title: The price of robustness; impact of worst-case optimization on organ-at-risk dose and complication probability in intensity-modulated proton therapy for oropharyngeal cancer patients.
abstract: To quantify the impact of the degree of robustness against setup errors and range errors on organ-at-risk (OAR) dose and normal tissue complication probabilities (NTCPs) in intensity-modulated proton therapy for oropharyngeal cancer patients.
  
  
  
  For 20 oropharyngeal cases (10 unilateral and 10 bilateral), robust treatment plans were generated using 'minimax' worst-case optimization. We varied the robustness against setup errors ('setup robustness') from 1 to 7mm and the robustness against range errors ('range robustness') from 1% to 7% (+1mm). We evaluated OAR doses and NTCP-values for xerostomia, dysphagia and larynx edema.
  
  
  
  Varying the degree of setup robustness was found to have a considerably larger impact than varying the range robustness. Increasing setup robustness from 1mm to 3, 5, and 7mm resulted in average NTCP-values to increase by 1.9, 4.4 and 7.5 percentage point, whereas they increased by only 0.4, 0.8 and 1.2 percentage point when increasing range robustness from 1% to 3%, 5% and 7%. The degree of setup robustness was observed to have a clinically significant impact in bilateral cases in particular.
  
  
  
  For oropharyngeal cancer patients, minimizing setup errors should be given a higher priority than minimizing range errors.
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands. Electronic address: s.vandewater@hollandptc.nl.
authors.forename: Steven
authors.initials: S
authors.lastname: van de Water
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands; Delft University of Technology, Faculty of Applied Sciences, Section Radiation Detection and Medical Imaging, The Netherlands.
authors.forename: Iris
authors.initials: I
authors.lastname: van Dam
authors.affiliation: Delft University of Technology, Faculty of Applied Sciences, Section Radiation Detection and Medical Imaging, The Netherlands.
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Schaart
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands.
authors.forename: Abrahim
authors.initials: A
authors.lastname: Al-Mamgani
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands.
authors.forename: Ben J M
authors.initials: BJ
authors.lastname: Heijmen
authors.affiliation: Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands.
authors.forename: Mischa S
authors.initials: MS
authors.lastname: Hoogeman
mesh_terms: D006801:Humans; D058958:Organs at Risk; D009959:Oropharyngeal Neoplasms / Q000532:radiotherapy*; D011336:Probability; D061766:Proton Therapy / Q000009:adverse effects*; D011832:Radiation Injuries / Q000209:etiology*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D014987:Xerostomia / Q000209:etiology
keywords: Head-and-neck cancer; IMPT; Oropharyngeal cancer; Proton therapy; Robust optimization