title: Intensity modulation in radiotherapy: photons versus protons in the paranasal sinus.
abstract: OBJECTIVE
  The purpose of this study is to investigate whether successive tightening of normal tissue constraints on an intensity modulated X-ray therapy plan might be able to improve it to the point of clinical comparability with the corresponding intensity modulated proton therapy plan.
  
  
  METHODS
  Photon and proton intensity modulated plans were calculated for a paranasal sinus case using nominal dose constraints. Additional photon plans were then calculated in an effort to match the dose-volume histograms of the critical structures to those of the proton plan.
  
  
  RESULTS
  On reducing the low dose contribution to both orbits in the photon plan by tightening the constraints on these structures, an increased dose heterogeneity across the target resulted. When all critical structures were more strictly constrained, target dose homogeneity and conformity was further compromised. An increased integral dose to the non-critical normal tissues was observed for the photon plans as dose was progressively removed from the critical structures.
  
  
  CONCLUSIONS
  Both modalities were found to provide comparable target volume conformation and sparing of critical structures, when the nominal dose constraints were applied. However, the use of intensity modulated protons provided the only method by which critical structures could be spared at all dose levels, whilst simultaneously providing acceptable dose homogeneity within the target volume.
authors.affiliation: Division of Radiation Oncology, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Anthony John
authors.initials: AJ
authors.lastname: Lomax
authors.forename: Michael
authors.initials: M
authors.lastname: Goitein
authors.forename: Judy
authors.initials: J
authors.lastname: Adams
mesh_terms: D000465:Algorithms; D004307:Dose-Response Relationship, Radiation; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D010256:Paranasal Sinuses / Q000528:radiation effects*; D017785:Photons; D011522:Protons; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D012680:Sensitivity and Specificity
chemical_list: D011522:Protons