95% CI; 4.9-11.2) on average with minimax IMPT. Increasing the number of fields did not contribute to plan robustness, but improved organ sparing.
  
  
  CONCLUSIONS
  The estimated clinical benefit in terms of NTCP of robust optimized (minimax) IMPT is greater than that of IMRT and PTV-based IMPT in HNC patients. Furthermore, the target coverage of minimax IMPT plans in the presence of errors was comparable to IMRT plans.
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.|Institute for Biomedical Technology and Technical Medicine (MIRA), University of Twente, Enschede, The Netherlands.
authors.forename: Lisanne V
authors.initials: LV
authors.lastname: van Dijk
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Roel J H M
authors.initials: RJ
authors.lastname: Steenbakkers
authors.affiliation: Institute for Biomedical Technology and Technical Medicine (MIRA), University of Twente, Enschede, The Netherlands.
authors.forename: Bennie
authors.initials: B
authors.lastname: ten Haken
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Hans Paul
authors.initials: HP
authors.lastname: van der Laan
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Aart A
authors.initials: AA
authors.lastname: van 't Veld
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Langendijk
authors.affiliation: Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Erik W
authors.initials: EW
authors.lastname: Korevaar
mesh_terms: D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D061766:Proton Therapy; D011832:Radiation Injuries / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D016896:Treatment Outcome