title: An Analysis of Plan Robustness for Esophageal Tumors: Comparing Volumetric Modulated Arc Therapy Plans and Spot Scanning Proton Planning.
abstract: OBJECTIVE
  Planning studies to compare x-ray and proton techniques and to select the most suitable technique for each patient have been hampered by the nonequivalence of several aspects of treatment planning and delivery. A fair comparison should compare similarly advanced delivery techniques from current clinical practice and also assess the robustness of each technique. The present study therefore compared volumetric modulated arc therapy (VMAT) and single-field optimization (SFO) spot scanning proton therapy plans created using a simultaneous integrated boost (SIB) for dose escalation in midesophageal cancer and analyzed the effect of setup and range uncertainties on these plans.
  
  
  METHODS
  For 21 patients, SIB plans with a physical dose prescription of 2 Gy or 2.5 Gy/fraction in 25 fractions to planning target volume (PTV)50Gy or PTV62.5Gy (primary tumor with 0.5 cm margins) were created and evaluated for robustness to random setup errors and proton range errors. Dose-volume metrics were compared for the optimal and uncertainty plans, with P<.05 (Wilcoxon) considered significant.
  
  
  RESULTS
  SFO reduced the mean lung dose by 51.4% (range 35.1%-76.1%) and the mean heart dose by 40.9% (range 15.0%-57.4%) compared with VMAT. Proton plan robustness to a 3.5% range error was acceptable. For all patients, the clinical target volume D98 was 95.0% to 100.4% of the prescribed dose and gross tumor volume (GTV) D98 was 98.8% to 101%. Setup error robustness was patient anatomy dependent, and the potential minimum dose per fraction was always lower with SFO than with VMAT. The clinical target volume D98 was lower by 0.6% to 7.8% of the prescribed dose, and the GTV D98 was lower by 0.3% to 2.2% of the prescribed GTV dose.
  
  
  CONCLUSIONS
  The SFO plans achieved significant sparing of normal tissue compared with the VMAT plans for midesophageal cancer. The target dose coverage in the SIB proton plans was less robust to random setup errors and might be unacceptable for certain patients. Robust optimization to ensure adequate target coverage of SIB proton plans might be beneficial.
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, Oxford, United Kingdom. Electronic address: samantha.warren@oncology.ox.ac.uk.
authors.forename: Samantha
authors.initials: S
authors.lastname: Warren
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, Oxford, United Kingdom.
authors.forename: Mike
authors.initials: M
authors.lastname: Partridge
authors.affiliation: Centre for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Bolsi
authors.affiliation: Centre for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Lomax
authors.affiliation: Wales Cancer Trials Unit, School of Medicine, Heath Park, Cardiff, United Kingdom.
authors.forename: Chris
authors.initials: C
authors.lastname: Hurt
authors.affiliation: Velindre Cancer Centre, Velindre Hospital, Cardiff, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Crosby
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, Oxford, United Kingdom.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Hawkins
mesh_terms: D000465:Algorithms; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D001842:Bone and Bones / Q000000981:diagnostic imaging; D004938:Esophageal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006321:Heart / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000528:radiation effects; D059351:Organ Sparing Treatments / Q000379:methods*; D058958:Organs at Risk / Q000528:radiation effects; D061766:Proton Therapy / Q000379:methods*; D011832:Radiation Injuries / Q000517:prevention & control; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D035501:Uncertainty