title: Comparison of organ-at-risk sparing and plan robustness for spot-scanning proton therapy and volumetric modulated arc photon therapy in head-and-neck cancer.
abstract: OBJECTIVE
  Proton radiotherapy for head-and-neck cancer (HNC) aims to improve organ-at-risk (OAR) sparing over photon radiotherapy. However, it may be less robust for setup and range uncertainties. The authors investigated OAR sparing and plan robustness for spot-scanning proton planning techniques and compared these with volumetric modulated arc therapy (VMAT) photon plans.
  
  
  METHODS
  Ten HNC patients were replanned using two arc VMAT (RapidArc) and spot-scanning proton techniques. OARs to be spared included the contra- and ipsilateral parotid and submandibular glands and individual swallowing muscles. Proton plans were made using Multifield Optimization (MFO, using three, five, and seven fields) and Single-field Optimization (SFO, using three fields). OAR sparing was evaluated using mean dose to composite salivary glands (CompSal) and composite swallowing muscles (CompSwal). Plan robustness was determined for setup and range uncertainties (±3 mm for setup, ±3% HU) evaluating V95% and V107% for clinical target volumes.
  
  
  RESULTS
  Averaged over all patients CompSal/CompSwal mean doses were lower for the three-field MFO plans (14.6/16.4 Gy) compared to the three-field SFO plans (20.0/23.7 Gy) and VMAT plans (23.0/25.3 Gy). Using more than three fields resulted in differences in OAR sparing of less than 1.5 Gy between plans. SFO plans were significantly more robust than MFO plans. VMAT plans were the most robust.
  
  
  CONCLUSIONS
  MFO plans had improved OAR sparing but were less robust than SFO and VMAT plans, while SFO plans were more robust than MFO plans but resulted in less OAR sparing. Robustness of the MFO plans did not increase with more fields.
authors.affiliation: Department of Radiotherapy, VU University Medical Center, De Boelelaan 1118, Amsterdam 1081 HV, The Netherlands.
authors.forename: Danique L J
authors.initials: DL
authors.lastname: Barten
authors.affiliation: Department of Radiotherapy, VU University Medical Center, De Boelelaan 1118, Amsterdam 1081 HV, The Netherlands.
authors.forename: Jim P
authors.initials: JP
authors.lastname: Tol
authors.affiliation: Department of Radiotherapy, VU University Medical Center, De Boelelaan 1118, Amsterdam 1081 HV, The Netherlands.
authors.forename: Max
authors.initials: M
authors.lastname: Dahele
authors.affiliation: Department of Radiotherapy, VU University Medical Center, De Boelelaan 1118, Amsterdam 1081 HV, The Netherlands.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Slotman
authors.affiliation: Department of Radiotherapy, VU University Medical Center, De Boelelaan 1118, Amsterdam 1081 HV, The Netherlands.
authors.forename: Wilko F A R
authors.initials: WF
authors.lastname: Verbakel
mesh_terms: D003198:Computer Simulation; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D009334:Neck Muscles / Q000528:radiation effects; D058958:Organs at Risk / Q000528:radiation effects*; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy / Q000379:methods*; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012469:Salivary Glands / Q000528:radiation effects; D011522:Protons
chemical_list: D011522:Protons